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llvm-project/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

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//===- InstCombineCompares.cpp --------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitICmp and visitFCmp functions.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
// How many times is a select replaced by one of its operands?
STATISTIC(NumSel, "Number of select opts");
static ConstantInt *extractElement(Constant *V, Constant *Idx) {
return cast<ConstantInt>(ConstantExpr::getExtractElement(V, Idx));
}
static bool hasAddOverflow(ConstantInt *Result,
ConstantInt *In1, ConstantInt *In2,
bool IsSigned) {
if (!IsSigned)
return Result->getValue().ult(In1->getValue());
if (In2->isNegative())
return Result->getValue().sgt(In1->getValue());
return Result->getValue().slt(In1->getValue());
}
/// Compute Result = In1+In2, returning true if the result overflowed for this
/// type.
static bool addWithOverflow(Constant *&Result, Constant *In1,
Constant *In2, bool IsSigned = false) {
Result = ConstantExpr::getAdd(In1, In2);
if (VectorType *VTy = dyn_cast<VectorType>(In1->getType())) {
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i);
if (hasAddOverflow(extractElement(Result, Idx),
extractElement(In1, Idx),
extractElement(In2, Idx),
IsSigned))
return true;
}
return false;
}
return hasAddOverflow(cast<ConstantInt>(Result),
cast<ConstantInt>(In1), cast<ConstantInt>(In2),
IsSigned);
}
static bool hasSubOverflow(ConstantInt *Result,
ConstantInt *In1, ConstantInt *In2,
bool IsSigned) {
if (!IsSigned)
return Result->getValue().ugt(In1->getValue());
if (In2->isNegative())
return Result->getValue().slt(In1->getValue());
return Result->getValue().sgt(In1->getValue());
}
/// Compute Result = In1-In2, returning true if the result overflowed for this
/// type.
static bool subWithOverflow(Constant *&Result, Constant *In1,
Constant *In2, bool IsSigned = false) {
Result = ConstantExpr::getSub(In1, In2);
if (VectorType *VTy = dyn_cast<VectorType>(In1->getType())) {
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i);
if (hasSubOverflow(extractElement(Result, Idx),
extractElement(In1, Idx),
extractElement(In2, Idx),
IsSigned))
return true;
}
return false;
}
return hasSubOverflow(cast<ConstantInt>(Result),
cast<ConstantInt>(In1), cast<ConstantInt>(In2),
IsSigned);
}
/// Given an icmp instruction, return true if any use of this comparison is a
/// branch on sign bit comparison.
static bool hasBranchUse(ICmpInst &I) {
for (auto *U : I.users())
if (isa<BranchInst>(U))
return true;
return false;
}
/// Given an exploded icmp instruction, return true if the comparison only
/// checks the sign bit. If it only checks the sign bit, set TrueIfSigned if the
/// result of the comparison is true when the input value is signed.
static bool isSignBitCheck(ICmpInst::Predicate Pred, const APInt &RHS,
bool &TrueIfSigned) {
switch (Pred) {
case ICmpInst::ICMP_SLT: // True if LHS s< 0
TrueIfSigned = true;
return RHS.isNullValue();
case ICmpInst::ICMP_SLE: // True if LHS s<= RHS and RHS == -1
TrueIfSigned = true;
return RHS.isAllOnesValue();
case ICmpInst::ICMP_SGT: // True if LHS s> -1
TrueIfSigned = false;
return RHS.isAllOnesValue();
case ICmpInst::ICMP_UGT:
// True if LHS u> RHS and RHS == high-bit-mask - 1
TrueIfSigned = true;
return RHS.isMaxSignedValue();
case ICmpInst::ICMP_UGE:
// True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc)
TrueIfSigned = true;
return RHS.isSignMask();
default:
return false;
}
}
/// Returns true if the exploded icmp can be expressed as a signed comparison
/// to zero and updates the predicate accordingly.
/// The signedness of the comparison is preserved.
/// TODO: Refactor with decomposeBitTestICmp()?
static bool isSignTest(ICmpInst::Predicate &Pred, const APInt &C) {
if (!ICmpInst::isSigned(Pred))
return false;
if (C.isNullValue())
return ICmpInst::isRelational(Pred);
if (C.isOneValue()) {
if (Pred == ICmpInst::ICMP_SLT) {
Pred = ICmpInst::ICMP_SLE;
return true;
}
} else if (C.isAllOnesValue()) {
if (Pred == ICmpInst::ICMP_SGT) {
Pred = ICmpInst::ICMP_SGE;
return true;
}
}
return false;
}
/// Given a signed integer type and a set of known zero and one bits, compute
/// the maximum and minimum values that could have the specified known zero and
/// known one bits, returning them in Min/Max.
/// TODO: Move to method on KnownBits struct?
static void computeSignedMinMaxValuesFromKnownBits(const KnownBits &Known,
APInt &Min, APInt &Max) {
assert(Known.getBitWidth() == Min.getBitWidth() &&
Known.getBitWidth() == Max.getBitWidth() &&
"KnownZero, KnownOne and Min, Max must have equal bitwidth.");
APInt UnknownBits = ~(Known.Zero|Known.One);
// The minimum value is when all unknown bits are zeros, EXCEPT for the sign
// bit if it is unknown.
Min = Known.One;
Max = Known.One|UnknownBits;
if (UnknownBits.isNegative()) { // Sign bit is unknown
Min.setSignBit();
Max.clearSignBit();
}
}
/// Given an unsigned integer type and a set of known zero and one bits, compute
/// the maximum and minimum values that could have the specified known zero and
/// known one bits, returning them in Min/Max.
/// TODO: Move to method on KnownBits struct?
static void computeUnsignedMinMaxValuesFromKnownBits(const KnownBits &Known,
APInt &Min, APInt &Max) {
assert(Known.getBitWidth() == Min.getBitWidth() &&
Known.getBitWidth() == Max.getBitWidth() &&
"Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth.");
APInt UnknownBits = ~(Known.Zero|Known.One);
// The minimum value is when the unknown bits are all zeros.
Min = Known.One;
// The maximum value is when the unknown bits are all ones.
Max = Known.One|UnknownBits;
}
/// This is called when we see this pattern:
/// cmp pred (load (gep GV, ...)), cmpcst
/// where GV is a global variable with a constant initializer. Try to simplify
/// this into some simple computation that does not need the load. For example
/// we can optimize "icmp eq (load (gep "foo", 0, i)), 0" into "icmp eq i, 3".
///
/// If AndCst is non-null, then the loaded value is masked with that constant
/// before doing the comparison. This handles cases like "A[i]&4 == 0".
Instruction *InstCombiner::foldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP,
GlobalVariable *GV,
CmpInst &ICI,
ConstantInt *AndCst) {
Constant *Init = GV->getInitializer();
if (!isa<ConstantArray>(Init) && !isa<ConstantDataArray>(Init))
return nullptr;
uint64_t ArrayElementCount = Init->getType()->getArrayNumElements();
// Don't blow up on huge arrays.
if (ArrayElementCount > MaxArraySizeForCombine)
return nullptr;
// There are many forms of this optimization we can handle, for now, just do
// the simple index into a single-dimensional array.
//
// Require: GEP GV, 0, i {{, constant indices}}
if (GEP->getNumOperands() < 3 ||
!isa<ConstantInt>(GEP->getOperand(1)) ||
!cast<ConstantInt>(GEP->getOperand(1))->isZero() ||
isa<Constant>(GEP->getOperand(2)))
return nullptr;
// Check that indices after the variable are constants and in-range for the
// type they index. Collect the indices. This is typically for arrays of
// structs.
SmallVector<unsigned, 4> LaterIndices;
Type *EltTy = Init->getType()->getArrayElementType();
for (unsigned i = 3, e = GEP->getNumOperands(); i != e; ++i) {
ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!Idx) return nullptr; // Variable index.
uint64_t IdxVal = Idx->getZExtValue();
if ((unsigned)IdxVal != IdxVal) return nullptr; // Too large array index.
if (StructType *STy = dyn_cast<StructType>(EltTy))
EltTy = STy->getElementType(IdxVal);
else if (ArrayType *ATy = dyn_cast<ArrayType>(EltTy)) {
if (IdxVal >= ATy->getNumElements()) return nullptr;
EltTy = ATy->getElementType();
} else {
return nullptr; // Unknown type.
}
LaterIndices.push_back(IdxVal);
}
enum { Overdefined = -3, Undefined = -2 };
// Variables for our state machines.
// FirstTrueElement/SecondTrueElement - Used to emit a comparison of the form
// "i == 47 | i == 87", where 47 is the first index the condition is true for,
// and 87 is the second (and last) index. FirstTrueElement is -2 when
// undefined, otherwise set to the first true element. SecondTrueElement is
// -2 when undefined, -3 when overdefined and >= 0 when that index is true.
int FirstTrueElement = Undefined, SecondTrueElement = Undefined;
// FirstFalseElement/SecondFalseElement - Used to emit a comparison of the
// form "i != 47 & i != 87". Same state transitions as for true elements.
int FirstFalseElement = Undefined, SecondFalseElement = Undefined;
/// TrueRangeEnd/FalseRangeEnd - In conjunction with First*Element, these
/// define a state machine that triggers for ranges of values that the index
/// is true or false for. This triggers on things like "abbbbc"[i] == 'b'.
/// This is -2 when undefined, -3 when overdefined, and otherwise the last
/// index in the range (inclusive). We use -2 for undefined here because we
/// use relative comparisons and don't want 0-1 to match -1.
int TrueRangeEnd = Undefined, FalseRangeEnd = Undefined;
// MagicBitvector - This is a magic bitvector where we set a bit if the
// comparison is true for element 'i'. If there are 64 elements or less in
// the array, this will fully represent all the comparison results.
uint64_t MagicBitvector = 0;
// Scan the array and see if one of our patterns matches.
Constant *CompareRHS = cast<Constant>(ICI.getOperand(1));
for (unsigned i = 0, e = ArrayElementCount; i != e; ++i) {
Constant *Elt = Init->getAggregateElement(i);
if (!Elt) return nullptr;
// If this is indexing an array of structures, get the structure element.
if (!LaterIndices.empty())
Elt = ConstantExpr::getExtractValue(Elt, LaterIndices);
// If the element is masked, handle it.
if (AndCst) Elt = ConstantExpr::getAnd(Elt, AndCst);
// Find out if the comparison would be true or false for the i'th element.
Constant *C = ConstantFoldCompareInstOperands(ICI.getPredicate(), Elt,
CompareRHS, DL, &TLI);
// If the result is undef for this element, ignore it.
if (isa<UndefValue>(C)) {
// Extend range state machines to cover this element in case there is an
// undef in the middle of the range.
if (TrueRangeEnd == (int)i-1)
TrueRangeEnd = i;
if (FalseRangeEnd == (int)i-1)
FalseRangeEnd = i;
continue;
}
// If we can't compute the result for any of the elements, we have to give
// up evaluating the entire conditional.
if (!isa<ConstantInt>(C)) return nullptr;
// Otherwise, we know if the comparison is true or false for this element,
// update our state machines.
bool IsTrueForElt = !cast<ConstantInt>(C)->isZero();
// State machine for single/double/range index comparison.
if (IsTrueForElt) {
// Update the TrueElement state machine.
if (FirstTrueElement == Undefined)
FirstTrueElement = TrueRangeEnd = i; // First true element.
else {
// Update double-compare state machine.
if (SecondTrueElement == Undefined)
SecondTrueElement = i;
else
SecondTrueElement = Overdefined;
// Update range state machine.
if (TrueRangeEnd == (int)i-1)
TrueRangeEnd = i;
else
TrueRangeEnd = Overdefined;
}
} else {
// Update the FalseElement state machine.
if (FirstFalseElement == Undefined)
FirstFalseElement = FalseRangeEnd = i; // First false element.
else {
// Update double-compare state machine.
if (SecondFalseElement == Undefined)
SecondFalseElement = i;
else
SecondFalseElement = Overdefined;
// Update range state machine.
if (FalseRangeEnd == (int)i-1)
FalseRangeEnd = i;
else
FalseRangeEnd = Overdefined;
}
}
// If this element is in range, update our magic bitvector.
if (i < 64 && IsTrueForElt)
MagicBitvector |= 1ULL << i;
// If all of our states become overdefined, bail out early. Since the
// predicate is expensive, only check it every 8 elements. This is only
// really useful for really huge arrays.
if ((i & 8) == 0 && i >= 64 && SecondTrueElement == Overdefined &&
SecondFalseElement == Overdefined && TrueRangeEnd == Overdefined &&
FalseRangeEnd == Overdefined)
return nullptr;
}
// Now that we've scanned the entire array, emit our new comparison(s). We
// order the state machines in complexity of the generated code.
Value *Idx = GEP->getOperand(2);
// If the index is larger than the pointer size of the target, truncate the
// index down like the GEP would do implicitly. We don't have to do this for
// an inbounds GEP because the index can't be out of range.
if (!GEP->isInBounds()) {
Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
unsigned PtrSize = IntPtrTy->getIntegerBitWidth();
if (Idx->getType()->getPrimitiveSizeInBits() > PtrSize)
Idx = Builder.CreateTrunc(Idx, IntPtrTy);
}
// If the comparison is only true for one or two elements, emit direct
// comparisons.
if (SecondTrueElement != Overdefined) {
// None true -> false.
if (FirstTrueElement == Undefined)
return replaceInstUsesWith(ICI, Builder.getFalse());
Value *FirstTrueIdx = ConstantInt::get(Idx->getType(), FirstTrueElement);
// True for one element -> 'i == 47'.
if (SecondTrueElement == Undefined)
return new ICmpInst(ICmpInst::ICMP_EQ, Idx, FirstTrueIdx);
// True for two elements -> 'i == 47 | i == 72'.
Value *C1 = Builder.CreateICmpEQ(Idx, FirstTrueIdx);
Value *SecondTrueIdx = ConstantInt::get(Idx->getType(), SecondTrueElement);
Value *C2 = Builder.CreateICmpEQ(Idx, SecondTrueIdx);
return BinaryOperator::CreateOr(C1, C2);
}
// If the comparison is only false for one or two elements, emit direct
// comparisons.
if (SecondFalseElement != Overdefined) {
// None false -> true.
if (FirstFalseElement == Undefined)
return replaceInstUsesWith(ICI, Builder.getTrue());
Value *FirstFalseIdx = ConstantInt::get(Idx->getType(), FirstFalseElement);
// False for one element -> 'i != 47'.
if (SecondFalseElement == Undefined)
return new ICmpInst(ICmpInst::ICMP_NE, Idx, FirstFalseIdx);
// False for two elements -> 'i != 47 & i != 72'.
Value *C1 = Builder.CreateICmpNE(Idx, FirstFalseIdx);
Value *SecondFalseIdx = ConstantInt::get(Idx->getType(),SecondFalseElement);
Value *C2 = Builder.CreateICmpNE(Idx, SecondFalseIdx);
return BinaryOperator::CreateAnd(C1, C2);
}
// If the comparison can be replaced with a range comparison for the elements
// where it is true, emit the range check.
if (TrueRangeEnd != Overdefined) {
assert(TrueRangeEnd != FirstTrueElement && "Should emit single compare");
// Generate (i-FirstTrue) <u (TrueRangeEnd-FirstTrue+1).
if (FirstTrueElement) {
Value *Offs = ConstantInt::get(Idx->getType(), -FirstTrueElement);
Idx = Builder.CreateAdd(Idx, Offs);
}
Value *End = ConstantInt::get(Idx->getType(),
TrueRangeEnd-FirstTrueElement+1);
return new ICmpInst(ICmpInst::ICMP_ULT, Idx, End);
}
// False range check.
if (FalseRangeEnd != Overdefined) {
assert(FalseRangeEnd != FirstFalseElement && "Should emit single compare");
// Generate (i-FirstFalse) >u (FalseRangeEnd-FirstFalse).
if (FirstFalseElement) {
Value *Offs = ConstantInt::get(Idx->getType(), -FirstFalseElement);
Idx = Builder.CreateAdd(Idx, Offs);
}
Value *End = ConstantInt::get(Idx->getType(),
FalseRangeEnd-FirstFalseElement);
return new ICmpInst(ICmpInst::ICMP_UGT, Idx, End);
}
// If a magic bitvector captures the entire comparison state
// of this load, replace it with computation that does:
// ((magic_cst >> i) & 1) != 0
{
Type *Ty = nullptr;
// Look for an appropriate type:
// - The type of Idx if the magic fits
// - The smallest fitting legal type if we have a DataLayout
// - Default to i32
if (ArrayElementCount <= Idx->getType()->getIntegerBitWidth())
Ty = Idx->getType();
else
Ty = DL.getSmallestLegalIntType(Init->getContext(), ArrayElementCount);
if (Ty) {
Value *V = Builder.CreateIntCast(Idx, Ty, false);
V = Builder.CreateLShr(ConstantInt::get(Ty, MagicBitvector), V);
V = Builder.CreateAnd(ConstantInt::get(Ty, 1), V);
return new ICmpInst(ICmpInst::ICMP_NE, V, ConstantInt::get(Ty, 0));
}
}
return nullptr;
}
/// Return a value that can be used to compare the *offset* implied by a GEP to
/// zero. For example, if we have &A[i], we want to return 'i' for
/// "icmp ne i, 0". Note that, in general, indices can be complex, and scales
/// are involved. The above expression would also be legal to codegen as
/// "icmp ne (i*4), 0" (assuming A is a pointer to i32).
/// This latter form is less amenable to optimization though, and we are allowed
/// to generate the first by knowing that pointer arithmetic doesn't overflow.
///
/// If we can't emit an optimized form for this expression, this returns null.
///
static Value *evaluateGEPOffsetExpression(User *GEP, InstCombiner &IC,
const DataLayout &DL) {
gep_type_iterator GTI = gep_type_begin(GEP);
// Check to see if this gep only has a single variable index. If so, and if
// any constant indices are a multiple of its scale, then we can compute this
// in terms of the scale of the variable index. For example, if the GEP
// implies an offset of "12 + i*4", then we can codegen this as "3 + i",
// because the expression will cross zero at the same point.
unsigned i, e = GEP->getNumOperands();
int64_t Offset = 0;
for (i = 1; i != e; ++i, ++GTI) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i))) {
// Compute the aggregate offset of constant indices.
if (CI->isZero()) continue;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = GTI.getStructTypeOrNull()) {
Offset += DL.getStructLayout(STy)->getElementOffset(CI->getZExtValue());
} else {
uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
Offset += Size*CI->getSExtValue();
}
} else {
// Found our variable index.
break;
}
}
// If there are no variable indices, we must have a constant offset, just
// evaluate it the general way.
if (i == e) return nullptr;
Value *VariableIdx = GEP->getOperand(i);
// Determine the scale factor of the variable element. For example, this is
// 4 if the variable index is into an array of i32.
uint64_t VariableScale = DL.getTypeAllocSize(GTI.getIndexedType());
// Verify that there are no other variable indices. If so, emit the hard way.
for (++i, ++GTI; i != e; ++i, ++GTI) {
ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!CI) return nullptr;
// Compute the aggregate offset of constant indices.
if (CI->isZero()) continue;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = GTI.getStructTypeOrNull()) {
Offset += DL.getStructLayout(STy)->getElementOffset(CI->getZExtValue());
} else {
uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
Offset += Size*CI->getSExtValue();
}
}
// Okay, we know we have a single variable index, which must be a
// pointer/array/vector index. If there is no offset, life is simple, return
// the index.
Type *IntPtrTy = DL.getIntPtrType(GEP->getOperand(0)->getType());
unsigned IntPtrWidth = IntPtrTy->getIntegerBitWidth();
if (Offset == 0) {
// Cast to intptrty in case a truncation occurs. If an extension is needed,
// we don't need to bother extending: the extension won't affect where the
// computation crosses zero.
if (VariableIdx->getType()->getPrimitiveSizeInBits() > IntPtrWidth) {
VariableIdx = IC.Builder.CreateTrunc(VariableIdx, IntPtrTy);
}
return VariableIdx;
}
// Otherwise, there is an index. The computation we will do will be modulo
// the pointer size, so get it.
uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth);
Offset &= PtrSizeMask;
VariableScale &= PtrSizeMask;
// To do this transformation, any constant index must be a multiple of the
// variable scale factor. For example, we can evaluate "12 + 4*i" as "3 + i",
// but we can't evaluate "10 + 3*i" in terms of i. Check that the offset is a
// multiple of the variable scale.
int64_t NewOffs = Offset / (int64_t)VariableScale;
if (Offset != NewOffs*(int64_t)VariableScale)
return nullptr;
// Okay, we can do this evaluation. Start by converting the index to intptr.
if (VariableIdx->getType() != IntPtrTy)
VariableIdx = IC.Builder.CreateIntCast(VariableIdx, IntPtrTy,
true /*Signed*/);
Constant *OffsetVal = ConstantInt::get(IntPtrTy, NewOffs);
return IC.Builder.CreateAdd(VariableIdx, OffsetVal, "offset");
}
/// Returns true if we can rewrite Start as a GEP with pointer Base
/// and some integer offset. The nodes that need to be re-written
/// for this transformation will be added to Explored.
static bool canRewriteGEPAsOffset(Value *Start, Value *Base,
const DataLayout &DL,
SetVector<Value *> &Explored) {
SmallVector<Value *, 16> WorkList(1, Start);
Explored.insert(Base);
// The following traversal gives us an order which can be used
// when doing the final transformation. Since in the final
// transformation we create the PHI replacement instructions first,
// we don't have to get them in any particular order.
//
// However, for other instructions we will have to traverse the
// operands of an instruction first, which means that we have to
// do a post-order traversal.
while (!WorkList.empty()) {
SetVector<PHINode *> PHIs;
while (!WorkList.empty()) {
if (Explored.size() >= 100)
return false;
Value *V = WorkList.back();
if (Explored.count(V) != 0) {
WorkList.pop_back();
continue;
}
if (!isa<IntToPtrInst>(V) && !isa<PtrToIntInst>(V) &&
!isa<GetElementPtrInst>(V) && !isa<PHINode>(V))
// We've found some value that we can't explore which is different from
// the base. Therefore we can't do this transformation.
return false;
if (isa<IntToPtrInst>(V) || isa<PtrToIntInst>(V)) {
auto *CI = dyn_cast<CastInst>(V);
if (!CI->isNoopCast(DL))
return false;
if (Explored.count(CI->getOperand(0)) == 0)
WorkList.push_back(CI->getOperand(0));
}
if (auto *GEP = dyn_cast<GEPOperator>(V)) {
// We're limiting the GEP to having one index. This will preserve
// the original pointer type. We could handle more cases in the
// future.
if (GEP->getNumIndices() != 1 || !GEP->isInBounds() ||
GEP->getType() != Start->getType())
return false;
if (Explored.count(GEP->getOperand(0)) == 0)
WorkList.push_back(GEP->getOperand(0));
}
if (WorkList.back() == V) {
WorkList.pop_back();
// We've finished visiting this node, mark it as such.
Explored.insert(V);
}
if (auto *PN = dyn_cast<PHINode>(V)) {
// We cannot transform PHIs on unsplittable basic blocks.
if (isa<CatchSwitchInst>(PN->getParent()->getTerminator()))
return false;
Explored.insert(PN);
PHIs.insert(PN);
}
}
// Explore the PHI nodes further.
for (auto *PN : PHIs)
for (Value *Op : PN->incoming_values())
if (Explored.count(Op) == 0)
WorkList.push_back(Op);
}
// Make sure that we can do this. Since we can't insert GEPs in a basic
// block before a PHI node, we can't easily do this transformation if
// we have PHI node users of transformed instructions.
for (Value *Val : Explored) {
for (Value *Use : Val->uses()) {
auto *PHI = dyn_cast<PHINode>(Use);
auto *Inst = dyn_cast<Instruction>(Val);
if (Inst == Base || Inst == PHI || !Inst || !PHI ||
Explored.count(PHI) == 0)
continue;
if (PHI->getParent() == Inst->getParent())
return false;
}
}
return true;
}
// Sets the appropriate insert point on Builder where we can add
// a replacement Instruction for V (if that is possible).
static void setInsertionPoint(IRBuilder<> &Builder, Value *V,
bool Before = true) {
if (auto *PHI = dyn_cast<PHINode>(V)) {
Builder.SetInsertPoint(&*PHI->getParent()->getFirstInsertionPt());
return;
}
if (auto *I = dyn_cast<Instruction>(V)) {
if (!Before)
I = &*std::next(I->getIterator());
Builder.SetInsertPoint(I);
return;
}
if (auto *A = dyn_cast<Argument>(V)) {
// Set the insertion point in the entry block.
BasicBlock &Entry = A->getParent()->getEntryBlock();
Builder.SetInsertPoint(&*Entry.getFirstInsertionPt());
return;
}
// Otherwise, this is a constant and we don't need to set a new
// insertion point.
assert(isa<Constant>(V) && "Setting insertion point for unknown value!");
}
/// Returns a re-written value of Start as an indexed GEP using Base as a
/// pointer.
static Value *rewriteGEPAsOffset(Value *Start, Value *Base,
const DataLayout &DL,
SetVector<Value *> &Explored) {
// Perform all the substitutions. This is a bit tricky because we can
// have cycles in our use-def chains.
// 1. Create the PHI nodes without any incoming values.
// 2. Create all the other values.
// 3. Add the edges for the PHI nodes.
// 4. Emit GEPs to get the original pointers.
// 5. Remove the original instructions.
Type *IndexType = IntegerType::get(
Base->getContext(), DL.getPointerTypeSizeInBits(Start->getType()));
DenseMap<Value *, Value *> NewInsts;
NewInsts[Base] = ConstantInt::getNullValue(IndexType);
// Create the new PHI nodes, without adding any incoming values.
for (Value *Val : Explored) {
if (Val == Base)
continue;
// Create empty phi nodes. This avoids cyclic dependencies when creating
// the remaining instructions.
if (auto *PHI = dyn_cast<PHINode>(Val))
NewInsts[PHI] = PHINode::Create(IndexType, PHI->getNumIncomingValues(),
PHI->getName() + ".idx", PHI);
}
IRBuilder<> Builder(Base->getContext());
// Create all the other instructions.
for (Value *Val : Explored) {
if (NewInsts.find(Val) != NewInsts.end())
continue;
if (auto *CI = dyn_cast<CastInst>(Val)) {
NewInsts[CI] = NewInsts[CI->getOperand(0)];
continue;
}
if (auto *GEP = dyn_cast<GEPOperator>(Val)) {
Value *Index = NewInsts[GEP->getOperand(1)] ? NewInsts[GEP->getOperand(1)]
: GEP->getOperand(1);
setInsertionPoint(Builder, GEP);
// Indices might need to be sign extended. GEPs will magically do
// this, but we need to do it ourselves here.
if (Index->getType()->getScalarSizeInBits() !=
NewInsts[GEP->getOperand(0)]->getType()->getScalarSizeInBits()) {
Index = Builder.CreateSExtOrTrunc(
Index, NewInsts[GEP->getOperand(0)]->getType(),
GEP->getOperand(0)->getName() + ".sext");
}
auto *Op = NewInsts[GEP->getOperand(0)];
if (isa<ConstantInt>(Op) && dyn_cast<ConstantInt>(Op)->isZero())
NewInsts[GEP] = Index;
else
NewInsts[GEP] = Builder.CreateNSWAdd(
Op, Index, GEP->getOperand(0)->getName() + ".add");
continue;
}
if (isa<PHINode>(Val))
continue;
llvm_unreachable("Unexpected instruction type");
}
// Add the incoming values to the PHI nodes.
for (Value *Val : Explored) {
if (Val == Base)
continue;
// All the instructions have been created, we can now add edges to the
// phi nodes.
if (auto *PHI = dyn_cast<PHINode>(Val)) {
PHINode *NewPhi = static_cast<PHINode *>(NewInsts[PHI]);
for (unsigned I = 0, E = PHI->getNumIncomingValues(); I < E; ++I) {
Value *NewIncoming = PHI->getIncomingValue(I);
if (NewInsts.find(NewIncoming) != NewInsts.end())
NewIncoming = NewInsts[NewIncoming];
NewPhi->addIncoming(NewIncoming, PHI->getIncomingBlock(I));
}
}
}
for (Value *Val : Explored) {
if (Val == Base)
continue;
// Depending on the type, for external users we have to emit
// a GEP or a GEP + ptrtoint.
setInsertionPoint(Builder, Val, false);
// If required, create an inttoptr instruction for Base.
Value *NewBase = Base;
if (!Base->getType()->isPointerTy())
NewBase = Builder.CreateBitOrPointerCast(Base, Start->getType(),
Start->getName() + "to.ptr");
Value *GEP = Builder.CreateInBoundsGEP(
Start->getType()->getPointerElementType(), NewBase,
makeArrayRef(NewInsts[Val]), Val->getName() + ".ptr");
if (!Val->getType()->isPointerTy()) {
Value *Cast = Builder.CreatePointerCast(GEP, Val->getType(),
Val->getName() + ".conv");
GEP = Cast;
}
Val->replaceAllUsesWith(GEP);
}
return NewInsts[Start];
}
/// Looks through GEPs, IntToPtrInsts and PtrToIntInsts in order to express
/// the input Value as a constant indexed GEP. Returns a pair containing
/// the GEPs Pointer and Index.
static std::pair<Value *, Value *>
getAsConstantIndexedAddress(Value *V, const DataLayout &DL) {
Type *IndexType = IntegerType::get(V->getContext(),
DL.getPointerTypeSizeInBits(V->getType()));
Constant *Index = ConstantInt::getNullValue(IndexType);
while (true) {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
// We accept only inbouds GEPs here to exclude the possibility of
// overflow.
if (!GEP->isInBounds())
break;
if (GEP->hasAllConstantIndices() && GEP->getNumIndices() == 1 &&
GEP->getType() == V->getType()) {
V = GEP->getOperand(0);
Constant *GEPIndex = static_cast<Constant *>(GEP->getOperand(1));
Index = ConstantExpr::getAdd(
Index, ConstantExpr::getSExtOrBitCast(GEPIndex, IndexType));
continue;
}
break;
}
if (auto *CI = dyn_cast<IntToPtrInst>(V)) {
if (!CI->isNoopCast(DL))
break;
V = CI->getOperand(0);
continue;
}
if (auto *CI = dyn_cast<PtrToIntInst>(V)) {
if (!CI->isNoopCast(DL))
break;
V = CI->getOperand(0);
continue;
}
break;
}
return {V, Index};
}
/// Converts (CMP GEPLHS, RHS) if this change would make RHS a constant.
/// We can look through PHIs, GEPs and casts in order to determine a common base
/// between GEPLHS and RHS.
static Instruction *transformToIndexedCompare(GEPOperator *GEPLHS, Value *RHS,
ICmpInst::Predicate Cond,
const DataLayout &DL) {
if (!GEPLHS->hasAllConstantIndices())
return nullptr;
// Make sure the pointers have the same type.
if (GEPLHS->getType() != RHS->getType())
return nullptr;
Value *PtrBase, *Index;
std::tie(PtrBase, Index) = getAsConstantIndexedAddress(GEPLHS, DL);
// The set of nodes that will take part in this transformation.
SetVector<Value *> Nodes;
if (!canRewriteGEPAsOffset(RHS, PtrBase, DL, Nodes))
return nullptr;
// We know we can re-write this as
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)
// Since we've only looked through inbouds GEPs we know that we
// can't have overflow on either side. We can therefore re-write
// this as:
// OFFSET1 cmp OFFSET2
Value *NewRHS = rewriteGEPAsOffset(RHS, PtrBase, DL, Nodes);
// RewriteGEPAsOffset has replaced RHS and all of its uses with a re-written
// GEP having PtrBase as the pointer base, and has returned in NewRHS the
// offset. Since Index is the offset of LHS to the base pointer, we will now
// compare the offsets instead of comparing the pointers.
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Index, NewRHS);
}
/// Fold comparisons between a GEP instruction and something else. At this point
/// we know that the GEP is on the LHS of the comparison.
Instruction *InstCombiner::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
ICmpInst::Predicate Cond,
Instruction &I) {
// Don't transform signed compares of GEPs into index compares. Even if the
// GEP is inbounds, the final add of the base pointer can have signed overflow
// and would change the result of the icmp.
// e.g. "&foo[0] <s &foo[1]" can't be folded to "true" because "foo" could be
// the maximum signed value for the pointer type.
if (ICmpInst::isSigned(Cond))
return nullptr;
// Look through bitcasts and addrspacecasts. We do not however want to remove
// 0 GEPs.
if (!isa<GetElementPtrInst>(RHS))
RHS = RHS->stripPointerCasts();
Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase == RHS && GEPLHS->isInBounds()) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
// This transformation (ignoring the base and scales) is valid because we
// know pointers can't overflow since the gep is inbounds. See if we can
// output an optimized form.
Value *Offset = evaluateGEPOffsetExpression(GEPLHS, *this, DL);
// If not, synthesize the offset the hard way.
if (!Offset)
Offset = EmitGEPOffset(GEPLHS);
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,
Constant::getNullValue(Offset->getType()));
} else if (GEPOperator *GEPRHS = dyn_cast<GEPOperator>(RHS)) {
// If the base pointers are different, but the indices are the same, just
// compare the base pointer.
if (PtrBase != GEPRHS->getOperand(0)) {
bool IndicesTheSame = GEPLHS->getNumOperands()==GEPRHS->getNumOperands();
IndicesTheSame &= GEPLHS->getOperand(0)->getType() ==
GEPRHS->getOperand(0)->getType();
if (IndicesTheSame)
for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i)
if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) {
IndicesTheSame = false;
break;
}
// If all indices are the same, just compare the base pointers.
if (IndicesTheSame)
return new ICmpInst(Cond, GEPLHS->getOperand(0), GEPRHS->getOperand(0));
// If we're comparing GEPs with two base pointers that only differ in type
// and both GEPs have only constant indices or just one use, then fold
// the compare with the adjusted indices.
if (GEPLHS->isInBounds() && GEPRHS->isInBounds() &&
(GEPLHS->hasAllConstantIndices() || GEPLHS->hasOneUse()) &&
(GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
PtrBase->stripPointerCasts() ==
GEPRHS->getOperand(0)->stripPointerCasts()) {
Value *LOffset = EmitGEPOffset(GEPLHS);
Value *ROffset = EmitGEPOffset(GEPRHS);
// If we looked through an addrspacecast between different sized address
// spaces, the LHS and RHS pointers are different sized
// integers. Truncate to the smaller one.
Type *LHSIndexTy = LOffset->getType();
Type *RHSIndexTy = ROffset->getType();
if (LHSIndexTy != RHSIndexTy) {
if (LHSIndexTy->getPrimitiveSizeInBits() <
RHSIndexTy->getPrimitiveSizeInBits()) {
ROffset = Builder.CreateTrunc(ROffset, LHSIndexTy);
} else
LOffset = Builder.CreateTrunc(LOffset, RHSIndexTy);
}
Value *Cmp = Builder.CreateICmp(ICmpInst::getSignedPredicate(Cond),
LOffset, ROffset);
return replaceInstUsesWith(I, Cmp);
}
// Otherwise, the base pointers are different and the indices are
// different. Try convert this to an indexed compare by looking through
// PHIs/casts.
return transformToIndexedCompare(GEPLHS, RHS, Cond, DL);
}
// If one of the GEPs has all zero indices, recurse.
if (GEPLHS->hasAllZeroIndices())
return foldGEPICmp(GEPRHS, GEPLHS->getOperand(0),
ICmpInst::getSwappedPredicate(Cond), I);
// If the other GEP has all zero indices, recurse.
if (GEPRHS->hasAllZeroIndices())
return foldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I);
bool GEPsInBounds = GEPLHS->isInBounds() && GEPRHS->isInBounds();
if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) {
// If the GEPs only differ by one index, compare it.
unsigned NumDifferences = 0; // Keep track of # differences.
unsigned DiffOperand = 0; // The operand that differs.
for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i)
if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) {
if (GEPLHS->getOperand(i)->getType()->getPrimitiveSizeInBits() !=
GEPRHS->getOperand(i)->getType()->getPrimitiveSizeInBits()) {
// Irreconcilable differences.
NumDifferences = 2;
break;
} else {
if (NumDifferences++) break;
DiffOperand = i;
}
}
if (NumDifferences == 0) // SAME GEP?
return replaceInstUsesWith(I, // No comparison is needed here.
Builder.getInt1(ICmpInst::isTrueWhenEqual(Cond)));
else if (NumDifferences == 1 && GEPsInBounds) {
Value *LHSV = GEPLHS->getOperand(DiffOperand);
Value *RHSV = GEPRHS->getOperand(DiffOperand);
// Make sure we do a signed comparison here.
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), LHSV, RHSV);
}
}
// Only lower this if the icmp is the only user of the GEP or if we expect
// the result to fold to a constant!
if (GEPsInBounds && (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
(isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
// ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2) ---> (OFFSET1 cmp OFFSET2)
Value *L = EmitGEPOffset(GEPLHS);
Value *R = EmitGEPOffset(GEPRHS);
return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R);
}
}
// Try convert this to an indexed compare by looking through PHIs/casts as a
// last resort.
return transformToIndexedCompare(GEPLHS, RHS, Cond, DL);
}
Instruction *InstCombiner::foldAllocaCmp(ICmpInst &ICI,
const AllocaInst *Alloca,
const Value *Other) {
assert(ICI.isEquality() && "Cannot fold non-equality comparison.");
// It would be tempting to fold away comparisons between allocas and any
// pointer not based on that alloca (e.g. an argument). However, even
// though such pointers cannot alias, they can still compare equal.
//
// But LLVM doesn't specify where allocas get their memory, so if the alloca
// doesn't escape we can argue that it's impossible to guess its value, and we
// can therefore act as if any such guesses are wrong.
//
// The code below checks that the alloca doesn't escape, and that it's only
// used in a comparison once (the current instruction). The
// single-comparison-use condition ensures that we're trivially folding all
// comparisons against the alloca consistently, and avoids the risk of
// erroneously folding a comparison of the pointer with itself.
unsigned MaxIter = 32; // Break cycles and bound to constant-time.
SmallVector<const Use *, 32> Worklist;
for (const Use &U : Alloca->uses()) {
if (Worklist.size() >= MaxIter)
return nullptr;
Worklist.push_back(&U);
}
unsigned NumCmps = 0;
while (!Worklist.empty()) {
assert(Worklist.size() <= MaxIter);
const Use *U = Worklist.pop_back_val();
const Value *V = U->getUser();
--MaxIter;
if (isa<BitCastInst>(V) || isa<GetElementPtrInst>(V) || isa<PHINode>(V) ||
isa<SelectInst>(V)) {
// Track the uses.
} else if (isa<LoadInst>(V)) {
// Loading from the pointer doesn't escape it.
continue;
} else if (const auto *SI = dyn_cast<StoreInst>(V)) {
// Storing *to* the pointer is fine, but storing the pointer escapes it.
if (SI->getValueOperand() == U->get())
return nullptr;
continue;
} else if (isa<ICmpInst>(V)) {
if (NumCmps++)
return nullptr; // Found more than one cmp.
continue;
} else if (const auto *Intrin = dyn_cast<IntrinsicInst>(V)) {
switch (Intrin->getIntrinsicID()) {
// These intrinsics don't escape or compare the pointer. Memset is safe
// because we don't allow ptrtoint. Memcpy and memmove are safe because
// we don't allow stores, so src cannot point to V.
case Intrinsic::lifetime_start: case Intrinsic::lifetime_end:
case Intrinsic::memcpy: case Intrinsic::memmove: case Intrinsic::memset:
continue;
default:
return nullptr;
}
} else {
return nullptr;
}
for (const Use &U : V->uses()) {
if (Worklist.size() >= MaxIter)
return nullptr;
Worklist.push_back(&U);
}
}
Type *CmpTy = CmpInst::makeCmpResultType(Other->getType());
return replaceInstUsesWith(
ICI,
ConstantInt::get(CmpTy, !CmpInst::isTrueWhenEqual(ICI.getPredicate())));
}
/// Fold "icmp pred (X+CI), X".
Instruction *InstCombiner::foldICmpAddOpConst(Value *X, ConstantInt *CI,
ICmpInst::Predicate Pred) {
// From this point on, we know that (X+C <= X) --> (X+C < X) because C != 0,
// so the values can never be equal. Similarly for all other "or equals"
// operators.
// (X+1) <u X --> X >u (MAXUINT-1) --> X == 255
// (X+2) <u X --> X >u (MAXUINT-2) --> X > 253
// (X+MAXUINT) <u X --> X >u (MAXUINT-MAXUINT) --> X != 0
if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) {
Value *R =
ConstantExpr::getSub(ConstantInt::getAllOnesValue(CI->getType()), CI);
return new ICmpInst(ICmpInst::ICMP_UGT, X, R);
}
// (X+1) >u X --> X <u (0-1) --> X != 255
// (X+2) >u X --> X <u (0-2) --> X <u 254
// (X+MAXUINT) >u X --> X <u (0-MAXUINT) --> X <u 1 --> X == 0
if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE)
return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantExpr::getNeg(CI));
unsigned BitWidth = CI->getType()->getPrimitiveSizeInBits();
ConstantInt *SMax = ConstantInt::get(X->getContext(),
APInt::getSignedMaxValue(BitWidth));
// (X+ 1) <s X --> X >s (MAXSINT-1) --> X == 127
// (X+ 2) <s X --> X >s (MAXSINT-2) --> X >s 125
// (X+MAXSINT) <s X --> X >s (MAXSINT-MAXSINT) --> X >s 0
// (X+MINSINT) <s X --> X >s (MAXSINT-MINSINT) --> X >s -1
// (X+ -2) <s X --> X >s (MAXSINT- -2) --> X >s 126
// (X+ -1) <s X --> X >s (MAXSINT- -1) --> X != 127
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_SGT, X, ConstantExpr::getSub(SMax, CI));
// (X+ 1) >s X --> X <s (MAXSINT-(1-1)) --> X != 127
// (X+ 2) >s X --> X <s (MAXSINT-(2-1)) --> X <s 126
// (X+MAXSINT) >s X --> X <s (MAXSINT-(MAXSINT-1)) --> X <s 1
// (X+MINSINT) >s X --> X <s (MAXSINT-(MINSINT-1)) --> X <s -2
// (X+ -2) >s X --> X <s (MAXSINT-(-2-1)) --> X <s -126
// (X+ -1) >s X --> X <s (MAXSINT-(-1-1)) --> X == -128
assert(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE);
Constant *C = Builder.getInt(CI->getValue() - 1);
return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C));
}
/// Handle "(icmp eq/ne (ashr/lshr AP2, A), AP1)" ->
/// (icmp eq/ne A, Log2(AP2/AP1)) ->
/// (icmp eq/ne A, Log2(AP2) - Log2(AP1)).
Instruction *InstCombiner::foldICmpShrConstConst(ICmpInst &I, Value *A,
const APInt &AP1,
const APInt &AP2) {
assert(I.isEquality() && "Cannot fold icmp gt/lt");
auto getICmp = [&I](CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
if (I.getPredicate() == I.ICMP_NE)
Pred = CmpInst::getInversePredicate(Pred);
return new ICmpInst(Pred, LHS, RHS);
};
// Don't bother doing any work for cases which InstSimplify handles.
if (AP2.isNullValue())
return nullptr;
bool IsAShr = isa<AShrOperator>(I.getOperand(0));
if (IsAShr) {
if (AP2.isAllOnesValue())
return nullptr;
if (AP2.isNegative() != AP1.isNegative())
return nullptr;
if (AP2.sgt(AP1))
return nullptr;
}
if (!AP1)
// 'A' must be large enough to shift out the highest set bit.
return getICmp(I.ICMP_UGT, A,
ConstantInt::get(A->getType(), AP2.logBase2()));
if (AP1 == AP2)
return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
int Shift;
if (IsAShr && AP1.isNegative())
Shift = AP1.countLeadingOnes() - AP2.countLeadingOnes();
else
Shift = AP1.countLeadingZeros() - AP2.countLeadingZeros();
if (Shift > 0) {
if (IsAShr && AP1 == AP2.ashr(Shift)) {
// There are multiple solutions if we are comparing against -1 and the LHS
// of the ashr is not a power of two.
if (AP1.isAllOnesValue() && !AP2.isPowerOf2())
return getICmp(I.ICMP_UGE, A, ConstantInt::get(A->getType(), Shift));
return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
} else if (AP1 == AP2.lshr(Shift)) {
return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
}
}
// Shifting const2 will never be equal to const1.
// FIXME: This should always be handled by InstSimplify?
auto *TorF = ConstantInt::get(I.getType(), I.getPredicate() == I.ICMP_NE);
return replaceInstUsesWith(I, TorF);
}
/// Handle "(icmp eq/ne (shl AP2, A), AP1)" ->
/// (icmp eq/ne A, TrailingZeros(AP1) - TrailingZeros(AP2)).
Instruction *InstCombiner::foldICmpShlConstConst(ICmpInst &I, Value *A,
const APInt &AP1,
const APInt &AP2) {
assert(I.isEquality() && "Cannot fold icmp gt/lt");
auto getICmp = [&I](CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
if (I.getPredicate() == I.ICMP_NE)
Pred = CmpInst::getInversePredicate(Pred);
return new ICmpInst(Pred, LHS, RHS);
};
// Don't bother doing any work for cases which InstSimplify handles.
if (AP2.isNullValue())
return nullptr;
unsigned AP2TrailingZeros = AP2.countTrailingZeros();
if (!AP1 && AP2TrailingZeros != 0)
return getICmp(
I.ICMP_UGE, A,
ConstantInt::get(A->getType(), AP2.getBitWidth() - AP2TrailingZeros));
if (AP1 == AP2)
return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
// Get the distance between the lowest bits that are set.
int Shift = AP1.countTrailingZeros() - AP2TrailingZeros;
if (Shift > 0 && AP2.shl(Shift) == AP1)
return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
// Shifting const2 will never be equal to const1.
// FIXME: This should always be handled by InstSimplify?
auto *TorF = ConstantInt::get(I.getType(), I.getPredicate() == I.ICMP_NE);
return replaceInstUsesWith(I, TorF);
}
/// The caller has matched a pattern of the form:
/// I = icmp ugt (add (add A, B), CI2), CI1
/// If this is of the form:
/// sum = a + b
/// if (sum+128 >u 255)
/// Then replace it with llvm.sadd.with.overflow.i8.
///
static Instruction *processUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
ConstantInt *CI2, ConstantInt *CI1,
InstCombiner &IC) {
// The transformation we're trying to do here is to transform this into an
// llvm.sadd.with.overflow. To do this, we have to replace the original add
// with a narrower add, and discard the add-with-constant that is part of the
// range check (if we can't eliminate it, this isn't profitable).
// In order to eliminate the add-with-constant, the compare can be its only
// use.
Instruction *AddWithCst = cast<Instruction>(I.getOperand(0));
if (!AddWithCst->hasOneUse())
return nullptr;
// If CI2 is 2^7, 2^15, 2^31, then it might be an sadd.with.overflow.
if (!CI2->getValue().isPowerOf2())
return nullptr;
unsigned NewWidth = CI2->getValue().countTrailingZeros();
if (NewWidth != 7 && NewWidth != 15 && NewWidth != 31)
return nullptr;
// The width of the new add formed is 1 more than the bias.
++NewWidth;
// Check to see that CI1 is an all-ones value with NewWidth bits.
if (CI1->getBitWidth() == NewWidth ||
CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth))
return nullptr;
// This is only really a signed overflow check if the inputs have been
// sign-extended; check for that condition. For example, if CI2 is 2^31 and
// the operands of the add are 64 bits wide, we need at least 33 sign bits.
unsigned NeededSignBits = CI1->getBitWidth() - NewWidth + 1;
if (IC.ComputeNumSignBits(A, 0, &I) < NeededSignBits ||
IC.ComputeNumSignBits(B, 0, &I) < NeededSignBits)
return nullptr;
// In order to replace the original add with a narrower
// llvm.sadd.with.overflow, the only uses allowed are the add-with-constant
// and truncates that discard the high bits of the add. Verify that this is
// the case.
Instruction *OrigAdd = cast<Instruction>(AddWithCst->getOperand(0));
for (User *U : OrigAdd->users()) {
if (U == AddWithCst)
continue;
// Only accept truncates for now. We would really like a nice recursive
// predicate like SimplifyDemandedBits, but which goes downwards the use-def
// chain to see which bits of a value are actually demanded. If the
// original add had another add which was then immediately truncated, we
// could still do the transformation.
TruncInst *TI = dyn_cast<TruncInst>(U);
if (!TI || TI->getType()->getPrimitiveSizeInBits() > NewWidth)
return nullptr;
}
// If the pattern matches, truncate the inputs to the narrower type and
// use the sadd_with_overflow intrinsic to efficiently compute both the
// result and the overflow bit.
Type *NewType = IntegerType::get(OrigAdd->getContext(), NewWidth);
Value *F = Intrinsic::getDeclaration(I.getModule(),
Intrinsic::sadd_with_overflow, NewType);
InstCombiner::BuilderTy &Builder = IC.Builder;
// Put the new code above the original add, in case there are any uses of the
// add between the add and the compare.
Builder.SetInsertPoint(OrigAdd);
Value *TruncA = Builder.CreateTrunc(A, NewType, A->getName() + ".trunc");
Value *TruncB = Builder.CreateTrunc(B, NewType, B->getName() + ".trunc");
CallInst *Call = Builder.CreateCall(F, {TruncA, TruncB}, "sadd");
Value *Add = Builder.CreateExtractValue(Call, 0, "sadd.result");
Value *ZExt = Builder.CreateZExt(Add, OrigAdd->getType());
// The inner add was the result of the narrow add, zero extended to the
// wider type. Replace it with the result computed by the intrinsic.
IC.replaceInstUsesWith(*OrigAdd, ZExt);
// The original icmp gets replaced with the overflow value.
return ExtractValueInst::Create(Call, 1, "sadd.overflow");
}
// Fold icmp Pred X, C.
Instruction *InstCombiner::foldICmpWithConstant(ICmpInst &Cmp) {
CmpInst::Predicate Pred = Cmp.getPredicate();
Value *X = Cmp.getOperand(0);
const APInt *C;
if (!match(Cmp.getOperand(1), m_APInt(C)))
return nullptr;
Value *A = nullptr, *B = nullptr;
// Match the following pattern, which is a common idiom when writing
// overflow-safe integer arithmetic functions. The source performs an addition
// in wider type and explicitly checks for overflow using comparisons against
// INT_MIN and INT_MAX. Simplify by using the sadd_with_overflow intrinsic.
//
// TODO: This could probably be generalized to handle other overflow-safe
// operations if we worked out the formulas to compute the appropriate magic
// constants.
//
// sum = a + b
// if (sum+128 >u 255) ... -> llvm.sadd.with.overflow.i8
{
ConstantInt *CI2; // I = icmp ugt (add (add A, B), CI2), CI
if (Pred == ICmpInst::ICMP_UGT &&
match(X, m_Add(m_Add(m_Value(A), m_Value(B)), m_ConstantInt(CI2))))
if (Instruction *Res = processUGT_ADDCST_ADD(
Cmp, A, B, CI2, cast<ConstantInt>(Cmp.getOperand(1)), *this))
return Res;
}
// (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
if (C->isNullValue() && Pred == ICmpInst::ICMP_SGT) {
SelectPatternResult SPR = matchSelectPattern(X, A, B);
if (SPR.Flavor == SPF_SMIN) {
if (isKnownPositive(A, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, B, Cmp.getOperand(1));
if (isKnownPositive(B, DL, 0, &AC, &Cmp, &DT))
return new ICmpInst(Pred, A, Cmp.getOperand(1));
}
}
// FIXME: Use m_APInt to allow folds for splat constants.
ConstantInt *CI = dyn_cast<ConstantInt>(Cmp.getOperand(1));
if (!CI)
return nullptr;
// Canonicalize icmp instructions based on dominating conditions.
BasicBlock *Parent = Cmp.getParent();
BasicBlock *Dom = Parent->getSinglePredecessor();
auto *BI = Dom ? dyn_cast<BranchInst>(Dom->getTerminator()) : nullptr;
ICmpInst::Predicate Pred2;
BasicBlock *TrueBB, *FalseBB;
ConstantInt *CI2;
if (BI && match(BI, m_Br(m_ICmp(Pred2, m_Specific(X), m_ConstantInt(CI2)),
TrueBB, FalseBB)) &&
TrueBB != FalseBB) {
ConstantRange CR =
ConstantRange::makeAllowedICmpRegion(Pred, CI->getValue());
ConstantRange DominatingCR =
(Parent == TrueBB)
? ConstantRange::makeExactICmpRegion(Pred2, CI2->getValue())
: ConstantRange::makeExactICmpRegion(
CmpInst::getInversePredicate(Pred2), CI2->getValue());
ConstantRange Intersection = DominatingCR.intersectWith(CR);
ConstantRange Difference = DominatingCR.difference(CR);
if (Intersection.isEmptySet())
return replaceInstUsesWith(Cmp, Builder.getFalse());
if (Difference.isEmptySet())
return replaceInstUsesWith(Cmp, Builder.getTrue());
// If this is a normal comparison, it demands all bits. If it is a sign
// bit comparison, it only demands the sign bit.
bool UnusedBit;
bool IsSignBit = isSignBitCheck(Pred, CI->getValue(), UnusedBit);
// Canonicalizing a sign bit comparison that gets used in a branch,
// pessimizes codegen by generating branch on zero instruction instead
// of a test and branch. So we avoid canonicalizing in such situations
// because test and branch instruction has better branch displacement
// than compare and branch instruction.
if (Cmp.isEquality() || (IsSignBit && hasBranchUse(Cmp)))
return nullptr;
if (auto *AI = Intersection.getSingleElement())
return new ICmpInst(ICmpInst::ICMP_EQ, X, Builder.getInt(*AI));
if (auto *AD = Difference.getSingleElement())
return new ICmpInst(ICmpInst::ICMP_NE, X, Builder.getInt(*AD));
}
return nullptr;
}
/// Fold icmp (trunc X, Y), C.
Instruction *InstCombiner::foldICmpTruncConstant(ICmpInst &Cmp,
TruncInst *Trunc,
const APInt *C) {
ICmpInst::Predicate Pred = Cmp.getPredicate();
Value *X = Trunc->getOperand(0);
if (C->isOneValue() && C->getBitWidth() > 1) {
// icmp slt trunc(signum(V)) 1 --> icmp slt V, 1
Value *V = nullptr;
if (Pred == ICmpInst::ICMP_SLT && match(X, m_Signum(m_Value(V))))
return new ICmpInst(ICmpInst::ICMP_SLT, V,
ConstantInt::get(V->getType(), 1));
}
if (Cmp.isEquality() && Trunc->hasOneUse()) {
// Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42|highbits if all
// of the high bits truncated out of x are known.
unsigned DstBits = Trunc->getType()->getScalarSizeInBits(),
SrcBits = X->getType()->getScalarSizeInBits();
KnownBits Known = computeKnownBits(X, 0, &Cmp);
// If all the high bits are known, we can do this xform.
if ((Known.Zero | Known.One).countLeadingOnes() >= SrcBits - DstBits) {
// Pull in the high bits from known-ones set.
APInt NewRHS = C->zext(SrcBits);
NewRHS |= Known.One & APInt::getHighBitsSet(SrcBits, SrcBits - DstBits);
return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), NewRHS));
}
}
return nullptr;
}
/// Fold icmp (xor X, Y), C.
Instruction *InstCombiner::foldICmpXorConstant(ICmpInst &Cmp,
BinaryOperator *Xor,
const APInt *C) {
Value *X = Xor->getOperand(0);
Value *Y = Xor->getOperand(1);
const APInt *XorC;
if (!match(Y, m_APInt(XorC)))
return nullptr;
// If this is a comparison that tests the signbit (X < 0) or (x > -1),
// fold the xor.
ICmpInst::Predicate Pred = Cmp.getPredicate();
if ((Pred == ICmpInst::ICMP_SLT && C->isNullValue()) ||
(Pred == ICmpInst::ICMP_SGT && C->isAllOnesValue())) {
// If the sign bit of the XorCst is not set, there is no change to
// the operation, just stop using the Xor.
if (!XorC->isNegative()) {
Cmp.setOperand(0, X);
Worklist.Add(Xor);
return &Cmp;
}
// Was the old condition true if the operand is positive?
bool isTrueIfPositive = Pred == ICmpInst::ICMP_SGT;
// If so, the new one isn't.
isTrueIfPositive ^= true;
Constant *CmpConstant = cast<Constant>(Cmp.getOperand(1));
if (isTrueIfPositive)
return new ICmpInst(ICmpInst::ICMP_SGT, X, SubOne(CmpConstant));
else
return new ICmpInst(ICmpInst::ICMP_SLT, X, AddOne(CmpConstant));
}
if (Xor->hasOneUse()) {
// (icmp u/s (xor X SignMask), C) -> (icmp s/u X, (xor C SignMask))
if (!Cmp.isEquality() && XorC->isSignMask()) {
Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
: Cmp.getSignedPredicate();
return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), *C ^ *XorC));
}
// (icmp u/s (xor X ~SignMask), C) -> (icmp s/u X, (xor C ~SignMask))
if (!Cmp.isEquality() && XorC->isMaxSignedValue()) {
Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
: Cmp.getSignedPredicate();
Pred = Cmp.getSwappedPredicate(Pred);
return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), *C ^ *XorC));
}
}
// (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_UGT && *XorC == ~(*C) && (*C + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
// (icmp ult (xor X, C), -C) -> (icmp uge X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_ULT && *XorC == -(*C) && C->isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGE, X, Y);
return nullptr;
}
/// Fold icmp (and (sh X, Y), C2), C1.
Instruction *InstCombiner::foldICmpAndShift(ICmpInst &Cmp, BinaryOperator *And,
const APInt *C1, const APInt *C2) {
BinaryOperator *Shift = dyn_cast<BinaryOperator>(And->getOperand(0));
if (!Shift || !Shift->isShift())
return nullptr;
// If this is: (X >> C3) & C2 != C1 (where any shift and any compare could
// exist), turn it into (X & (C2 << C3)) != (C1 << C3). This happens a LOT in
// code produced by the clang front-end, for bitfield access.
// This seemingly simple opportunity to fold away a shift turns out to be
// rather complicated. See PR17827 for details.
unsigned ShiftOpcode = Shift->getOpcode();
bool IsShl = ShiftOpcode == Instruction::Shl;
const APInt *C3;
if (match(Shift->getOperand(1), m_APInt(C3))) {
bool CanFold = false;
if (ShiftOpcode == Instruction::AShr) {
// There may be some constraints that make this possible, but nothing
// simple has been discovered yet.
CanFold = false;
} else if (ShiftOpcode == Instruction::Shl) {
// For a left shift, we can fold if the comparison is not signed. We can
// also fold a signed comparison if the mask value and comparison value
// are not negative. These constraints may not be obvious, but we can
// prove that they are correct using an SMT solver.
if (!Cmp.isSigned() || (!C2->isNegative() && !C1->isNegative()))
CanFold = true;
} else if (ShiftOpcode == Instruction::LShr) {
// For a logical right shift, we can fold if the comparison is not signed.
// We can also fold a signed comparison if the shifted mask value and the
// shifted comparison value are not negative. These constraints may not be
// obvious, but we can prove that they are correct using an SMT solver.
if (!Cmp.isSigned() ||
(!C2->shl(*C3).isNegative() && !C1->shl(*C3).isNegative()))
CanFold = true;
}
if (CanFold) {
APInt NewCst = IsShl ? C1->lshr(*C3) : C1->shl(*C3);
APInt SameAsC1 = IsShl ? NewCst.shl(*C3) : NewCst.lshr(*C3);
// Check to see if we are shifting out any of the bits being compared.
if (SameAsC1 != *C1) {
// If we shifted bits out, the fold is not going to work out. As a
// special case, check to see if this means that the result is always
// true or false now.
if (Cmp.getPredicate() == ICmpInst::ICMP_EQ)
return replaceInstUsesWith(Cmp, ConstantInt::getFalse(Cmp.getType()));
if (Cmp.getPredicate() == ICmpInst::ICMP_NE)
return replaceInstUsesWith(Cmp, ConstantInt::getTrue(Cmp.getType()));
} else {
Cmp.setOperand(1, ConstantInt::get(And->getType(), NewCst));
APInt NewAndCst = IsShl ? C2->lshr(*C3) : C2->shl(*C3);
And->setOperand(1, ConstantInt::get(And->getType(), NewAndCst));
And->setOperand(0, Shift->getOperand(0));
Worklist.Add(Shift); // Shift is dead.
return &Cmp;
}
}
}
// Turn ((X >> Y) & C2) == 0 into (X & (C2 << Y)) == 0. The latter is
// preferable because it allows the C2 << Y expression to be hoisted out of a
// loop if Y is invariant and X is not.
if (Shift->hasOneUse() && C1->isNullValue() && Cmp.isEquality() &&
!Shift->isArithmeticShift() && !isa<Constant>(Shift->getOperand(0))) {
// Compute C2 << Y.
Value *NewShift =
IsShl ? Builder.CreateLShr(And->getOperand(1), Shift->getOperand(1))
: Builder.CreateShl(And->getOperand(1), Shift->getOperand(1));
// Compute X & (C2 << Y).
Value *NewAnd = Builder.CreateAnd(Shift->getOperand(0), NewShift);
Cmp.setOperand(0, NewAnd);
return &Cmp;
}
return nullptr;
}
/// Fold icmp (and X, C2), C1.
Instruction *InstCombiner::foldICmpAndConstConst(ICmpInst &Cmp,
BinaryOperator *And,
const APInt *C1) {
const APInt *C2;
if (!match(And->getOperand(1), m_APInt(C2)))
return nullptr;
if (!And->hasOneUse() || !And->getOperand(0)->hasOneUse())
return nullptr;
// If the LHS is an 'and' of a truncate and we can widen the and/compare to
// the input width without changing the value produced, eliminate the cast:
//
// icmp (and (trunc W), C2), C1 -> icmp (and W, C2'), C1'
//
// We can do this transformation if the constants do not have their sign bits
// set or if it is an equality comparison. Extending a relational comparison
// when we're checking the sign bit would not work.
Value *W;
if (match(And->getOperand(0), m_Trunc(m_Value(W))) &&
(Cmp.isEquality() || (!C1->isNegative() && !C2->isNegative()))) {
// TODO: Is this a good transform for vectors? Wider types may reduce
// throughput. Should this transform be limited (even for scalars) by using
// shouldChangeType()?
if (!Cmp.getType()->isVectorTy()) {
Type *WideType = W->getType();
unsigned WideScalarBits = WideType->getScalarSizeInBits();
Constant *ZextC1 = ConstantInt::get(WideType, C1->zext(WideScalarBits));
Constant *ZextC2 = ConstantInt::get(WideType, C2->zext(WideScalarBits));
Value *NewAnd = Builder.CreateAnd(W, ZextC2, And->getName());
return new ICmpInst(Cmp.getPredicate(), NewAnd, ZextC1);
}
}
if (Instruction *I = foldICmpAndShift(Cmp, And, C1, C2))
return I;
// (icmp pred (and (or (lshr A, B), A), 1), 0) -->
// (icmp pred (and A, (or (shl 1, B), 1), 0))
//
// iff pred isn't signed
if (!Cmp.isSigned() && C1->isNullValue() &&
match(And->getOperand(1), m_One())) {
Constant *One = cast<Constant>(And->getOperand(1));
Value *Or = And->getOperand(0);
Value *A, *B, *LShr;
if (match(Or, m_Or(m_Value(LShr), m_Value(A))) &&
match(LShr, m_LShr(m_Specific(A), m_Value(B)))) {
unsigned UsesRemoved = 0;
if (And->hasOneUse())
++UsesRemoved;
if (Or->hasOneUse())
++UsesRemoved;
if (LShr->hasOneUse())
++UsesRemoved;
// Compute A & ((1 << B) | 1)
Value *NewOr = nullptr;
if (auto *C = dyn_cast<Constant>(B)) {
if (UsesRemoved >= 1)
NewOr = ConstantExpr::getOr(ConstantExpr::getNUWShl(One, C), One);
} else {
if (UsesRemoved >= 3)
NewOr = Builder.CreateOr(Builder.CreateShl(One, B, LShr->getName(),
/*HasNUW=*/true),
One, Or->getName());
}
if (NewOr) {
Value *NewAnd = Builder.CreateAnd(A, NewOr, And->getName());
Cmp.setOperand(0, NewAnd);
return &Cmp;
}
}
}
// (X & C2) > C1 --> (X & C2) != 0, if any bit set in (X & C2) will produce a
// result greater than C1.
unsigned NumTZ = C2->countTrailingZeros();
if (Cmp.getPredicate() == ICmpInst::ICMP_UGT && NumTZ < C2->getBitWidth() &&
APInt::getOneBitSet(C2->getBitWidth(), NumTZ).ugt(*C1)) {
Constant *Zero = Constant::getNullValue(And->getType());
return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
}
return nullptr;
}
/// Fold icmp (and X, Y), C.
Instruction *InstCombiner::foldICmpAndConstant(ICmpInst &Cmp,
BinaryOperator *And,
const APInt *C) {
if (Instruction *I = foldICmpAndConstConst(Cmp, And, C))
return I;
// TODO: These all require that Y is constant too, so refactor with the above.
// Try to optimize things like "A[i] & 42 == 0" to index computations.
Value *X = And->getOperand(0);
Value *Y = And->getOperand(1);
if (auto *LI = dyn_cast<LoadInst>(X))
if (auto *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0)))
if (auto *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
!LI->isVolatile() && isa<ConstantInt>(Y)) {
ConstantInt *C2 = cast<ConstantInt>(Y);
if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, Cmp, C2))
return Res;
}
if (!Cmp.isEquality())
return nullptr;
// X & -C == -C -> X > u ~C
// X & -C != -C -> X <= u ~C
// iff C is a power of 2
if (Cmp.getOperand(1) == Y && (-(*C)).isPowerOf2()) {
auto NewPred = Cmp.getPredicate() == CmpInst::ICMP_EQ ? CmpInst::ICMP_UGT
: CmpInst::ICMP_ULE;
return new ICmpInst(NewPred, X, SubOne(cast<Constant>(Cmp.getOperand(1))));
}
// (X & C2) == 0 -> (trunc X) >= 0
// (X & C2) != 0 -> (trunc X) < 0
// iff C2 is a power of 2 and it masks the sign bit of a legal integer type.
const APInt *C2;
if (And->hasOneUse() && C->isNullValue() && match(Y, m_APInt(C2))) {
int32_t ExactLogBase2 = C2->exactLogBase2();
if (ExactLogBase2 != -1 && DL.isLegalInteger(ExactLogBase2 + 1)) {
Type *NTy = IntegerType::get(Cmp.getContext(), ExactLogBase2 + 1);
if (And->getType()->isVectorTy())
NTy = VectorType::get(NTy, And->getType()->getVectorNumElements());
Value *Trunc = Builder.CreateTrunc(X, NTy);
auto NewPred = Cmp.getPredicate() == CmpInst::ICMP_EQ ? CmpInst::ICMP_SGE
: CmpInst::ICMP_SLT;
return new ICmpInst(NewPred, Trunc, Constant::getNullValue(NTy));
}
}
return nullptr;
}
/// Fold icmp (or X, Y), C.
Instruction *InstCombiner::foldICmpOrConstant(ICmpInst &Cmp, BinaryOperator *Or,
const APInt *C) {
ICmpInst::Predicate Pred = Cmp.getPredicate();
if (C->isOneValue()) {
// icmp slt signum(V) 1 --> icmp slt V, 1
Value *V = nullptr;
if (Pred == ICmpInst::ICMP_SLT && match(Or, m_Signum(m_Value(V))))
return new ICmpInst(ICmpInst::ICMP_SLT, V,
ConstantInt::get(V->getType(), 1));
}
// X | C == C --> X <=u C
// X | C != C --> X >u C
// iff C+1 is a power of 2 (C is a bitmask of the low bits)
if (Cmp.isEquality() && Cmp.getOperand(1) == Or->getOperand(1) &&
(*C + 1).isPowerOf2()) {
Pred = (Pred == CmpInst::ICMP_EQ) ? CmpInst::ICMP_ULE : CmpInst::ICMP_UGT;
return new ICmpInst(Pred, Or->getOperand(0), Or->getOperand(1));
}
if (!Cmp.isEquality() || !C->isNullValue() || !Or->hasOneUse())
return nullptr;
Value *P, *Q;
if (match(Or, m_Or(m_PtrToInt(m_Value(P)), m_PtrToInt(m_Value(Q))))) {
// Simplify icmp eq (or (ptrtoint P), (ptrtoint Q)), 0
// -> and (icmp eq P, null), (icmp eq Q, null).
Value *CmpP =
Builder.CreateICmp(Pred, P, ConstantInt::getNullValue(P->getType()));
Value *CmpQ =
Builder.CreateICmp(Pred, Q, ConstantInt::getNullValue(Q->getType()));
auto BOpc = Pred == CmpInst::ICMP_EQ ? Instruction::And : Instruction::Or;
return BinaryOperator::Create(BOpc, CmpP, CmpQ);
}
// Are we using xors to bitwise check for a pair of (in)equalities? Convert to
// a shorter form that has more potential to be folded even further.
Value *X1, *X2, *X3, *X4;
if (match(Or->getOperand(0), m_OneUse(m_Xor(m_Value(X1), m_Value(X2)))) &&
match(Or->getOperand(1), m_OneUse(m_Xor(m_Value(X3), m_Value(X4))))) {
// ((X1 ^ X2) || (X3 ^ X4)) == 0 --> (X1 == X2) && (X3 == X4)
// ((X1 ^ X2) || (X3 ^ X4)) != 0 --> (X1 != X2) || (X3 != X4)
Value *Cmp12 = Builder.CreateICmp(Pred, X1, X2);
Value *Cmp34 = Builder.CreateICmp(Pred, X3, X4);
auto BOpc = Pred == CmpInst::ICMP_EQ ? Instruction::And : Instruction::Or;
return BinaryOperator::Create(BOpc, Cmp12, Cmp34);
}
return nullptr;
}
/// Fold icmp (mul X, Y), C.
Instruction *InstCombiner::foldICmpMulConstant(ICmpInst &Cmp,
BinaryOperator *Mul,
const APInt *C) {
const APInt *MulC;
if (!match(Mul->getOperand(1), m_APInt(MulC)))
return nullptr;
// If this is a test of the sign bit and the multiply is sign-preserving with
// a constant operand, use the multiply LHS operand instead.
ICmpInst::Predicate Pred = Cmp.getPredicate();
if (isSignTest(Pred, *C) && Mul->hasNoSignedWrap()) {
if (MulC->isNegative())
Pred = ICmpInst::getSwappedPredicate(Pred);
return new ICmpInst(Pred, Mul->getOperand(0),
Constant::getNullValue(Mul->getType()));
}
return nullptr;
}
/// Fold icmp (shl 1, Y), C.
static Instruction *foldICmpShlOne(ICmpInst &Cmp, Instruction *Shl,
const APInt *C) {
Value *Y;
if (!match(Shl, m_Shl(m_One(), m_Value(Y))))
return nullptr;
Type *ShiftType = Shl->getType();
uint32_t TypeBits = C->getBitWidth();
bool CIsPowerOf2 = C->isPowerOf2();
ICmpInst::Predicate Pred = Cmp.getPredicate();
if (Cmp.isUnsigned()) {
// (1 << Y) pred C -> Y pred Log2(C)
if (!CIsPowerOf2) {
// (1 << Y) < 30 -> Y <= 4
// (1 << Y) <= 30 -> Y <= 4
// (1 << Y) >= 30 -> Y > 4
// (1 << Y) > 30 -> Y > 4
if (Pred == ICmpInst::ICMP_ULT)
Pred = ICmpInst::ICMP_ULE;
else if (Pred == ICmpInst::ICMP_UGE)
Pred = ICmpInst::ICMP_UGT;
}
// (1 << Y) >= 2147483648 -> Y >= 31 -> Y == 31
// (1 << Y) < 2147483648 -> Y < 31 -> Y != 31
unsigned CLog2 = C->logBase2();
if (CLog2 == TypeBits - 1) {
if (Pred == ICmpInst::ICMP_UGE)
Pred = ICmpInst::ICMP_EQ;
else if (Pred == ICmpInst::ICMP_ULT)
Pred = ICmpInst::ICMP_NE;
}
return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, CLog2));
} else if (Cmp.isSigned()) {
Constant *BitWidthMinusOne = ConstantInt::get(ShiftType, TypeBits - 1);
if (C->isAllOnesValue()) {
// (1 << Y) <= -1 -> Y == 31
if (Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
// (1 << Y) > -1 -> Y != 31
if (Pred == ICmpInst::ICMP_SGT)
return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
} else if (!(*C)) {
// (1 << Y) < 0 -> Y == 31
// (1 << Y) <= 0 -> Y == 31
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
// (1 << Y) >= 0 -> Y != 31
// (1 << Y) > 0 -> Y != 31
if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
}
} else if (Cmp.isEquality() && CIsPowerOf2) {
return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, C->logBase2()));
}
return nullptr;
}
/// Fold icmp (shl X, Y), C.
Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
BinaryOperator *Shl,
const APInt *C) {
const APInt *ShiftVal;
if (Cmp.isEquality() && match(Shl->getOperand(0), m_APInt(ShiftVal)))
return foldICmpShlConstConst(Cmp, Shl->getOperand(1), *C, *ShiftVal);
const APInt *ShiftAmt;
if (!match(Shl->getOperand(1), m_APInt(ShiftAmt)))
return foldICmpShlOne(Cmp, Shl, C);
// Check that the shift amount is in range. If not, don't perform undefined
// shifts. When the shift is visited, it will be simplified.
unsigned TypeBits = C->getBitWidth();
if (ShiftAmt->uge(TypeBits))
return nullptr;
ICmpInst::Predicate Pred = Cmp.getPredicate();
Value *X = Shl->getOperand(0);
Type *ShType = Shl->getType();
// NSW guarantees that we are only shifting out sign bits from the high bits,
// so we can ASHR the compare constant without needing a mask and eliminate
// the shift.
if (Shl->hasNoSignedWrap()) {
if (Pred == ICmpInst::ICMP_SGT) {
// icmp Pred (shl nsw X, ShiftAmt), C --> icmp Pred X, (C >>s ShiftAmt)
APInt ShiftedC = C->ashr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) {
// This is the same code as the SGT case, but assert the pre-condition
// that is needed for this to work with equality predicates.
assert(C->ashr(*ShiftAmt).shl(*ShiftAmt) == *C &&
"Compare known true or false was not folded");
APInt ShiftedC = C->ashr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_SLT) {
// SLE is the same as above, but SLE is canonicalized to SLT, so convert:
// (X << S) <=s C is equiv to X <=s (C >> S) for all C
// (X << S) <s (C + 1) is equiv to X <s (C >> S) + 1 if C <s SMAX
// (X << S) <s C is equiv to X <s ((C - 1) >> S) + 1 if C >s SMIN
assert(!C->isMinSignedValue() && "Unexpected icmp slt");
APInt ShiftedC = (*C - 1).ashr(*ShiftAmt) + 1;
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
// If this is a signed comparison to 0 and the shift is sign preserving,
// use the shift LHS operand instead; isSignTest may change 'Pred', so only
// do that if we're sure to not continue on in this function.
if (isSignTest(Pred, *C))
return new ICmpInst(Pred, X, Constant::getNullValue(ShType));
}
// NUW guarantees that we are only shifting out zero bits from the high bits,
// so we can LSHR the compare constant without needing a mask and eliminate
// the shift.
if (Shl->hasNoUnsignedWrap()) {
if (Pred == ICmpInst::ICMP_UGT) {
// icmp Pred (shl nuw X, ShiftAmt), C --> icmp Pred X, (C >>u ShiftAmt)
APInt ShiftedC = C->lshr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) {
// This is the same code as the UGT case, but assert the pre-condition
// that is needed for this to work with equality predicates.
assert(C->lshr(*ShiftAmt).shl(*ShiftAmt) == *C &&
"Compare known true or false was not folded");
APInt ShiftedC = C->lshr(*ShiftAmt);
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
if (Pred == ICmpInst::ICMP_ULT) {
// ULE is the same as above, but ULE is canonicalized to ULT, so convert:
// (X << S) <=u C is equiv to X <=u (C >> S) for all C
// (X << S) <u (C + 1) is equiv to X <u (C >> S) + 1 if C <u ~0u
// (X << S) <u C is equiv to X <u ((C - 1) >> S) + 1 if C >u 0
assert(C->ugt(0) && "ult 0 should have been eliminated");
APInt ShiftedC = (*C - 1).lshr(*ShiftAmt) + 1;
return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
}
}
if (Cmp.isEquality() && Shl->hasOneUse()) {
// Strength-reduce the shift into an 'and'.
Constant *Mask = ConstantInt::get(
ShType,
APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt->getZExtValue()));
Value *And = Builder.CreateAnd(X, Mask, Shl->getName() + ".mask");
Constant *LShrC = ConstantInt::get(ShType, C->lshr(*ShiftAmt));
return new ICmpInst(Pred, And, LShrC);
}
// Otherwise, if this is a comparison of the sign bit, simplify to and/test.
bool TrueIfSigned = false;
if (Shl->hasOneUse() && isSignBitCheck(Pred, *C, TrueIfSigned)) {
// (X << 31) <s 0 --> (X & 1) != 0
Constant *Mask = ConstantInt::get(
ShType,
APInt::getOneBitSet(TypeBits, TypeBits - ShiftAmt->getZExtValue() - 1));
Value *And = Builder.CreateAnd(X, Mask, Shl->getName() + ".mask");
return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
And, Constant::getNullValue(ShType));
}
// Transform (icmp pred iM (shl iM %v, N), C)
// -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))
// Transform the shl to a trunc if (trunc (C>>N)) has no loss and M-N.
// This enables us to get rid of the shift in favor of a trunc that may be
// free on the target. It has the additional benefit of comparing to a
// smaller constant that may be more target-friendly.
unsigned Amt = ShiftAmt->getLimitedValue(TypeBits - 1);
if (Shl->hasOneUse() && Amt != 0 && C->countTrailingZeros() >= Amt &&
DL.isLegalInteger(TypeBits - Amt)) {
Type *TruncTy = IntegerType::get(Cmp.getContext(), TypeBits - Amt);
if (ShType->isVectorTy())
TruncTy = VectorType::get(TruncTy, ShType->getVectorNumElements());
Constant *NewC =
ConstantInt::get(TruncTy, C->ashr(*ShiftAmt).trunc(TypeBits - Amt));
return new ICmpInst(Pred, Builder.CreateTrunc(X, TruncTy), NewC);
}
return nullptr;
}
/// Fold icmp ({al}shr X, Y), C.
Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp,
BinaryOperator *Shr,
const APInt *C) {
// An exact shr only shifts out zero bits, so:
// icmp eq/ne (shr X, Y), 0 --> icmp eq/ne X, 0
Value *X = Shr->getOperand(0);
CmpInst::Predicate Pred = Cmp.getPredicate();
if (Cmp.isEquality() && Shr->isExact() && Shr->hasOneUse() &&
C->isNullValue())
return new ICmpInst(Pred, X, Cmp.getOperand(1));
const APInt *ShiftVal;
if (Cmp.isEquality() && match(Shr->getOperand(0), m_APInt(ShiftVal)))
return foldICmpShrConstConst(Cmp, Shr->getOperand(1), *C, *ShiftVal);
const APInt *ShiftAmt;
if (!match(Shr->getOperand(1), m_APInt(ShiftAmt)))
return nullptr;
// Check that the shift amount is in range. If not, don't perform undefined
// shifts. When the shift is visited it will be simplified.
unsigned TypeBits = C->getBitWidth();
unsigned ShAmtVal = ShiftAmt->getLimitedValue(TypeBits);
if (ShAmtVal >= TypeBits || ShAmtVal == 0)
return nullptr;
bool IsAShr = Shr->getOpcode() == Instruction::AShr;
if (!Cmp.isEquality()) {
// If we have an unsigned comparison and an ashr, we can't simplify this.
// Similarly for signed comparisons with lshr.
if (Cmp.isSigned() != IsAShr)
return nullptr;
// Otherwise, all lshr and most exact ashr's are equivalent to a udiv/sdiv
// by a power of 2. Since we already have logic to simplify these,
// transform to div and then simplify the resultant comparison.
if (IsAShr && (!Shr->isExact() || ShAmtVal == TypeBits - 1))
return nullptr;
// Revisit the shift (to delete it).
Worklist.Add(Shr);
Constant *DivCst = ConstantInt::get(
Shr->getType(), APInt::getOneBitSet(TypeBits, ShAmtVal));
Value *Tmp = IsAShr ? Builder.CreateSDiv(X, DivCst, "", Shr->isExact())
: Builder.CreateUDiv(X, DivCst, "", Shr->isExact());
Cmp.setOperand(0, Tmp);
// If the builder folded the binop, just return it.
BinaryOperator *TheDiv = dyn_cast<BinaryOperator>(Tmp);
if (!TheDiv)
return &Cmp;
// Otherwise, fold this div/compare.
assert(TheDiv->getOpcode() == Instruction::SDiv ||
TheDiv->getOpcode() == Instruction::UDiv);
Instruction *Res = foldICmpDivConstant(Cmp, TheDiv, C);
assert(Res && "This div/cst should have folded!");
return Res;
}
// Handle equality comparisons of shift-by-constant.
// If the comparison constant changes with the shift, the comparison cannot
// succeed (bits of the comparison constant cannot match the shifted value).
// This should be known by InstSimplify and already be folded to true/false.
assert(((IsAShr && C->shl(ShAmtVal).ashr(ShAmtVal) == *C) ||
(!IsAShr && C->shl(ShAmtVal).lshr(ShAmtVal) == *C)) &&
"Expected icmp+shr simplify did not occur.");
// Check if the bits shifted out are known to be zero. If so, we can compare
// against the unshifted value:
// (X & 4) >> 1 == 2 --> (X & 4) == 4.
Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), *C << ShAmtVal);
if (Shr->hasOneUse()) {
if (Shr->isExact())
return new ICmpInst(Pred, X, ShiftedCmpRHS);
// Otherwise strength reduce the shift into an 'and'.
APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
Constant *Mask = ConstantInt::get(Shr->getType(), Val);
Value *And = Builder.CreateAnd(X, Mask, Shr->getName() + ".mask");
return new ICmpInst(Pred, And, ShiftedCmpRHS);
}
return nullptr;
}
/// Fold icmp (udiv X, Y), C.
Instruction *InstCombiner::foldICmpUDivConstant(ICmpInst &Cmp,
BinaryOperator *UDiv,
const APInt *C) {
const APInt *C2;
if (!match(UDiv->getOperand(0), m_APInt(C2)))
return nullptr;
assert(*C2 != 0 && "udiv 0, X should have been simplified already.");
// (icmp ugt (udiv C2, Y), C) -> (icmp ule Y, C2/(C+1))
Value *Y = UDiv->getOperand(1);
if (Cmp.getPredicate() == ICmpInst::ICMP_UGT) {
assert(!C->isMaxValue() &&
"icmp ugt X, UINT_MAX should have been simplified already.");
return new ICmpInst(ICmpInst::ICMP_ULE, Y,
ConstantInt::get(Y->getType(), C2->udiv(*C + 1)));
}
// (icmp ult (udiv C2, Y), C) -> (icmp ugt Y, C2/C)
if (Cmp.getPredicate() == ICmpInst::ICMP_ULT) {
assert(*C != 0 && "icmp ult X, 0 should have been simplified already.");
return new ICmpInst(ICmpInst::ICMP_UGT, Y,
ConstantInt::get(Y->getType(), C2->udiv(*C)));
}
return nullptr;
}
/// Fold icmp ({su}div X, Y), C.
Instruction *InstCombiner::foldICmpDivConstant(ICmpInst &Cmp,
BinaryOperator *Div,
const APInt *C) {
// Fold: icmp pred ([us]div X, C2), C -> range test
// Fold this div into the comparison, producing a range check.
// Determine, based on the divide type, what the range is being
// checked. If there is an overflow on the low or high side, remember
// it, otherwise compute the range [low, hi) bounding the new value.
// See: InsertRangeTest above for the kinds of replacements possible.
const APInt *C2;
if (!match(Div->getOperand(1), m_APInt(C2)))
return nullptr;
// FIXME: If the operand types don't match the type of the divide
// then don't attempt this transform. The code below doesn't have the
// logic to deal with a signed divide and an unsigned compare (and
// vice versa). This is because (x /s C2) <s C produces different
// results than (x /s C2) <u C or (x /u C2) <s C or even
// (x /u C2) <u C. Simply casting the operands and result won't
// work. :( The if statement below tests that condition and bails
// if it finds it.
bool DivIsSigned = Div->getOpcode() == Instruction::SDiv;
if (!Cmp.isEquality() && DivIsSigned != Cmp.isSigned())
return nullptr;
// The ProdOV computation fails on divide by 0 and divide by -1. Cases with
// INT_MIN will also fail if the divisor is 1. Although folds of all these
// division-by-constant cases should be present, we can not assert that they
// have happened before we reach this icmp instruction.
if (C2->isNullValue() || C2->isOneValue() ||
(DivIsSigned && C2->isAllOnesValue()))
return nullptr;
// TODO: We could do all of the computations below using APInt.
Constant *CmpRHS = cast<Constant>(Cmp.getOperand(1));
Constant *DivRHS = cast<Constant>(Div->getOperand(1));
// Compute Prod = CmpRHS * DivRHS. We are essentially solving an equation of
// form X / C2 = C. We solve for X by multiplying C2 (DivRHS) and C (CmpRHS).
// By solving for X, we can turn this into a range check instead of computing
// a divide.
Constant *Prod = ConstantExpr::getMul(CmpRHS, DivRHS);
// Determine if the product overflows by seeing if the product is not equal to
// the divide. Make sure we do the same kind of divide as in the LHS
// instruction that we're folding.
bool ProdOV = (DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS)
: ConstantExpr::getUDiv(Prod, DivRHS)) != CmpRHS;
ICmpInst::Predicate Pred = Cmp.getPredicate();
// If the division is known to be exact, then there is no remainder from the
// divide, so the covered range size is unit, otherwise it is the divisor.
Constant *RangeSize =
Div->isExact() ? ConstantInt::get(Div->getType(), 1) : DivRHS;
// Figure out the interval that is being checked. For example, a comparison
// like "X /u 5 == 0" is really checking that X is in the interval [0, 5).
// Compute this interval based on the constants involved and the signedness of
// the compare/divide. This computes a half-open interval, keeping track of
// whether either value in the interval overflows. After analysis each
// overflow variable is set to 0 if it's corresponding bound variable is valid
// -1 if overflowed off the bottom end, or +1 if overflowed off the top end.
int LoOverflow = 0, HiOverflow = 0;
Constant *LoBound = nullptr, *HiBound = nullptr;
if (!DivIsSigned) { // udiv
// e.g. X/5 op 3 --> [15, 20)
LoBound = Prod;
HiOverflow = LoOverflow = ProdOV;
if (!HiOverflow) {
// If this is not an exact divide, then many values in the range collapse
// to the same result value.
HiOverflow = addWithOverflow(HiBound, LoBound, RangeSize, false);
}
} else if (C2->isStrictlyPositive()) { // Divisor is > 0.
if (C->isNullValue()) { // (X / pos) op 0
// Can't overflow. e.g. X/2 op 0 --> [-1, 2)
LoBound = ConstantExpr::getNeg(SubOne(RangeSize));
HiBound = RangeSize;
} else if (C->isStrictlyPositive()) { // (X / pos) op pos
LoBound = Prod; // e.g. X/5 op 3 --> [15, 20)
HiOverflow = LoOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = addWithOverflow(HiBound, Prod, RangeSize, true);
} else { // (X / pos) op neg
// e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14)
HiBound = AddOne(Prod);
LoOverflow = HiOverflow = ProdOV ? -1 : 0;
if (!LoOverflow) {
Constant *DivNeg = ConstantExpr::getNeg(RangeSize);
LoOverflow = addWithOverflow(LoBound, HiBound, DivNeg, true) ? -1 : 0;
}
}
} else if (C2->isNegative()) { // Divisor is < 0.
if (Div->isExact())
RangeSize = ConstantExpr::getNeg(RangeSize);
if (C->isNullValue()) { // (X / neg) op 0
// e.g. X/-5 op 0 --> [-4, 5)
LoBound = AddOne(RangeSize);
HiBound = ConstantExpr::getNeg(RangeSize);
if (HiBound == DivRHS) { // -INTMIN = INTMIN
HiOverflow = 1; // [INTMIN+1, overflow)
HiBound = nullptr; // e.g. X/INTMIN = 0 --> X > INTMIN
}
} else if (C->isStrictlyPositive()) { // (X / neg) op pos
// e.g. X/-5 op 3 --> [-19, -14)
HiBound = AddOne(Prod);
HiOverflow = LoOverflow = ProdOV ? -1 : 0;
if (!LoOverflow)
LoOverflow = addWithOverflow(LoBound, HiBound, RangeSize, true) ? -1:0;
} else { // (X / neg) op neg
LoBound = Prod; // e.g. X/-5 op -3 --> [15, 20)
LoOverflow = HiOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = subWithOverflow(HiBound, Prod, RangeSize, true);
}
// Dividing by a negative swaps the condition. LT <-> GT
Pred = ICmpInst::getSwappedPredicate(Pred);
}
Value *X = Div->getOperand(0);
switch (Pred) {
default: llvm_unreachable("Unhandled icmp opcode!");
case ICmpInst::ICMP_EQ:
if (LoOverflow && HiOverflow)
return replaceInstUsesWith(Cmp, Builder.getFalse());
if (HiOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
ICmpInst::ICMP_UGE, X, LoBound);
if (LoOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
ICmpInst::ICMP_ULT, X, HiBound);
return replaceInstUsesWith(
Cmp, insertRangeTest(X, LoBound->getUniqueInteger(),
HiBound->getUniqueInteger(), DivIsSigned, true));
case ICmpInst::ICMP_NE:
if (LoOverflow && HiOverflow)
return replaceInstUsesWith(Cmp, Builder.getTrue());
if (HiOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
ICmpInst::ICMP_ULT, X, LoBound);
if (LoOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
ICmpInst::ICMP_UGE, X, HiBound);
return replaceInstUsesWith(Cmp,
insertRangeTest(X, LoBound->getUniqueInteger(),
HiBound->getUniqueInteger(),
DivIsSigned, false));
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT:
if (LoOverflow == +1) // Low bound is greater than input range.
return replaceInstUsesWith(Cmp, Builder.getTrue());
if (LoOverflow == -1) // Low bound is less than input range.
return replaceInstUsesWith(Cmp, Builder.getFalse());
return new ICmpInst(Pred, X, LoBound);
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
if (HiOverflow == +1) // High bound greater than input range.
return replaceInstUsesWith(Cmp, Builder.getFalse());
if (HiOverflow == -1) // High bound less than input range.
return replaceInstUsesWith(Cmp, Builder.getTrue());
if (Pred == ICmpInst::ICMP_UGT)
return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound);
return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound);
}
return nullptr;
}
/// Fold icmp (sub X, Y), C.
Instruction *InstCombiner::foldICmpSubConstant(ICmpInst &Cmp,
BinaryOperator *Sub,
const APInt *C) {
Value *X = Sub->getOperand(0), *Y = Sub->getOperand(1);
ICmpInst::Predicate Pred = Cmp.getPredicate();
// The following transforms are only worth it if the only user of the subtract
// is the icmp.
if (!Sub->hasOneUse())
return nullptr;
if (Sub->hasNoSignedWrap()) {
// (icmp sgt (sub nsw X, Y), -1) -> (icmp sge X, Y)
if (Pred == ICmpInst::ICMP_SGT && C->isAllOnesValue())
return new ICmpInst(ICmpInst::ICMP_SGE, X, Y);
// (icmp sgt (sub nsw X, Y), 0) -> (icmp sgt X, Y)
if (Pred == ICmpInst::ICMP_SGT && C->isNullValue())
return new ICmpInst(ICmpInst::ICMP_SGT, X, Y);
// (icmp slt (sub nsw X, Y), 0) -> (icmp slt X, Y)
if (Pred == ICmpInst::ICMP_SLT && C->isNullValue())
return new ICmpInst(ICmpInst::ICMP_SLT, X, Y);
// (icmp slt (sub nsw X, Y), 1) -> (icmp sle X, Y)
if (Pred == ICmpInst::ICMP_SLT && C->isOneValue())
return new ICmpInst(ICmpInst::ICMP_SLE, X, Y);
}
const APInt *C2;
if (!match(X, m_APInt(C2)))
return nullptr;
// C2 - Y <u C -> (Y | (C - 1)) == C2
// iff (C2 & (C - 1)) == C - 1 and C is a power of 2
if (Pred == ICmpInst::ICMP_ULT && C->isPowerOf2() &&
(*C2 & (*C - 1)) == (*C - 1))
return new ICmpInst(ICmpInst::ICMP_EQ, Builder.CreateOr(Y, *C - 1), X);
// C2 - Y >u C -> (Y | C) != C2
// iff C2 & C == C and C + 1 is a power of 2
if (Pred == ICmpInst::ICMP_UGT && (*C + 1).isPowerOf2() && (*C2 & *C) == *C)
return new ICmpInst(ICmpInst::ICMP_NE, Builder.CreateOr(Y, *C), X);
return nullptr;
}
/// Fold icmp (add X, Y), C.
Instruction *InstCombiner::foldICmpAddConstant(ICmpInst &Cmp,
BinaryOperator *Add,
const APInt *C) {
Value *Y = Add->getOperand(1);
const APInt *C2;
if (Cmp.isEquality() || !match(Y, m_APInt(C2)))
return nullptr;
// Fold icmp pred (add X, C2), C.
Value *X = Add->getOperand(0);
Type *Ty = Add->getType();
CmpInst::Predicate Pred = Cmp.getPredicate();
// If the add does not wrap, we can always adjust the compare by subtracting
// the constants. Equality comparisons are handled elsewhere. SGE/SLE are
// canonicalized to SGT/SLT.
if (Add->hasNoSignedWrap() &&
(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SLT)) {
bool Overflow;
APInt NewC = C->ssub_ov(*C2, Overflow);
// If there is overflow, the result must be true or false.
// TODO: Can we assert there is no overflow because InstSimplify always
// handles those cases?
if (!Overflow)
// icmp Pred (add nsw X, C2), C --> icmp Pred X, (C - C2)
return new ICmpInst(Pred, X, ConstantInt::get(Ty, NewC));
}
auto CR = ConstantRange::makeExactICmpRegion(Pred, *C).subtract(*C2);
const APInt &Upper = CR.getUpper();
const APInt &Lower = CR.getLower();
if (Cmp.isSigned()) {
if (Lower.isSignMask())
return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantInt::get(Ty, Upper));
if (Upper.isSignMask())
return new ICmpInst(ICmpInst::ICMP_SGE, X, ConstantInt::get(Ty, Lower));
} else {
if (Lower.isMinValue())
return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantInt::get(Ty, Upper));
if (Upper.isMinValue())
return new ICmpInst(ICmpInst::ICMP_UGE, X, ConstantInt::get(Ty, Lower));
}
if (!Add->hasOneUse())
return nullptr;
// X+C <u C2 -> (X & -C2) == C
// iff C & (C2-1) == 0
// C2 is a power of 2
if (Pred == ICmpInst::ICMP_ULT && C->isPowerOf2() && (*C2 & (*C - 1)) == 0)
return new ICmpInst(ICmpInst::ICMP_EQ, Builder.CreateAnd(X, -(*C)),
ConstantExpr::getNeg(cast<Constant>(Y)));
// X+C >u C2 -> (X & ~C2) != C
// iff C & C2 == 0
// C2+1 is a power of 2
if (Pred == ICmpInst::ICMP_UGT && (*C + 1).isPowerOf2() && (*C2 & *C) == 0)
return new ICmpInst(ICmpInst::ICMP_NE, Builder.CreateAnd(X, ~(*C)),
ConstantExpr::getNeg(cast<Constant>(Y)));
return nullptr;
}
bool InstCombiner::matchThreeWayIntCompare(SelectInst *SI, Value *&LHS,
Value *&RHS, ConstantInt *&Less,
ConstantInt *&Equal,
ConstantInt *&Greater) {
// TODO: Generalize this to work with other comparison idioms or ensure
// they get canonicalized into this form.
// select i1 (a == b), i32 Equal, i32 (select i1 (a < b), i32 Less, i32
// Greater), where Equal, Less and Greater are placeholders for any three
// constants.
ICmpInst::Predicate PredA, PredB;
if (match(SI->getTrueValue(), m_ConstantInt(Equal)) &&
match(SI->getCondition(), m_ICmp(PredA, m_Value(LHS), m_Value(RHS))) &&
PredA == ICmpInst::ICMP_EQ &&
match(SI->getFalseValue(),
m_Select(m_ICmp(PredB, m_Specific(LHS), m_Specific(RHS)),
m_ConstantInt(Less), m_ConstantInt(Greater))) &&
PredB == ICmpInst::ICMP_SLT) {
return true;
}
return false;
}
Instruction *InstCombiner::foldICmpSelectConstant(ICmpInst &Cmp,
SelectInst *Select,
ConstantInt *C) {
assert(C && "Cmp RHS should be a constant int!");
// If we're testing a constant value against the result of a three way
// comparison, the result can be expressed directly in terms of the
// original values being compared. Note: We could possibly be more
// aggressive here and remove the hasOneUse test. The original select is
// really likely to simplify or sink when we remove a test of the result.
Value *OrigLHS, *OrigRHS;
ConstantInt *C1LessThan, *C2Equal, *C3GreaterThan;
if (Cmp.hasOneUse() &&
matchThreeWayIntCompare(Select, OrigLHS, OrigRHS, C1LessThan, C2Equal,
C3GreaterThan)) {
assert(C1LessThan && C2Equal && C3GreaterThan);
bool TrueWhenLessThan =
ConstantExpr::getCompare(Cmp.getPredicate(), C1LessThan, C)
->isAllOnesValue();
bool TrueWhenEqual =
ConstantExpr::getCompare(Cmp.getPredicate(), C2Equal, C)
->isAllOnesValue();
bool TrueWhenGreaterThan =
ConstantExpr::getCompare(Cmp.getPredicate(), C3GreaterThan, C)
->isAllOnesValue();
// This generates the new instruction that will replace the original Cmp
// Instruction. Instead of enumerating the various combinations when
// TrueWhenLessThan, TrueWhenEqual and TrueWhenGreaterThan are true versus
// false, we rely on chaining of ORs and future passes of InstCombine to
// simplify the OR further (i.e. a s< b || a == b becomes a s<= b).
// When none of the three constants satisfy the predicate for the RHS (C),
// the entire original Cmp can be simplified to a false.
Value *Cond = Builder.getFalse();
if (TrueWhenLessThan)
Cond = Builder.CreateOr(Cond, Builder.CreateICmp(ICmpInst::ICMP_SLT, OrigLHS, OrigRHS));
if (TrueWhenEqual)
Cond = Builder.CreateOr(Cond, Builder.CreateICmp(ICmpInst::ICMP_EQ, OrigLHS, OrigRHS));
if (TrueWhenGreaterThan)
Cond = Builder.CreateOr(Cond, Builder.CreateICmp(ICmpInst::ICMP_SGT, OrigLHS, OrigRHS));
return replaceInstUsesWith(Cmp, Cond);
}
return nullptr;
}
/// Try to fold integer comparisons with a constant operand: icmp Pred X, C
/// where X is some kind of instruction.
Instruction *InstCombiner::foldICmpInstWithConstant(ICmpInst &Cmp) {
const APInt *C;
if (!match(Cmp.getOperand(1), m_APInt(C)))
return nullptr;
if (auto *BO = dyn_cast<BinaryOperator>(Cmp.getOperand(0))) {
switch (BO->getOpcode()) {
case Instruction::Xor:
if (Instruction *I = foldICmpXorConstant(Cmp, BO, C))
return I;
break;
case Instruction::And:
if (Instruction *I = foldICmpAndConstant(Cmp, BO, C))
return I;
break;
case Instruction::Or:
if (Instruction *I = foldICmpOrConstant(Cmp, BO, C))
return I;
break;
case Instruction::Mul:
if (Instruction *I = foldICmpMulConstant(Cmp, BO, C))
return I;
break;
case Instruction::Shl:
if (Instruction *I = foldICmpShlConstant(Cmp, BO, C))
return I;
break;
case Instruction::LShr:
case Instruction::AShr:
if (Instruction *I = foldICmpShrConstant(Cmp, BO, C))
return I;
break;
case Instruction::UDiv:
if (Instruction *I = foldICmpUDivConstant(Cmp, BO, C))
return I;
LLVM_FALLTHROUGH;
case Instruction::SDiv:
if (Instruction *I = foldICmpDivConstant(Cmp, BO, C))
return I;
break;
case Instruction::Sub:
if (Instruction *I = foldICmpSubConstant(Cmp, BO, C))
return I;
break;
case Instruction::Add:
if (Instruction *I = foldICmpAddConstant(Cmp, BO, C))
return I;
break;
default:
break;
}
// TODO: These folds could be refactored to be part of the above calls.
if (Instruction *I = foldICmpBinOpEqualityWithConstant(Cmp, BO, C))
return I;
}
// Match against CmpInst LHS being instructions other than binary operators.
if (auto *SI = dyn_cast<SelectInst>(Cmp.getOperand(0))) {
// For now, we only support constant integers while folding the
// ICMP(SELECT)) pattern. We can extend this to support vector of integers
// similar to the cases handled by binary ops above.
if (ConstantInt *ConstRHS = dyn_cast<ConstantInt>(Cmp.getOperand(1)))
if (Instruction *I = foldICmpSelectConstant(Cmp, SI, ConstRHS))
return I;
}
if (auto *TI = dyn_cast<TruncInst>(Cmp.getOperand(0))) {
if (Instruction *I = foldICmpTruncConstant(Cmp, TI, C))
return I;
}
if (Instruction *I = foldICmpIntrinsicWithConstant(Cmp, C))
return I;
return nullptr;
}
/// Fold an icmp equality instruction with binary operator LHS and constant RHS:
/// icmp eq/ne BO, C.
Instruction *InstCombiner::foldICmpBinOpEqualityWithConstant(ICmpInst &Cmp,
BinaryOperator *BO,
const APInt *C) {
// TODO: Some of these folds could work with arbitrary constants, but this
// function is limited to scalar and vector splat constants.
if (!Cmp.isEquality())
return nullptr;
ICmpInst::Predicate Pred = Cmp.getPredicate();
bool isICMP_NE = Pred == ICmpInst::ICMP_NE;
Constant *RHS = cast<Constant>(Cmp.getOperand(1));
Value *BOp0 = BO->getOperand(0), *BOp1 = BO->getOperand(1);
switch (BO->getOpcode()) {
case Instruction::SRem:
// If we have a signed (X % (2^c)) == 0, turn it into an unsigned one.
if (C->isNullValue() && BO->hasOneUse()) {
const APInt *BOC;
if (match(BOp1, m_APInt(BOC)) && BOC->sgt(1) && BOC->isPowerOf2()) {
Value *NewRem = Builder.CreateURem(BOp0, BOp1, BO->getName());
return new ICmpInst(Pred, NewRem,
Constant::getNullValue(BO->getType()));
}
}
break;
case Instruction::Add: {
// Replace ((add A, B) != C) with (A != C-B) if B & C are constants.
const APInt *BOC;
if (match(BOp1, m_APInt(BOC))) {
if (BO->hasOneUse()) {
Constant *SubC = ConstantExpr::getSub(RHS, cast<Constant>(BOp1));
return new ICmpInst(Pred, BOp0, SubC);
}
} else if (C->isNullValue()) {
// Replace ((add A, B) != 0) with (A != -B) if A or B is
// efficiently invertible, or if the add has just this one use.
if (Value *NegVal = dyn_castNegVal(BOp1))
return new ICmpInst(Pred, BOp0, NegVal);
if (Value *NegVal = dyn_castNegVal(BOp0))
return new ICmpInst(Pred, NegVal, BOp1);
if (BO->hasOneUse()) {
Value *Neg = Builder.CreateNeg(BOp1);
Neg->takeName(BO);
return new ICmpInst(Pred, BOp0, Neg);
}
}
break;
}
case Instruction::Xor:
if (BO->hasOneUse()) {
if (Constant *BOC = dyn_cast<Constant>(BOp1)) {
// For the xor case, we can xor two constants together, eliminating
// the explicit xor.
return new ICmpInst(Pred, BOp0, ConstantExpr::getXor(RHS, BOC));
} else if (C->isNullValue()) {
// Replace ((xor A, B) != 0) with (A != B)
return new ICmpInst(Pred, BOp0, BOp1);
}
}
break;
case Instruction::Sub:
if (BO->hasOneUse()) {
const APInt *BOC;
if (match(BOp0, m_APInt(BOC))) {
// Replace ((sub BOC, B) != C) with (B != BOC-C).
Constant *SubC = ConstantExpr::getSub(cast<Constant>(BOp0), RHS);
return new ICmpInst(Pred, BOp1, SubC);
} else if (C->isNullValue()) {
// Replace ((sub A, B) != 0) with (A != B).
return new ICmpInst(Pred, BOp0, BOp1);
}
}
break;
case Instruction::Or: {
const APInt *BOC;
if (match(BOp1, m_APInt(BOC)) && BO->hasOneUse() && RHS->isAllOnesValue()) {
// Comparing if all bits outside of a constant mask are set?
// Replace (X | C) == -1 with (X & ~C) == ~C.
// This removes the -1 constant.
Constant *NotBOC = ConstantExpr::getNot(cast<Constant>(BOp1));
Value *And = Builder.CreateAnd(BOp0, NotBOC);
return new ICmpInst(Pred, And, NotBOC);
}
break;
}
case Instruction::And: {
const APInt *BOC;
if (match(BOp1, m_APInt(BOC))) {
// If we have ((X & C) == C), turn it into ((X & C) != 0).
if (C == BOC && C->isPowerOf2())
return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE,
BO, Constant::getNullValue(RHS->getType()));
// Don't perform the following transforms if the AND has multiple uses
if (!BO->hasOneUse())
break;
// Replace (and X, (1 << size(X)-1) != 0) with x s< 0
if (BOC->isSignMask()) {
Constant *Zero = Constant::getNullValue(BOp0->getType());
auto NewPred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
return new ICmpInst(NewPred, BOp0, Zero);
}
// ((X & ~7) == 0) --> X < 8
if (C->isNullValue() && (~(*BOC) + 1).isPowerOf2()) {
Constant *NegBOC = ConstantExpr::getNeg(cast<Constant>(BOp1));
auto NewPred = isICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT;
return new ICmpInst(NewPred, BOp0, NegBOC);
}
}
break;
}
case Instruction::Mul:
if (C->isNullValue() && BO->hasNoSignedWrap()) {
const APInt *BOC;
if (match(BOp1, m_APInt(BOC)) && !BOC->isNullValue()) {
// The trivial case (mul X, 0) is handled by InstSimplify.
// General case : (mul X, C) != 0 iff X != 0
// (mul X, C) == 0 iff X == 0
return new ICmpInst(Pred, BOp0, Constant::getNullValue(RHS->getType()));
}
}
break;
case Instruction::UDiv:
if (C->isNullValue()) {
// (icmp eq/ne (udiv A, B), 0) -> (icmp ugt/ule i32 B, A)
auto NewPred = isICMP_NE ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_UGT;
return new ICmpInst(NewPred, BOp1, BOp0);
}
break;
default:
break;
}
return nullptr;
}
/// Fold an icmp with LLVM intrinsic and constant operand: icmp Pred II, C.
Instruction *InstCombiner::foldICmpIntrinsicWithConstant(ICmpInst &Cmp,
const APInt *C) {
IntrinsicInst *II = dyn_cast<IntrinsicInst>(Cmp.getOperand(0));
if (!II || !Cmp.isEquality())
return nullptr;
// Handle icmp {eq|ne} <intrinsic>, Constant.
Type *Ty = II->getType();
switch (II->getIntrinsicID()) {
case Intrinsic::bswap:
Worklist.Add(II);
Cmp.setOperand(0, II->getArgOperand(0));
Cmp.setOperand(1, ConstantInt::get(Ty, C->byteSwap()));
return &Cmp;
case Intrinsic::ctlz:
case Intrinsic::cttz:
// ctz(A) == bitwidth(A) -> A == 0 and likewise for !=
if (*C == C->getBitWidth()) {
Worklist.Add(II);
Cmp.setOperand(0, II->getArgOperand(0));
Cmp.setOperand(1, ConstantInt::getNullValue(Ty));
return &Cmp;
}
break;
case Intrinsic::ctpop: {
// popcount(A) == 0 -> A == 0 and likewise for !=
// popcount(A) == bitwidth(A) -> A == -1 and likewise for !=
bool IsZero = C->isNullValue();
if (IsZero || *C == C->getBitWidth()) {
Worklist.Add(II);
Cmp.setOperand(0, II->getArgOperand(0));
auto *NewOp =
IsZero ? Constant::getNullValue(Ty) : Constant::getAllOnesValue(Ty);
Cmp.setOperand(1, NewOp);
return &Cmp;
}
break;
}
default:
break;
}
return nullptr;
}
/// Handle icmp with constant (but not simple integer constant) RHS.
Instruction *InstCombiner::foldICmpInstWithConstantNotInt(ICmpInst &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
Constant *RHSC = dyn_cast<Constant>(Op1);
Instruction *LHSI = dyn_cast<Instruction>(Op0);
if (!RHSC || !LHSI)
return nullptr;
switch (LHSI->getOpcode()) {
case Instruction::GetElementPtr:
// icmp pred GEP (P, int 0, int 0, int 0), null -> icmp pred P, null
if (RHSC->isNullValue() &&
cast<GetElementPtrInst>(LHSI)->hasAllZeroIndices())
return new ICmpInst(
I.getPredicate(), LHSI->getOperand(0),
Constant::getNullValue(LHSI->getOperand(0)->getType()));
break;
case Instruction::PHI:
// Only fold icmp into the PHI if the phi and icmp are in the same
// block. If in the same block, we're encouraging jump threading. If
// not, we are just pessimizing the code by making an i1 phi.
if (LHSI->getParent() == I.getParent())
if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
return NV;
break;
case Instruction::Select: {
// If either operand of the select is a constant, we can fold the
// comparison into the select arms, which will cause one to be
// constant folded and the select turned into a bitwise or.
Value *Op1 = nullptr, *Op2 = nullptr;
ConstantInt *CI = nullptr;
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) {
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
CI = dyn_cast<ConstantInt>(Op1);
}
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) {
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
CI = dyn_cast<ConstantInt>(Op2);
}
// We only want to perform this transformation if it will not lead to
// additional code. This is true if either both sides of the select
// fold to a constant (in which case the icmp is replaced with a select
// which will usually simplify) or this is the only user of the
// select (in which case we are trading a select+icmp for a simpler
// select+icmp) or all uses of the select can be replaced based on
// dominance information ("Global cases").
bool Transform = false;
if (Op1 && Op2)
Transform = true;
else if (Op1 || Op2) {
// Local case
if (LHSI->hasOneUse())
Transform = true;
// Global cases
else if (CI && !CI->isZero())
// When Op1 is constant try replacing select with second operand.
// Otherwise Op2 is constant and try replacing select with first
// operand.
Transform =
replacedSelectWithOperand(cast<SelectInst>(LHSI), &I, Op1 ? 2 : 1);
}
if (Transform) {
if (!Op1)
Op1 = Builder.CreateICmp(I.getPredicate(), LHSI->getOperand(1), RHSC,
I.getName());
if (!Op2)
Op2 = Builder.CreateICmp(I.getPredicate(), LHSI->getOperand(2), RHSC,
I.getName());
return SelectInst::Create(LHSI->getOperand(0), Op1, Op2);
}
break;
}
case Instruction::IntToPtr:
// icmp pred inttoptr(X), null -> icmp pred X, 0
if (RHSC->isNullValue() &&
DL.getIntPtrType(RHSC->getType()) == LHSI->getOperand(0)->getType())
return new ICmpInst(
I.getPredicate(), LHSI->getOperand(0),
Constant::getNullValue(LHSI->getOperand(0)->getType()));
break;
case Instruction::Load:
// Try to optimize things like "A[i] > 4" to index computations.
if (GetElementPtrInst *GEP =
dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
!cast<LoadInst>(LHSI)->isVolatile())
if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
return Res;
}
break;
}
return nullptr;
}
/// Try to fold icmp (binop), X or icmp X, (binop).
/// TODO: A large part of this logic is duplicated in InstSimplify's
/// simplifyICmpWithBinOp(). We should be able to share that and avoid the code
/// duplication.
Instruction *InstCombiner::foldICmpBinOp(ICmpInst &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// Special logic for binary operators.
BinaryOperator *BO0 = dyn_cast<BinaryOperator>(Op0);
BinaryOperator *BO1 = dyn_cast<BinaryOperator>(Op1);
if (!BO0 && !BO1)
return nullptr;
const CmpInst::Predicate Pred = I.getPredicate();
bool NoOp0WrapProblem = false, NoOp1WrapProblem = false;
if (BO0 && isa<OverflowingBinaryOperator>(BO0))
NoOp0WrapProblem =
ICmpInst::isEquality(Pred) ||
(CmpInst::isUnsigned(Pred) && BO0->hasNoUnsignedWrap()) ||
(CmpInst::isSigned(Pred) && BO0->hasNoSignedWrap());
if (BO1 && isa<OverflowingBinaryOperator>(BO1))
NoOp1WrapProblem =
ICmpInst::isEquality(Pred) ||
(CmpInst::isUnsigned(Pred) && BO1->hasNoUnsignedWrap()) ||
(CmpInst::isSigned(Pred) && BO1->hasNoSignedWrap());
// Analyze the case when either Op0 or Op1 is an add instruction.
// Op0 = A + B (or A and B are null); Op1 = C + D (or C and D are null).
Value *A = nullptr, *B = nullptr, *C = nullptr, *D = nullptr;
if (BO0 && BO0->getOpcode() == Instruction::Add) {
A = BO0->getOperand(0);
B = BO0->getOperand(1);
}
if (BO1 && BO1->getOpcode() == Instruction::Add) {
C = BO1->getOperand(0);
D = BO1->getOperand(1);
}
// icmp (X+Y), X -> icmp Y, 0 for equalities or if there is no overflow.
if ((A == Op1 || B == Op1) && NoOp0WrapProblem)
return new ICmpInst(Pred, A == Op1 ? B : A,
Constant::getNullValue(Op1->getType()));
// icmp X, (X+Y) -> icmp 0, Y for equalities or if there is no overflow.
if ((C == Op0 || D == Op0) && NoOp1WrapProblem)
return new ICmpInst(Pred, Constant::getNullValue(Op0->getType()),
C == Op0 ? D : C);
// icmp (X+Y), (X+Z) -> icmp Y, Z for equalities or if there is no overflow.
if (A && C && (A == C || A == D || B == C || B == D) && NoOp0WrapProblem &&
NoOp1WrapProblem &&
// Try not to increase register pressure.
BO0->hasOneUse() && BO1->hasOneUse()) {
// Determine Y and Z in the form icmp (X+Y), (X+Z).
Value *Y, *Z;
if (A == C) {
// C + B == C + D -> B == D
Y = B;
Z = D;
} else if (A == D) {
// D + B == C + D -> B == C
Y = B;
Z = C;
} else if (B == C) {
// A + C == C + D -> A == D
Y = A;
Z = D;
} else {
assert(B == D);
// A + D == C + D -> A == C
Y = A;
Z = C;
}
return new ICmpInst(Pred, Y, Z);
}
// icmp slt (X + -1), Y -> icmp sle X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLT &&
match(B, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SLE, A, Op1);
// icmp sge (X + -1), Y -> icmp sgt X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGE &&
match(B, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SGT, A, Op1);
// icmp sle (X + 1), Y -> icmp slt X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLE && match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_SLT, A, Op1);
// icmp sgt (X + 1), Y -> icmp sge X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGT && match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_SGE, A, Op1);
// icmp sgt X, (Y + -1) -> icmp sge X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGT &&
match(D, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SGE, Op0, C);
// icmp sle X, (Y + -1) -> icmp slt X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLE &&
match(D, m_AllOnes()))
return new ICmpInst(CmpInst::ICMP_SLT, Op0, C);
// icmp sge X, (Y + 1) -> icmp sgt X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGE && match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_SGT, Op0, C);
// icmp slt X, (Y + 1) -> icmp sle X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLT && match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_SLE, Op0, C);
// TODO: The subtraction-related identities shown below also hold, but
// canonicalization from (X -nuw 1) to (X + -1) means that the combinations
// wouldn't happen even if they were implemented.
//
// icmp ult (X - 1), Y -> icmp ule X, Y
// icmp uge (X - 1), Y -> icmp ugt X, Y
// icmp ugt X, (Y - 1) -> icmp uge X, Y
// icmp ule X, (Y - 1) -> icmp ult X, Y
// icmp ule (X + 1), Y -> icmp ult X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_ULE && match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_ULT, A, Op1);
// icmp ugt (X + 1), Y -> icmp uge X, Y
if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_UGT && match(B, m_One()))
return new ICmpInst(CmpInst::ICMP_UGE, A, Op1);
// icmp uge X, (Y + 1) -> icmp ugt X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_UGE && match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_UGT, Op0, C);
// icmp ult X, (Y + 1) -> icmp ule X, Y
if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_ULT && match(D, m_One()))
return new ICmpInst(CmpInst::ICMP_ULE, Op0, C);
// if C1 has greater magnitude than C2:
// icmp (X + C1), (Y + C2) -> icmp (X + C3), Y
// s.t. C3 = C1 - C2
//
// if C2 has greater magnitude than C1:
// icmp (X + C1), (Y + C2) -> icmp X, (Y + C3)
// s.t. C3 = C2 - C1
if (A && C && NoOp0WrapProblem && NoOp1WrapProblem &&
(BO0->hasOneUse() || BO1->hasOneUse()) && !I.isUnsigned())
if (ConstantInt *C1 = dyn_cast<ConstantInt>(B))
if (ConstantInt *C2 = dyn_cast<ConstantInt>(D)) {
const APInt &AP1 = C1->getValue();
const APInt &AP2 = C2->getValue();
if (AP1.isNegative() == AP2.isNegative()) {
APInt AP1Abs = C1->getValue().abs();
APInt AP2Abs = C2->getValue().abs();
if (AP1Abs.uge(AP2Abs)) {
ConstantInt *C3 = Builder.getInt(AP1 - AP2);
Value *NewAdd = Builder.CreateNSWAdd(A, C3);
return new ICmpInst(Pred, NewAdd, C);
} else {
ConstantInt *C3 = Builder.getInt(AP2 - AP1);
Value *NewAdd = Builder.CreateNSWAdd(C, C3);
return new ICmpInst(Pred, A, NewAdd);
}
}
}
// Analyze the case when either Op0 or Op1 is a sub instruction.
// Op0 = A - B (or A and B are null); Op1 = C - D (or C and D are null).
A = nullptr;
B = nullptr;
C = nullptr;
D = nullptr;
if (BO0 && BO0->getOpcode() == Instruction::Sub) {
A = BO0->getOperand(0);
B = BO0->getOperand(1);
}
if (BO1 && BO1->getOpcode() == Instruction::Sub) {
C = BO1->getOperand(0);
D = BO1->getOperand(1);
}
// icmp (X-Y), X -> icmp 0, Y for equalities or if there is no overflow.
if (A == Op1 && NoOp0WrapProblem)
return new ICmpInst(Pred, Constant::getNullValue(Op1->getType()), B);
// icmp X, (X-Y) -> icmp Y, 0 for equalities or if there is no overflow.
if (C == Op0 && NoOp1WrapProblem)
return new ICmpInst(Pred, D, Constant::getNullValue(Op0->getType()));
// icmp (Y-X), (Z-X) -> icmp Y, Z for equalities or if there is no overflow.
if (B && D && B == D && NoOp0WrapProblem && NoOp1WrapProblem &&
// Try not to increase register pressure.
BO0->hasOneUse() && BO1->hasOneUse())
return new ICmpInst(Pred, A, C);
// icmp (X-Y), (X-Z) -> icmp Z, Y for equalities or if there is no overflow.
if (A && C && A == C && NoOp0WrapProblem && NoOp1WrapProblem &&
// Try not to increase register pressure.
BO0->hasOneUse() && BO1->hasOneUse())
return new ICmpInst(Pred, D, B);
// icmp (0-X) < cst --> x > -cst
if (NoOp0WrapProblem && ICmpInst::isSigned(Pred)) {
Value *X;
if (match(BO0, m_Neg(m_Value(X))))
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))
if (!RHSC->isMinValue(/*isSigned=*/true))
return new ICmpInst(I.getSwappedPredicate(), X,
ConstantExpr::getNeg(RHSC));
}
BinaryOperator *SRem = nullptr;
// icmp (srem X, Y), Y
if (BO0 && BO0->getOpcode() == Instruction::SRem && Op1 == BO0->getOperand(1))
SRem = BO0;
// icmp Y, (srem X, Y)
else if (BO1 && BO1->getOpcode() == Instruction::SRem &&
Op0 == BO1->getOperand(1))
SRem = BO1;
if (SRem) {
// We don't check hasOneUse to avoid increasing register pressure because
// the value we use is the same value this instruction was already using.
switch (SRem == BO0 ? ICmpInst::getSwappedPredicate(Pred) : Pred) {
default:
break;
case ICmpInst::ICMP_EQ:
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
case ICmpInst::ICMP_NE:
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE:
return new ICmpInst(ICmpInst::ICMP_SGT, SRem->getOperand(1),
Constant::getAllOnesValue(SRem->getType()));
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE:
return new ICmpInst(ICmpInst::ICMP_SLT, SRem->getOperand(1),
Constant::getNullValue(SRem->getType()));
}
}
if (BO0 && BO1 && BO0->getOpcode() == BO1->getOpcode() && BO0->hasOneUse() &&
BO1->hasOneUse() && BO0->getOperand(1) == BO1->getOperand(1)) {
switch (BO0->getOpcode()) {
default:
break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Xor: {
if (I.isEquality()) // a+x icmp eq/ne b+x --> a icmp b
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
const APInt *C;
if (match(BO0->getOperand(1), m_APInt(C))) {
// icmp u/s (a ^ signmask), (b ^ signmask) --> icmp s/u a, b
if (C->isSignMask()) {
ICmpInst::Predicate NewPred =
I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
return new ICmpInst(NewPred, BO0->getOperand(0), BO1->getOperand(0));
}
// icmp u/s (a ^ maxsignval), (b ^ maxsignval) --> icmp s/u' a, b
if (BO0->getOpcode() == Instruction::Xor && C->isMaxSignedValue()) {
ICmpInst::Predicate NewPred =
I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
NewPred = I.getSwappedPredicate(NewPred);
return new ICmpInst(NewPred, BO0->getOperand(0), BO1->getOperand(0));
}
}
break;
}
case Instruction::Mul: {
if (!I.isEquality())
break;
const APInt *C;
if (match(BO0->getOperand(1), m_APInt(C)) && !C->isNullValue() &&
!C->isOneValue()) {
// icmp eq/ne (X * C), (Y * C) --> icmp (X & Mask), (Y & Mask)
// Mask = -1 >> count-trailing-zeros(C).
if (unsigned TZs = C->countTrailingZeros()) {
Constant *Mask = ConstantInt::get(
BO0->getType(),
APInt::getLowBitsSet(C->getBitWidth(), C->getBitWidth() - TZs));
Value *And1 = Builder.CreateAnd(BO0->getOperand(0), Mask);
Value *And2 = Builder.CreateAnd(BO1->getOperand(0), Mask);
return new ICmpInst(Pred, And1, And2);
}
// If there are no trailing zeros in the multiplier, just eliminate
// the multiplies (no masking is needed):
// icmp eq/ne (X * C), (Y * C) --> icmp eq/ne X, Y
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
}
break;
}
case Instruction::UDiv:
case Instruction::LShr:
if (I.isSigned() || !BO0->isExact() || !BO1->isExact())
break;
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
case Instruction::SDiv:
if (!I.isEquality() || !BO0->isExact() || !BO1->isExact())
break;
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
case Instruction::AShr:
if (!BO0->isExact() || !BO1->isExact())
break;
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
case Instruction::Shl: {
bool NUW = BO0->hasNoUnsignedWrap() && BO1->hasNoUnsignedWrap();
bool NSW = BO0->hasNoSignedWrap() && BO1->hasNoSignedWrap();
if (!NUW && !NSW)
break;
if (!NSW && I.isSigned())
break;
return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
}
}
}
if (BO0) {
// Transform A & (L - 1) `ult` L --> L != 0
auto LSubOne = m_Add(m_Specific(Op1), m_AllOnes());
auto BitwiseAnd = m_c_And(m_Value(), LSubOne);
if (match(BO0, BitwiseAnd) && Pred == ICmpInst::ICMP_ULT) {
auto *Zero = Constant::getNullValue(BO0->getType());
return new ICmpInst(ICmpInst::ICMP_NE, Op1, Zero);
}
}
return nullptr;
}
/// Fold icmp Pred min|max(X, Y), X.
static Instruction *foldICmpWithMinMax(ICmpInst &Cmp) {
ICmpInst::Predicate Pred = Cmp.getPredicate();
Value *Op0 = Cmp.getOperand(0);
Value *X = Cmp.getOperand(1);
// Canonicalize minimum or maximum operand to LHS of the icmp.
if (match(X, m_c_SMin(m_Specific(Op0), m_Value())) ||
match(X, m_c_SMax(m_Specific(Op0), m_Value())) ||
match(X, m_c_UMin(m_Specific(Op0), m_Value())) ||
match(X, m_c_UMax(m_Specific(Op0), m_Value()))) {
std::swap(Op0, X);
Pred = Cmp.getSwappedPredicate();
}
Value *Y;
if (match(Op0, m_c_SMin(m_Specific(X), m_Value(Y)))) {
// smin(X, Y) == X --> X s<= Y
// smin(X, Y) s>= X --> X s<= Y
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_SGE)
return new ICmpInst(ICmpInst::ICMP_SLE, X, Y);
// smin(X, Y) != X --> X s> Y
// smin(X, Y) s< X --> X s> Y
if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_SLT)
return new ICmpInst(ICmpInst::ICMP_SGT, X, Y);
// These cases should be handled in InstSimplify:
// smin(X, Y) s<= X --> true
// smin(X, Y) s> X --> false
return nullptr;
}
if (match(Op0, m_c_SMax(m_Specific(X), m_Value(Y)))) {
// smax(X, Y) == X --> X s>= Y
// smax(X, Y) s<= X --> X s>= Y
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_SGE, X, Y);
// smax(X, Y) != X --> X s< Y
// smax(X, Y) s> X --> X s< Y
if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_SGT)
return new ICmpInst(ICmpInst::ICMP_SLT, X, Y);
// These cases should be handled in InstSimplify:
// smax(X, Y) s>= X --> true
// smax(X, Y) s< X --> false
return nullptr;
}
if (match(Op0, m_c_UMin(m_Specific(X), m_Value(Y)))) {
// umin(X, Y) == X --> X u<= Y
// umin(X, Y) u>= X --> X u<= Y
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_UGE)
return new ICmpInst(ICmpInst::ICMP_ULE, X, Y);
// umin(X, Y) != X --> X u> Y
// umin(X, Y) u< X --> X u> Y
if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_ULT)
return new ICmpInst(ICmpInst::ICMP_UGT, X, Y);
// These cases should be handled in InstSimplify:
// umin(X, Y) u<= X --> true
// umin(X, Y) u> X --> false
return nullptr;
}
if (match(Op0, m_c_UMax(m_Specific(X), m_Value(Y)))) {
// umax(X, Y) == X --> X u>= Y
// umax(X, Y) u<= X --> X u>= Y
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_ULE)
return new ICmpInst(ICmpInst::ICMP_UGE, X, Y);
// umax(X, Y) != X --> X u< Y
// umax(X, Y) u> X --> X u< Y
if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_UGT)
return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
// These cases should be handled in InstSimplify:
// umax(X, Y) u>= X --> true
// umax(X, Y) u< X --> false
return nullptr;
}
return nullptr;
}
Instruction *InstCombiner::foldICmpEquality(ICmpInst &I) {
if (!I.isEquality())
return nullptr;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
const CmpInst::Predicate Pred = I.getPredicate();
Value *A, *B, *C, *D;
if (match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
if (A == Op1 || B == Op1) { // (A^B) == A -> B == 0
Value *OtherVal = A == Op1 ? B : A;
return new ICmpInst(Pred, OtherVal, Constant::getNullValue(A->getType()));
}
if (match(Op1, m_Xor(m_Value(C), m_Value(D)))) {
// A^c1 == C^c2 --> A == C^(c1^c2)
ConstantInt *C1, *C2;
if (match(B, m_ConstantInt(C1)) && match(D, m_ConstantInt(C2)) &&
Op1->hasOneUse()) {
Constant *NC = Builder.getInt(C1->getValue() ^ C2->getValue());
Value *Xor = Builder.CreateXor(C, NC);
return new ICmpInst(Pred, A, Xor);
}
// A^B == A^D -> B == D
if (A == C)
return new ICmpInst(Pred, B, D);
if (A == D)
return new ICmpInst(Pred, B, C);
if (B == C)
return new ICmpInst(Pred, A, D);
if (B == D)
return new ICmpInst(Pred, A, C);
}
}
if (match(Op1, m_Xor(m_Value(A), m_Value(B))) && (A == Op0 || B == Op0)) {
// A == (A^B) -> B == 0
Value *OtherVal = A == Op0 ? B : A;
return new ICmpInst(Pred, OtherVal, Constant::getNullValue(A->getType()));
}
// (X&Z) == (Y&Z) -> (X^Y) & Z == 0
if (match(Op0, m_OneUse(m_And(m_Value(A), m_Value(B)))) &&
match(Op1, m_OneUse(m_And(m_Value(C), m_Value(D))))) {
Value *X = nullptr, *Y = nullptr, *Z = nullptr;
if (A == C) {
X = B;
Y = D;
Z = A;
} else if (A == D) {
X = B;
Y = C;
Z = A;
} else if (B == C) {
X = A;
Y = D;
Z = B;
} else if (B == D) {
X = A;
Y = C;
Z = B;
}
if (X) { // Build (X^Y) & Z
Op1 = Builder.CreateXor(X, Y);
Op1 = Builder.CreateAnd(Op1, Z);
I.setOperand(0, Op1);
I.setOperand(1, Constant::getNullValue(Op1->getType()));
return &I;
}
}
// Transform (zext A) == (B & (1<<X)-1) --> A == (trunc B)
// and (B & (1<<X)-1) == (zext A) --> A == (trunc B)
ConstantInt *Cst1;
if ((Op0->hasOneUse() && match(Op0, m_ZExt(m_Value(A))) &&
match(Op1, m_And(m_Value(B), m_ConstantInt(Cst1)))) ||
(Op1->hasOneUse() && match(Op0, m_And(m_Value(B), m_ConstantInt(Cst1))) &&
match(Op1, m_ZExt(m_Value(A))))) {
APInt Pow2 = Cst1->getValue() + 1;
if (Pow2.isPowerOf2() && isa<IntegerType>(A->getType()) &&
Pow2.logBase2() == cast<IntegerType>(A->getType())->getBitWidth())
return new ICmpInst(Pred, A, Builder.CreateTrunc(B, A->getType()));
}
// (A >> C) == (B >> C) --> (A^B) u< (1 << C)
// For lshr and ashr pairs.
if ((match(Op0, m_OneUse(m_LShr(m_Value(A), m_ConstantInt(Cst1)))) &&
match(Op1, m_OneUse(m_LShr(m_Value(B), m_Specific(Cst1))))) ||
(match(Op0, m_OneUse(m_AShr(m_Value(A), m_ConstantInt(Cst1)))) &&
match(Op1, m_OneUse(m_AShr(m_Value(B), m_Specific(Cst1)))))) {
unsigned TypeBits = Cst1->getBitWidth();
unsigned ShAmt = (unsigned)Cst1->getLimitedValue(TypeBits);
if (ShAmt < TypeBits && ShAmt != 0) {
ICmpInst::Predicate NewPred =
Pred == ICmpInst::ICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT;
Value *Xor = Builder.CreateXor(A, B, I.getName() + ".unshifted");
APInt CmpVal = APInt::getOneBitSet(TypeBits, ShAmt);
return new ICmpInst(NewPred, Xor, Builder.getInt(CmpVal));
}
}
// (A << C) == (B << C) --> ((A^B) & (~0U >> C)) == 0
if (match(Op0, m_OneUse(m_Shl(m_Value(A), m_ConstantInt(Cst1)))) &&
match(Op1, m_OneUse(m_Shl(m_Value(B), m_Specific(Cst1))))) {
unsigned TypeBits = Cst1->getBitWidth();
unsigned ShAmt = (unsigned)Cst1->getLimitedValue(TypeBits);
if (ShAmt < TypeBits && ShAmt != 0) {
Value *Xor = Builder.CreateXor(A, B, I.getName() + ".unshifted");
APInt AndVal = APInt::getLowBitsSet(TypeBits, TypeBits - ShAmt);
Value *And = Builder.CreateAnd(Xor, Builder.getInt(AndVal),
I.getName() + ".mask");
return new ICmpInst(Pred, And, Constant::getNullValue(Cst1->getType()));
}
}
// Transform "icmp eq (trunc (lshr(X, cst1)), cst" to
// "icmp (and X, mask), cst"
uint64_t ShAmt = 0;
if (Op0->hasOneUse() &&
match(Op0, m_Trunc(m_OneUse(m_LShr(m_Value(A), m_ConstantInt(ShAmt))))) &&
match(Op1, m_ConstantInt(Cst1)) &&
// Only do this when A has multiple uses. This is most important to do
// when it exposes other optimizations.
!A->hasOneUse()) {
unsigned ASize = cast<IntegerType>(A->getType())->getPrimitiveSizeInBits();
if (ShAmt < ASize) {
APInt MaskV =
APInt::getLowBitsSet(ASize, Op0->getType()->getPrimitiveSizeInBits());
MaskV <<= ShAmt;
APInt CmpV = Cst1->getValue().zext(ASize);
CmpV <<= ShAmt;
Value *Mask = Builder.CreateAnd(A, Builder.getInt(MaskV));
return new ICmpInst(Pred, Mask, Builder.getInt(CmpV));
}
}
// If both operands are byte-swapped or bit-reversed, just compare the
// original values.
// TODO: Move this to a function similar to foldICmpIntrinsicWithConstant()
// and handle more intrinsics.
if ((match(Op0, m_BSwap(m_Value(A))) && match(Op1, m_BSwap(m_Value(B)))) ||
(match(Op0, m_BitReverse(m_Value(A))) &&
match(Op1, m_BitReverse(m_Value(B)))))
return new ICmpInst(Pred, A, B);
return nullptr;
}
/// Handle icmp (cast x to y), (cast/cst). We only handle extending casts so
/// far.
Instruction *InstCombiner::foldICmpWithCastAndCast(ICmpInst &ICmp) {
const CastInst *LHSCI = cast<CastInst>(ICmp.getOperand(0));
Value *LHSCIOp = LHSCI->getOperand(0);
Type *SrcTy = LHSCIOp->getType();
Type *DestTy = LHSCI->getType();
Value *RHSCIOp;
// Turn icmp (ptrtoint x), (ptrtoint/c) into a compare of the input if the
// integer type is the same size as the pointer type.
if (LHSCI->getOpcode() == Instruction::PtrToInt &&
DL.getPointerTypeSizeInBits(SrcTy) == DestTy->getIntegerBitWidth()) {
Value *RHSOp = nullptr;
if (auto *RHSC = dyn_cast<PtrToIntOperator>(ICmp.getOperand(1))) {
Value *RHSCIOp = RHSC->getOperand(0);
if (RHSCIOp->getType()->getPointerAddressSpace() ==
LHSCIOp->getType()->getPointerAddressSpace()) {
RHSOp = RHSC->getOperand(0);
// If the pointer types don't match, insert a bitcast.
if (LHSCIOp->getType() != RHSOp->getType())
RHSOp = Builder.CreateBitCast(RHSOp, LHSCIOp->getType());
}
} else if (auto *RHSC = dyn_cast<Constant>(ICmp.getOperand(1))) {
RHSOp = ConstantExpr::getIntToPtr(RHSC, SrcTy);
}
if (RHSOp)
return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSOp);
}
// The code below only handles extension cast instructions, so far.
// Enforce this.
if (LHSCI->getOpcode() != Instruction::ZExt &&
LHSCI->getOpcode() != Instruction::SExt)
return nullptr;
bool isSignedExt = LHSCI->getOpcode() == Instruction::SExt;
bool isSignedCmp = ICmp.isSigned();
if (auto *CI = dyn_cast<CastInst>(ICmp.getOperand(1))) {
// Not an extension from the same type?
RHSCIOp = CI->getOperand(0);
if (RHSCIOp->getType() != LHSCIOp->getType())
return nullptr;
// If the signedness of the two casts doesn't agree (i.e. one is a sext
// and the other is a zext), then we can't handle this.
if (CI->getOpcode() != LHSCI->getOpcode())
return nullptr;
// Deal with equality cases early.
if (ICmp.isEquality())
return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSCIOp);
// A signed comparison of sign extended values simplifies into a
// signed comparison.
if (isSignedCmp && isSignedExt)
return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSCIOp);
// The other three cases all fold into an unsigned comparison.
return new ICmpInst(ICmp.getUnsignedPredicate(), LHSCIOp, RHSCIOp);
}
// If we aren't dealing with a constant on the RHS, exit early.
auto *C = dyn_cast<Constant>(ICmp.getOperand(1));
if (!C)
return nullptr;
// Compute the constant that would happen if we truncated to SrcTy then
// re-extended to DestTy.
Constant *Res1 = ConstantExpr::getTrunc(C, SrcTy);
Constant *Res2 = ConstantExpr::getCast(LHSCI->getOpcode(), Res1, DestTy);
// If the re-extended constant didn't change...
if (Res2 == C) {
// Deal with equality cases early.
if (ICmp.isEquality())
return new ICmpInst(ICmp.getPredicate(), LHSCIOp, Res1);
// A signed comparison of sign extended values simplifies into a
// signed comparison.
if (isSignedExt && isSignedCmp)
return new ICmpInst(ICmp.getPredicate(), LHSCIOp, Res1);
// The other three cases all fold into an unsigned comparison.
return new ICmpInst(ICmp.getUnsignedPredicate(), LHSCIOp, Res1);
}
// The re-extended constant changed, partly changed (in the case of a vector),
// or could not be determined to be equal (in the case of a constant
// expression), so the constant cannot be represented in the shorter type.
// Consequently, we cannot emit a simple comparison.
// All the cases that fold to true or false will have already been handled
// by SimplifyICmpInst, so only deal with the tricky case.
if (isSignedCmp || !isSignedExt || !isa<ConstantInt>(C))
return nullptr;
// Evaluate the comparison for LT (we invert for GT below). LE and GE cases
// should have been folded away previously and not enter in here.
// We're performing an unsigned comp with a sign extended value.
// This is true if the input is >= 0. [aka >s -1]
Constant *NegOne = Constant::getAllOnesValue(SrcTy);
Value *Result = Builder.CreateICmpSGT(LHSCIOp, NegOne, ICmp.getName());
// Finally, return the value computed.
if (ICmp.getPredicate() == ICmpInst::ICMP_ULT)
return replaceInstUsesWith(ICmp, Result);
assert(ICmp.getPredicate() == ICmpInst::ICMP_UGT && "ICmp should be folded!");
return BinaryOperator::CreateNot(Result);
}
bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
Value *RHS, Instruction &OrigI,
Value *&Result, Constant *&Overflow) {
if (OrigI.isCommutative() && isa<Constant>(LHS) && !isa<Constant>(RHS))
std::swap(LHS, RHS);
auto SetResult = [&](Value *OpResult, Constant *OverflowVal, bool ReuseName) {
Result = OpResult;
Overflow = OverflowVal;
if (ReuseName)
Result->takeName(&OrigI);
return true;
};
// If the overflow check was an add followed by a compare, the insertion point
// may be pointing to the compare. We want to insert the new instructions
// before the add in case there are uses of the add between the add and the
// compare.
Builder.SetInsertPoint(&OrigI);
switch (OCF) {
case OCF_INVALID:
llvm_unreachable("bad overflow check kind!");
case OCF_UNSIGNED_ADD: {
OverflowResult OR = computeOverflowForUnsignedAdd(LHS, RHS, &OrigI);
if (OR == OverflowResult::NeverOverflows)
return SetResult(Builder.CreateNUWAdd(LHS, RHS), Builder.getFalse(),
true);
if (OR == OverflowResult::AlwaysOverflows)
return SetResult(Builder.CreateAdd(LHS, RHS), Builder.getTrue(), true);
// Fall through uadd into sadd
LLVM_FALLTHROUGH;
}
case OCF_SIGNED_ADD: {
// X + 0 -> {X, false}
if (match(RHS, m_Zero()))
return SetResult(LHS, Builder.getFalse(), false);
// We can strength reduce this signed add into a regular add if we can prove
// that it will never overflow.
if (OCF == OCF_SIGNED_ADD)
if (willNotOverflowSignedAdd(LHS, RHS, OrigI))
return SetResult(Builder.CreateNSWAdd(LHS, RHS), Builder.getFalse(),
true);
break;
}
case OCF_UNSIGNED_SUB:
case OCF_SIGNED_SUB: {
// X - 0 -> {X, false}
if (match(RHS, m_Zero()))
return SetResult(LHS, Builder.getFalse(), false);
if (OCF == OCF_SIGNED_SUB) {
if (willNotOverflowSignedSub(LHS, RHS, OrigI))
return SetResult(Builder.CreateNSWSub(LHS, RHS), Builder.getFalse(),
true);
} else {
if (willNotOverflowUnsignedSub(LHS, RHS, OrigI))
return SetResult(Builder.CreateNUWSub(LHS, RHS), Builder.getFalse(),
true);
}
break;
}
case OCF_UNSIGNED_MUL: {
OverflowResult OR = computeOverflowForUnsignedMul(LHS, RHS, &OrigI);
if (OR == OverflowResult::NeverOverflows)
return SetResult(Builder.CreateNUWMul(LHS, RHS), Builder.getFalse(),
true);
if (OR == OverflowResult::AlwaysOverflows)
return SetResult(Builder.CreateMul(LHS, RHS), Builder.getTrue(), true);
LLVM_FALLTHROUGH;
}
case OCF_SIGNED_MUL:
// X * undef -> undef
if (isa<UndefValue>(RHS))
return SetResult(RHS, UndefValue::get(Builder.getInt1Ty()), false);
// X * 0 -> {0, false}
if (match(RHS, m_Zero()))
return SetResult(RHS, Builder.getFalse(), false);
// X * 1 -> {X, false}
if (match(RHS, m_One()))
return SetResult(LHS, Builder.getFalse(), false);
if (OCF == OCF_SIGNED_MUL)
if (willNotOverflowSignedMul(LHS, RHS, OrigI))
return SetResult(Builder.CreateNSWMul(LHS, RHS), Builder.getFalse(),
true);
break;
}
return false;
}
/// \brief Recognize and process idiom involving test for multiplication
/// overflow.
///
/// The caller has matched a pattern of the form:
/// I = cmp u (mul(zext A, zext B), V
/// The function checks if this is a test for overflow and if so replaces
/// multiplication with call to 'mul.with.overflow' intrinsic.
///
/// \param I Compare instruction.
/// \param MulVal Result of 'mult' instruction. It is one of the arguments of
/// the compare instruction. Must be of integer type.
/// \param OtherVal The other argument of compare instruction.
/// \returns Instruction which must replace the compare instruction, NULL if no
/// replacement required.
static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
Value *OtherVal, InstCombiner &IC) {
// Don't bother doing this transformation for pointers, don't do it for
// vectors.
if (!isa<IntegerType>(MulVal->getType()))
return nullptr;
assert(I.getOperand(0) == MulVal || I.getOperand(1) == MulVal);
assert(I.getOperand(0) == OtherVal || I.getOperand(1) == OtherVal);
auto *MulInstr = dyn_cast<Instruction>(MulVal);
if (!MulInstr)
return nullptr;
assert(MulInstr->getOpcode() == Instruction::Mul);
auto *LHS = cast<ZExtOperator>(MulInstr->getOperand(0)),
*RHS = cast<ZExtOperator>(MulInstr->getOperand(1));
assert(LHS->getOpcode() == Instruction::ZExt);
assert(RHS->getOpcode() == Instruction::ZExt);
Value *A = LHS->getOperand(0), *B = RHS->getOperand(0);
// Calculate type and width of the result produced by mul.with.overflow.
Type *TyA = A->getType(), *TyB = B->getType();
unsigned WidthA = TyA->getPrimitiveSizeInBits(),
WidthB = TyB->getPrimitiveSizeInBits();
unsigned MulWidth;
Type *MulType;
if (WidthB > WidthA) {
MulWidth = WidthB;
MulType = TyB;
} else {
MulWidth = WidthA;
MulType = TyA;
}
// In order to replace the original mul with a narrower mul.with.overflow,
// all uses must ignore upper bits of the product. The number of used low
// bits must be not greater than the width of mul.with.overflow.
if (MulVal->hasNUsesOrMore(2))
for (User *U : MulVal->users()) {
if (U == &I)
continue;
if (TruncInst *TI = dyn_cast<TruncInst>(U)) {
// Check if truncation ignores bits above MulWidth.
unsigned TruncWidth = TI->getType()->getPrimitiveSizeInBits();
if (TruncWidth > MulWidth)
return nullptr;
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U)) {
// Check if AND ignores bits above MulWidth.
if (BO->getOpcode() != Instruction::And)
return nullptr;
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
const APInt &CVal = CI->getValue();
if (CVal.getBitWidth() - CVal.countLeadingZeros() > MulWidth)
return nullptr;
} else {
// In this case we could have the operand of the binary operation
// being defined in another block, and performing the replacement
// could break the dominance relation.
return nullptr;
}
} else {
// Other uses prohibit this transformation.
return nullptr;
}
}
// Recognize patterns
switch (I.getPredicate()) {
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp eq/neq mulval, zext trunc mulval
if (ZExtInst *Zext = dyn_cast<ZExtInst>(OtherVal))
if (Zext->hasOneUse()) {
Value *ZextArg = Zext->getOperand(0);
if (TruncInst *Trunc = dyn_cast<TruncInst>(ZextArg))
if (Trunc->getType()->getPrimitiveSizeInBits() == MulWidth)
break; //Recognized
}
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp eq/neq mulval, and(mulval, mask), mask selects low MulWidth bits.
ConstantInt *CI;
Value *ValToMask;
if (match(OtherVal, m_And(m_Value(ValToMask), m_ConstantInt(CI)))) {
if (ValToMask != MulVal)
return nullptr;
const APInt &CVal = CI->getValue() + 1;
if (CVal.isPowerOf2()) {
unsigned MaskWidth = CVal.logBase2();
if (MaskWidth == MulWidth)
break; // Recognized
}
}
return nullptr;
case ICmpInst::ICMP_UGT:
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp ugt mulval, max
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
APInt MaxVal = APInt::getMaxValue(MulWidth);
MaxVal = MaxVal.zext(CI->getBitWidth());
if (MaxVal.eq(CI->getValue()))
break; // Recognized
}
return nullptr;
case ICmpInst::ICMP_UGE:
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp uge mulval, max+1
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
APInt MaxVal = APInt::getOneBitSet(CI->getBitWidth(), MulWidth);
if (MaxVal.eq(CI->getValue()))
break; // Recognized
}
return nullptr;
case ICmpInst::ICMP_ULE:
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp ule mulval, max
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
APInt MaxVal = APInt::getMaxValue(MulWidth);
MaxVal = MaxVal.zext(CI->getBitWidth());
if (MaxVal.eq(CI->getValue()))
break; // Recognized
}
return nullptr;
case ICmpInst::ICMP_ULT:
// Recognize pattern:
// mulval = mul(zext A, zext B)
// cmp ule mulval, max + 1
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
APInt MaxVal = APInt::getOneBitSet(CI->getBitWidth(), MulWidth);
if (MaxVal.eq(CI->getValue()))
break; // Recognized
}
return nullptr;
default:
return nullptr;
}
InstCombiner::BuilderTy &Builder = IC.Builder;
Builder.SetInsertPoint(MulInstr);
// Replace: mul(zext A, zext B) --> mul.with.overflow(A, B)
Value *MulA = A, *MulB = B;
if (WidthA < MulWidth)
MulA = Builder.CreateZExt(A, MulType);
if (WidthB < MulWidth)
MulB = Builder.CreateZExt(B, MulType);
Value *F = Intrinsic::getDeclaration(I.getModule(),
Intrinsic::umul_with_overflow, MulType);
CallInst *Call = Builder.CreateCall(F, {MulA, MulB}, "umul");
IC.Worklist.Add(MulInstr);
// If there are uses of mul result other than the comparison, we know that
// they are truncation or binary AND. Change them to use result of
// mul.with.overflow and adjust properly mask/size.
if (MulVal->hasNUsesOrMore(2)) {
Value *Mul = Builder.CreateExtractValue(Call, 0, "umul.value");
for (User *U : MulVal->users()) {
if (U == &I || U == OtherVal)
continue;
if (TruncInst *TI = dyn_cast<TruncInst>(U)) {
if (TI->getType()->getPrimitiveSizeInBits() == MulWidth)
IC.replaceInstUsesWith(*TI, Mul);
else
TI->setOperand(0, Mul);
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U)) {
assert(BO->getOpcode() == Instruction::And);
// Replace (mul & mask) --> zext (mul.with.overflow & short_mask)
ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
APInt ShortMask = CI->getValue().trunc(MulWidth);
Value *ShortAnd = Builder.CreateAnd(Mul, ShortMask);
Instruction *Zext =
cast<Instruction>(Builder.CreateZExt(ShortAnd, BO->getType()));
IC.Worklist.Add(Zext);
IC.replaceInstUsesWith(*BO, Zext);
} else {
llvm_unreachable("Unexpected Binary operation");
}
IC.Worklist.Add(cast<Instruction>(U));
}
}
if (isa<Instruction>(OtherVal))
IC.Worklist.Add(cast<Instruction>(OtherVal));
// The original icmp gets replaced with the overflow value, maybe inverted
// depending on predicate.
bool Inverse = false;
switch (I.getPredicate()) {
case ICmpInst::ICMP_NE:
break;
case ICmpInst::ICMP_EQ:
Inverse = true;
break;
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE:
if (I.getOperand(0) == MulVal)
break;
Inverse = true;
break;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE:
if (I.getOperand(1) == MulVal)
break;
Inverse = true;
break;
default:
llvm_unreachable("Unexpected predicate");
}
if (Inverse) {
Value *Res = Builder.CreateExtractValue(Call, 1);
return BinaryOperator::CreateNot(Res);
}
return ExtractValueInst::Create(Call, 1);
}
/// When performing a comparison against a constant, it is possible that not all
/// the bits in the LHS are demanded. This helper method computes the mask that
/// IS demanded.
static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth,
bool isSignCheck) {
if (isSignCheck)
return APInt::getSignMask(BitWidth);
ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand(1));
if (!CI) return APInt::getAllOnesValue(BitWidth);
const APInt &RHS = CI->getValue();
switch (I.getPredicate()) {
// For a UGT comparison, we don't care about any bits that
// correspond to the trailing ones of the comparand. The value of these
// bits doesn't impact the outcome of the comparison, because any value
// greater than the RHS must differ in a bit higher than these due to carry.
case ICmpInst::ICMP_UGT: {
unsigned trailingOnes = RHS.countTrailingOnes();
return APInt::getBitsSetFrom(BitWidth, trailingOnes);
}
// Similarly, for a ULT comparison, we don't care about the trailing zeros.
// Any value less than the RHS must differ in a higher bit because of carries.
case ICmpInst::ICMP_ULT: {
unsigned trailingZeros = RHS.countTrailingZeros();
return APInt::getBitsSetFrom(BitWidth, trailingZeros);
}
default:
return APInt::getAllOnesValue(BitWidth);
}
}
/// \brief Check if the order of \p Op0 and \p Op1 as operand in an ICmpInst
/// should be swapped.
/// The decision is based on how many times these two operands are reused
/// as subtract operands and their positions in those instructions.
/// The rational is that several architectures use the same instruction for
/// both subtract and cmp, thus it is better if the order of those operands
/// match.
/// \return true if Op0 and Op1 should be swapped.
static bool swapMayExposeCSEOpportunities(const Value * Op0,
const Value * Op1) {
// Filter out pointer value as those cannot appears directly in subtract.
// FIXME: we may want to go through inttoptrs or bitcasts.
if (Op0->getType()->isPointerTy())
return false;
// Count every uses of both Op0 and Op1 in a subtract.
// Each time Op0 is the first operand, count -1: swapping is bad, the
// subtract has already the same layout as the compare.
// Each time Op0 is the second operand, count +1: swapping is good, the
// subtract has a different layout as the compare.
// At the end, if the benefit is greater than 0, Op0 should come second to
// expose more CSE opportunities.
int GlobalSwapBenefits = 0;
for (const User *U : Op0->users()) {
const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(U);
if (!BinOp || BinOp->getOpcode() != Instruction::Sub)
continue;
// If Op0 is the first argument, this is not beneficial to swap the
// arguments.
int LocalSwapBenefits = -1;
unsigned Op1Idx = 1;
if (BinOp->getOperand(Op1Idx) == Op0) {
Op1Idx = 0;
LocalSwapBenefits = 1;
}
if (BinOp->getOperand(Op1Idx) != Op1)
continue;
GlobalSwapBenefits += LocalSwapBenefits;
}
return GlobalSwapBenefits > 0;
}
/// \brief Check that one use is in the same block as the definition and all
/// other uses are in blocks dominated by a given block.
///
/// \param DI Definition
/// \param UI Use
/// \param DB Block that must dominate all uses of \p DI outside
/// the parent block
/// \return true when \p UI is the only use of \p DI in the parent block
/// and all other uses of \p DI are in blocks dominated by \p DB.
///
bool InstCombiner::dominatesAllUses(const Instruction *DI,
const Instruction *UI,
const BasicBlock *DB) const {
assert(DI && UI && "Instruction not defined\n");
// Ignore incomplete definitions.
if (!DI->getParent())
return false;
// DI and UI must be in the same block.
if (DI->getParent() != UI->getParent())
return false;
// Protect from self-referencing blocks.
if (DI->getParent() == DB)
return false;
for (const User *U : DI->users()) {
auto *Usr = cast<Instruction>(U);
if (Usr != UI && !DT.dominates(DB, Usr->getParent()))
return false;
}
return true;
}
/// Return true when the instruction sequence within a block is select-cmp-br.
static bool isChainSelectCmpBranch(const SelectInst *SI) {
const BasicBlock *BB = SI->getParent();
if (!BB)
return false;
auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
if (!BI || BI->getNumSuccessors() != 2)
return false;
auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
return false;
return true;
}
/// \brief True when a select result is replaced by one of its operands
/// in select-icmp sequence. This will eventually result in the elimination
/// of the select.
///
/// \param SI Select instruction
/// \param Icmp Compare instruction
/// \param SIOpd Operand that replaces the select
///
/// Notes:
/// - The replacement is global and requires dominator information
/// - The caller is responsible for the actual replacement
///
/// Example:
///
/// entry:
/// %4 = select i1 %3, %C* %0, %C* null
/// %5 = icmp eq %C* %4, null
/// br i1 %5, label %9, label %7
/// ...
/// ; <label>:7 ; preds = %entry
/// %8 = getelementptr inbounds %C* %4, i64 0, i32 0
/// ...
///
/// can be transformed to
///
/// %5 = icmp eq %C* %0, null
/// %6 = select i1 %3, i1 %5, i1 true
/// br i1 %6, label %9, label %7
/// ...
/// ; <label>:7 ; preds = %entry
/// %8 = getelementptr inbounds %C* %0, i64 0, i32 0 // replace by %0!
///
/// Similar when the first operand of the select is a constant or/and
/// the compare is for not equal rather than equal.
///
/// NOTE: The function is only called when the select and compare constants
/// are equal, the optimization can work only for EQ predicates. This is not a
/// major restriction since a NE compare should be 'normalized' to an equal
/// compare, which usually happens in the combiner and test case
/// select-cmp-br.ll checks for it.
bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
const ICmpInst *Icmp,
const unsigned SIOpd) {
assert((SIOpd == 1 || SIOpd == 2) && "Invalid select operand!");
if (isChainSelectCmpBranch(SI) && Icmp->getPredicate() == ICmpInst::ICMP_EQ) {
BasicBlock *Succ = SI->getParent()->getTerminator()->getSuccessor(1);
// The check for the single predecessor is not the best that can be
// done. But it protects efficiently against cases like when SI's
// home block has two successors, Succ and Succ1, and Succ1 predecessor
// of Succ. Then SI can't be replaced by SIOpd because the use that gets
// replaced can be reached on either path. So the uniqueness check
// guarantees that the path all uses of SI (outside SI's parent) are on
// is disjoint from all other paths out of SI. But that information
// is more expensive to compute, and the trade-off here is in favor
// of compile-time. It should also be noticed that we check for a single
// predecessor and not only uniqueness. This to handle the situation when
// Succ and Succ1 points to the same basic block.
if (Succ->getSinglePredecessor() && dominatesAllUses(SI, Icmp, Succ)) {
NumSel++;
SI->replaceUsesOutsideBlock(SI->getOperand(SIOpd), SI->getParent());
return true;
}
}
return false;
}
/// Try to fold the comparison based on range information we can get by checking
/// whether bits are known to be zero or one in the inputs.
Instruction *InstCombiner::foldICmpUsingKnownBits(ICmpInst &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
Type *Ty = Op0->getType();
ICmpInst::Predicate Pred = I.getPredicate();
// Get scalar or pointer size.
unsigned BitWidth = Ty->isIntOrIntVectorTy()
? Ty->getScalarSizeInBits()
: DL.getTypeSizeInBits(Ty->getScalarType());
if (!BitWidth)
return nullptr;
// If this is a normal comparison, it demands all bits. If it is a sign bit
// comparison, it only demands the sign bit.
bool IsSignBit = false;
const APInt *CmpC;
if (match(Op1, m_APInt(CmpC))) {
bool UnusedBit;
IsSignBit = isSignBitCheck(Pred, *CmpC, UnusedBit);
}
KnownBits Op0Known(BitWidth);
KnownBits Op1Known(BitWidth);
if (SimplifyDemandedBits(&I, 0,
getDemandedBitsLHSMask(I, BitWidth, IsSignBit),
Op0Known, 0))
return &I;
if (SimplifyDemandedBits(&I, 1, APInt::getAllOnesValue(BitWidth),
Op1Known, 0))
return &I;
// Given the known and unknown bits, compute a range that the LHS could be
// in. Compute the Min, Max and RHS values based on the known bits. For the
// EQ and NE we use unsigned values.
APInt Op0Min(BitWidth, 0), Op0Max(BitWidth, 0);
APInt Op1Min(BitWidth, 0), Op1Max(BitWidth, 0);
if (I.isSigned()) {
computeSignedMinMaxValuesFromKnownBits(Op0Known, Op0Min, Op0Max);
computeSignedMinMaxValuesFromKnownBits(Op1Known, Op1Min, Op1Max);
} else {
computeUnsignedMinMaxValuesFromKnownBits(Op0Known, Op0Min, Op0Max);
computeUnsignedMinMaxValuesFromKnownBits(Op1Known, Op1Min, Op1Max);
}
// If Min and Max are known to be the same, then SimplifyDemandedBits
// figured out that the LHS is a constant. Constant fold this now, so that
// code below can assume that Min != Max.
if (!isa<Constant>(Op0) && Op0Min == Op0Max)
return new ICmpInst(Pred, ConstantInt::get(Op0->getType(), Op0Min), Op1);
if (!isa<Constant>(Op1) && Op1Min == Op1Max)
return new ICmpInst(Pred, Op0, ConstantInt::get(Op1->getType(), Op1Min));
// Based on the range information we know about the LHS, see if we can
// simplify this comparison. For example, (x&4) < 8 is always true.
switch (Pred) {
default:
llvm_unreachable("Unknown icmp opcode!");
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE: {
if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) {
return Pred == CmpInst::ICMP_EQ
? replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()))
: replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
}
// If all bits are known zero except for one, then we know at most one bit
// is set. If the comparison is against zero, then this is a check to see if
// *that* bit is set.
APInt Op0KnownZeroInverted = ~Op0Known.Zero;
if (Op1Known.isZero()) {
// If the LHS is an AND with the same constant, look through it.
Value *LHS = nullptr;
const APInt *LHSC;
if (!match(Op0, m_And(m_Value(LHS), m_APInt(LHSC))) ||
*LHSC != Op0KnownZeroInverted)
LHS = Op0;
Value *X;
if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
APInt ValToCheck = Op0KnownZeroInverted;
Type *XTy = X->getType();
if (ValToCheck.isPowerOf2()) {
// ((1 << X) & 8) == 0 -> X != 3
// ((1 << X) & 8) != 0 -> X == 3
auto *CmpC = ConstantInt::get(XTy, ValToCheck.countTrailingZeros());
auto NewPred = ICmpInst::getInversePredicate(Pred);
return new ICmpInst(NewPred, X, CmpC);
} else if ((++ValToCheck).isPowerOf2()) {
// ((1 << X) & 7) == 0 -> X >= 3
// ((1 << X) & 7) != 0 -> X < 3
auto *CmpC = ConstantInt::get(XTy, ValToCheck.countTrailingZeros());
auto NewPred =
Pred == CmpInst::ICMP_EQ ? CmpInst::ICMP_UGE : CmpInst::ICMP_ULT;
return new ICmpInst(NewPred, X, CmpC);
}
}
// Check if the LHS is 8 >>u x and the result is a power of 2 like 1.
const APInt *CI;
if (Op0KnownZeroInverted.isOneValue() &&
match(LHS, m_LShr(m_Power2(CI), m_Value(X)))) {
// ((8 >>u X) & 1) == 0 -> X != 3
// ((8 >>u X) & 1) != 0 -> X == 3
unsigned CmpVal = CI->countTrailingZeros();
auto NewPred = ICmpInst::getInversePredicate(Pred);
return new ICmpInst(NewPred, X, ConstantInt::get(X->getType(), CmpVal));
}
}
break;
}
case ICmpInst::ICMP_ULT: {
if (Op0Max.ult(Op1Min)) // A <u B -> true if max(A) < min(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Min.uge(Op1Max)) // A <u B -> false if min(A) >= max(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
if (Op1Min == Op0Max) // A <u B -> A != B if max(A) == min(B)
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
const APInt *CmpC;
if (match(Op1, m_APInt(CmpC))) {
// A <u C -> A == C-1 if min(A)+1 == C
if (Op1Max == Op0Min + 1) {
Constant *CMinus1 = ConstantInt::get(Op0->getType(), *CmpC - 1);
return new ICmpInst(ICmpInst::ICMP_EQ, Op0, CMinus1);
}
}
break;
}
case ICmpInst::ICMP_UGT: {
if (Op0Min.ugt(Op1Max)) // A >u B -> true if min(A) > max(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Max.ule(Op1Min)) // A >u B -> false if max(A) <= max(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
if (Op1Max == Op0Min) // A >u B -> A != B if min(A) == max(B)
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
const APInt *CmpC;
if (match(Op1, m_APInt(CmpC))) {
// A >u C -> A == C+1 if max(a)-1 == C
if (*CmpC == Op0Max - 1)
return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
ConstantInt::get(Op1->getType(), *CmpC + 1));
}
break;
}
case ICmpInst::ICMP_SLT:
if (Op0Max.slt(Op1Min)) // A <s B -> true if max(A) < min(C)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Min.sge(Op1Max)) // A <s B -> false if min(A) >= max(C)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
if (Op1Min == Op0Max) // A <s B -> A != B if max(A) == min(B)
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
if (Op1Max == Op0Min + 1) // A <s C -> A == C-1 if min(A)+1 == C
return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
Builder.getInt(CI->getValue() - 1));
}
break;
case ICmpInst::ICMP_SGT:
if (Op0Min.sgt(Op1Max)) // A >s B -> true if min(A) > max(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Max.sle(Op1Min)) // A >s B -> false if max(A) <= min(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
if (Op1Max == Op0Min) // A >s B -> A != B if min(A) == max(B)
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
if (Op1Min == Op0Max - 1) // A >s C -> A == C+1 if max(A)-1 == C
return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
Builder.getInt(CI->getValue() + 1));
}
break;
case ICmpInst::ICMP_SGE:
assert(!isa<ConstantInt>(Op1) && "ICMP_SGE with ConstantInt not folded!");
if (Op0Min.sge(Op1Max)) // A >=s B -> true if min(A) >= max(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Max.slt(Op1Min)) // A >=s B -> false if max(A) < min(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
break;
case ICmpInst::ICMP_SLE:
assert(!isa<ConstantInt>(Op1) && "ICMP_SLE with ConstantInt not folded!");
if (Op0Max.sle(Op1Min)) // A <=s B -> true if max(A) <= min(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Min.sgt(Op1Max)) // A <=s B -> false if min(A) > max(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
break;
case ICmpInst::ICMP_UGE:
assert(!isa<ConstantInt>(Op1) && "ICMP_UGE with ConstantInt not folded!");
if (Op0Min.uge(Op1Max)) // A >=u B -> true if min(A) >= max(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Max.ult(Op1Min)) // A >=u B -> false if max(A) < min(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
break;
case ICmpInst::ICMP_ULE:
assert(!isa<ConstantInt>(Op1) && "ICMP_ULE with ConstantInt not folded!");
if (Op0Max.ule(Op1Min)) // A <=u B -> true if max(A) <= min(B)
return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
if (Op0Min.ugt(Op1Max)) // A <=u B -> false if min(A) > max(B)
return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
break;
}
// Turn a signed comparison into an unsigned one if both operands are known to
// have the same sign.
if (I.isSigned() &&
((Op0Known.Zero.isNegative() && Op1Known.Zero.isNegative()) ||
(Op0Known.One.isNegative() && Op1Known.One.isNegative())))
return new ICmpInst(I.getUnsignedPredicate(), Op0, Op1);
return nullptr;
}
/// If we have an icmp le or icmp ge instruction with a constant operand, turn
/// it into the appropriate icmp lt or icmp gt instruction. This transform
/// allows them to be folded in visitICmpInst.
static ICmpInst *canonicalizeCmpWithConstant(ICmpInst &I) {
ICmpInst::Predicate Pred = I.getPredicate();
if (Pred != ICmpInst::ICMP_SLE && Pred != ICmpInst::ICMP_SGE &&
Pred != ICmpInst::ICMP_ULE && Pred != ICmpInst::ICMP_UGE)
return nullptr;
Value *Op0 = I.getOperand(0);
Value *Op1 = I.getOperand(1);
auto *Op1C = dyn_cast<Constant>(Op1);
if (!Op1C)
return nullptr;
// Check if the constant operand can be safely incremented/decremented without
// overflowing/underflowing. For scalars, SimplifyICmpInst has already handled
// the edge cases for us, so we just assert on them. For vectors, we must
// handle the edge cases.
Type *Op1Type = Op1->getType();
bool IsSigned = I.isSigned();
bool IsLE = (Pred == ICmpInst::ICMP_SLE || Pred == ICmpInst::ICMP_ULE);
auto *CI = dyn_cast<ConstantInt>(Op1C);
if (CI) {
// A <= MAX -> TRUE ; A >= MIN -> TRUE
assert(IsLE ? !CI->isMaxValue(IsSigned) : !CI->isMinValue(IsSigned));
} else if (Op1Type->isVectorTy()) {
// TODO? If the edge cases for vectors were guaranteed to be handled as they
// are for scalar, we could remove the min/max checks. However, to do that,
// we would have to use insertelement/shufflevector to replace edge values.
unsigned NumElts = Op1Type->getVectorNumElements();
for (unsigned i = 0; i != NumElts; ++i) {
Constant *Elt = Op1C->getAggregateElement(i);
if (!Elt)
return nullptr;
if (isa<UndefValue>(Elt))
continue;
// Bail out if we can't determine if this constant is min/max or if we
// know that this constant is min/max.
auto *CI = dyn_cast<ConstantInt>(Elt);
if (!CI || (IsLE ? CI->isMaxValue(IsSigned) : CI->isMinValue(IsSigned)))
return nullptr;
}
} else {
// ConstantExpr?
return nullptr;
}
// Increment or decrement the constant and set the new comparison predicate:
// ULE -> ULT ; UGE -> UGT ; SLE -> SLT ; SGE -> SGT
Constant *OneOrNegOne = ConstantInt::get(Op1Type, IsLE ? 1 : -1, true);
CmpInst::Predicate NewPred = IsLE ? ICmpInst::ICMP_ULT: ICmpInst::ICMP_UGT;
NewPred = IsSigned ? ICmpInst::getSignedPredicate(NewPred) : NewPred;
return new ICmpInst(NewPred, Op0, ConstantExpr::getAdd(Op1C, OneOrNegOne));
}
/// Integer compare with boolean values can always be turned into bitwise ops.
static Instruction *canonicalizeICmpBool(ICmpInst &I,
InstCombiner::BuilderTy &Builder) {
Value *A = I.getOperand(0), *B = I.getOperand(1);
assert(A->getType()->isIntOrIntVectorTy(1) && "Bools only");
// A boolean compared to true/false can be simplified to Op0/true/false in
// 14 out of the 20 (10 predicates * 2 constants) possible combinations.
// Cases not handled by InstSimplify are always 'not' of Op0.
if (match(B, m_Zero())) {
switch (I.getPredicate()) {
case CmpInst::ICMP_EQ: // A == 0 -> !A
case CmpInst::ICMP_ULE: // A <=u 0 -> !A
case CmpInst::ICMP_SGE: // A >=s 0 -> !A
return BinaryOperator::CreateNot(A);
default:
llvm_unreachable("ICmp i1 X, C not simplified as expected.");
}
} else if (match(B, m_One())) {
switch (I.getPredicate()) {
case CmpInst::ICMP_NE: // A != 1 -> !A
case CmpInst::ICMP_ULT: // A <u 1 -> !A
case CmpInst::ICMP_SGT: // A >s -1 -> !A
return BinaryOperator::CreateNot(A);
default:
llvm_unreachable("ICmp i1 X, C not simplified as expected.");
}
}
switch (I.getPredicate()) {
default:
llvm_unreachable("Invalid icmp instruction!");
case ICmpInst::ICMP_EQ:
// icmp eq i1 A, B -> ~(A ^ B)
return BinaryOperator::CreateNot(Builder.CreateXor(A, B));
case ICmpInst::ICMP_NE:
// icmp ne i1 A, B -> A ^ B
return BinaryOperator::CreateXor(A, B);
case ICmpInst::ICMP_UGT:
// icmp ugt -> icmp ult
std::swap(A, B);
LLVM_FALLTHROUGH;
case ICmpInst::ICMP_ULT:
// icmp ult i1 A, B -> ~A & B
return BinaryOperator::CreateAnd(Builder.CreateNot(A), B);
case ICmpInst::ICMP_SGT:
// icmp sgt -> icmp slt
std::swap(A, B);
LLVM_FALLTHROUGH;
case ICmpInst::ICMP_SLT:
// icmp slt i1 A, B -> A & ~B
return BinaryOperator::CreateAnd(Builder.CreateNot(B), A);
case ICmpInst::ICMP_UGE:
// icmp uge -> icmp ule
std::swap(A, B);
LLVM_FALLTHROUGH;
case ICmpInst::ICMP_ULE:
// icmp ule i1 A, B -> ~A | B
return BinaryOperator::CreateOr(Builder.CreateNot(A), B);
case ICmpInst::ICMP_SGE:
// icmp sge -> icmp sle
std::swap(A, B);
LLVM_FALLTHROUGH;
case ICmpInst::ICMP_SLE:
// icmp sle i1 A, B -> A | ~B
return BinaryOperator::CreateOr(Builder.CreateNot(B), A);
}
}
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
unsigned Op0Cplxity = getComplexity(Op0);
unsigned Op1Cplxity = getComplexity(Op1);
/// Orders the operands of the compare so that they are listed from most
/// complex to least complex. This puts constants before unary operators,
/// before binary operators.
if (Op0Cplxity < Op1Cplxity ||
(Op0Cplxity == Op1Cplxity && swapMayExposeCSEOpportunities(Op0, Op1))) {
I.swapOperands();
std::swap(Op0, Op1);
Changed = true;
}
if (Value *V = SimplifyICmpInst(I.getPredicate(), Op0, Op1,
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
// Comparing -val or val with non-zero is the same as just comparing val
// ie, abs(val) != 0 -> val != 0
if (I.getPredicate() == ICmpInst::ICMP_NE && match(Op1, m_Zero())) {
Value *Cond, *SelectTrue, *SelectFalse;
if (match(Op0, m_Select(m_Value(Cond), m_Value(SelectTrue),
m_Value(SelectFalse)))) {
if (Value *V = dyn_castNegVal(SelectTrue)) {
if (V == SelectFalse)
return CmpInst::Create(Instruction::ICmp, I.getPredicate(), V, Op1);
}
else if (Value *V = dyn_castNegVal(SelectFalse)) {
if (V == SelectTrue)
return CmpInst::Create(Instruction::ICmp, I.getPredicate(), V, Op1);
}
}
}
if (Op0->getType()->isIntOrIntVectorTy(1))
if (Instruction *Res = canonicalizeICmpBool(I, Builder))
return Res;
if (ICmpInst *NewICmp = canonicalizeCmpWithConstant(I))
return NewICmp;
if (Instruction *Res = foldICmpWithConstant(I))
return Res;
if (Instruction *Res = foldICmpUsingKnownBits(I))
return Res;
// Test if the ICmpInst instruction is used exclusively by a select as
// part of a minimum or maximum operation. If so, refrain from doing
// any other folding. This helps out other analyses which understand
// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
// and CodeGen. And in this case, at least one of the comparison
// operands has at least one user besides the compare (the select),
// which would often largely negate the benefit of folding anyway.
if (I.hasOneUse())
if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
return nullptr;
// FIXME: We only do this after checking for min/max to prevent infinite
// looping caused by a reverse canonicalization of these patterns for min/max.
// FIXME: The organization of folds is a mess. These would naturally go into
// canonicalizeCmpWithConstant(), but we can't move all of the above folds
// down here after the min/max restriction.
ICmpInst::Predicate Pred = I.getPredicate();
const APInt *C;
if (match(Op1, m_APInt(C))) {
// For i32: x >u 2147483647 -> x <s 0 -> true if sign bit set
if (Pred == ICmpInst::ICMP_UGT && C->isMaxSignedValue()) {
Constant *Zero = Constant::getNullValue(Op0->getType());
return new ICmpInst(ICmpInst::ICMP_SLT, Op0, Zero);
}
// For i32: x <u 2147483648 -> x >s -1 -> true if sign bit clear
if (Pred == ICmpInst::ICMP_ULT && C->isMinSignedValue()) {
Constant *AllOnes = Constant::getAllOnesValue(Op0->getType());
return new ICmpInst(ICmpInst::ICMP_SGT, Op0, AllOnes);
}
}
if (Instruction *Res = foldICmpInstWithConstant(I))
return Res;
if (Instruction *Res = foldICmpInstWithConstantNotInt(I))
return Res;
// If we can optimize a 'icmp GEP, P' or 'icmp P, GEP', do so now.
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op0))
if (Instruction *NI = foldGEPICmp(GEP, Op1, I.getPredicate(), I))
return NI;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op1))
if (Instruction *NI = foldGEPICmp(GEP, Op0,
ICmpInst::getSwappedPredicate(I.getPredicate()), I))
return NI;
// Try to optimize equality comparisons against alloca-based pointers.
if (Op0->getType()->isPointerTy() && I.isEquality()) {
assert(Op1->getType()->isPointerTy() && "Comparing pointer with non-pointer?");
if (auto *Alloca = dyn_cast<AllocaInst>(GetUnderlyingObject(Op0, DL)))
if (Instruction *New = foldAllocaCmp(I, Alloca, Op1))
return New;
if (auto *Alloca = dyn_cast<AllocaInst>(GetUnderlyingObject(Op1, DL)))
if (Instruction *New = foldAllocaCmp(I, Alloca, Op0))
return New;
}
// Test to see if the operands of the icmp are casted versions of other
// values. If the ptr->ptr cast can be stripped off both arguments, we do so
// now.
if (BitCastInst *CI = dyn_cast<BitCastInst>(Op0)) {
if (Op0->getType()->isPointerTy() &&
(isa<Constant>(Op1) || isa<BitCastInst>(Op1))) {
// We keep moving the cast from the left operand over to the right
// operand, where it can often be eliminated completely.
Op0 = CI->getOperand(0);
// If operand #1 is a bitcast instruction, it must also be a ptr->ptr cast
// so eliminate it as well.
if (BitCastInst *CI2 = dyn_cast<BitCastInst>(Op1))
Op1 = CI2->getOperand(0);
// If Op1 is a constant, we can fold the cast into the constant.
if (Op0->getType() != Op1->getType()) {
if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
Op1 = ConstantExpr::getBitCast(Op1C, Op0->getType());
} else {
// Otherwise, cast the RHS right before the icmp
Op1 = Builder.CreateBitCast(Op1, Op0->getType());
}
}
return new ICmpInst(I.getPredicate(), Op0, Op1);
}
}
if (isa<CastInst>(Op0)) {
// Handle the special case of: icmp (cast bool to X), <cst>
// This comes up when you have code like
// int X = A < B;
// if (X) ...
// For generality, we handle any zero-extension of any operand comparison
// with a constant or another cast from the same type.
if (isa<Constant>(Op1) || isa<CastInst>(Op1))
if (Instruction *R = foldICmpWithCastAndCast(I))
return R;
}
if (Instruction *Res = foldICmpBinOp(I))
return Res;
if (Instruction *Res = foldICmpWithMinMax(I))
return Res;
{
Value *A, *B;
// Transform (A & ~B) == 0 --> (A & B) != 0
// and (A & ~B) != 0 --> (A & B) == 0
// if A is a power of 2.
if (match(Op0, m_And(m_Value(A), m_Not(m_Value(B)))) &&
match(Op1, m_Zero()) &&
isKnownToBeAPowerOfTwo(A, false, 0, &I) && I.isEquality())
return new ICmpInst(I.getInversePredicate(), Builder.CreateAnd(A, B),
Op1);
// ~X < ~Y --> Y < X
// ~X < C --> X > ~C
if (match(Op0, m_Not(m_Value(A)))) {
if (match(Op1, m_Not(m_Value(B))))
return new ICmpInst(I.getPredicate(), B, A);
const APInt *C;
if (match(Op1, m_APInt(C)))
return new ICmpInst(I.getSwappedPredicate(), A,
ConstantInt::get(Op1->getType(), ~(*C)));
}
Instruction *AddI = nullptr;
if (match(&I, m_UAddWithOverflow(m_Value(A), m_Value(B),
m_Instruction(AddI))) &&
isa<IntegerType>(A->getType())) {
Value *Result;
Constant *Overflow;
if (OptimizeOverflowCheck(OCF_UNSIGNED_ADD, A, B, *AddI, Result,
Overflow)) {
replaceInstUsesWith(*AddI, Result);
return replaceInstUsesWith(I, Overflow);
}
}
// (zext a) * (zext b) --> llvm.umul.with.overflow.
if (match(Op0, m_Mul(m_ZExt(m_Value(A)), m_ZExt(m_Value(B))))) {
if (Instruction *R = processUMulZExtIdiom(I, Op0, Op1, *this))
return R;
}
if (match(Op1, m_Mul(m_ZExt(m_Value(A)), m_ZExt(m_Value(B))))) {
if (Instruction *R = processUMulZExtIdiom(I, Op1, Op0, *this))
return R;
}
}
if (Instruction *Res = foldICmpEquality(I))
return Res;
// The 'cmpxchg' instruction returns an aggregate containing the old value and
// an i1 which indicates whether or not we successfully did the swap.
//
// Replace comparisons between the old value and the expected value with the
// indicator that 'cmpxchg' returns.
//
// N.B. This transform is only valid when the 'cmpxchg' is not permitted to
// spuriously fail. In those cases, the old value may equal the expected
// value but it is possible for the swap to not occur.
if (I.getPredicate() == ICmpInst::ICMP_EQ)
if (auto *EVI = dyn_cast<ExtractValueInst>(Op0))
if (auto *ACXI = dyn_cast<AtomicCmpXchgInst>(EVI->getAggregateOperand()))
if (EVI->getIndices()[0] == 0 && ACXI->getCompareOperand() == Op1 &&
!ACXI->isWeak())
return ExtractValueInst::Create(ACXI, 1);
{
Value *X; ConstantInt *Cst;
// icmp X+Cst, X
if (match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op1 == X)
return foldICmpAddOpConst(X, Cst, I.getPredicate());
// icmp X, X+Cst
if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
return foldICmpAddOpConst(X, Cst, I.getSwappedPredicate());
}
return Changed ? &I : nullptr;
}
/// Fold fcmp ([us]itofp x, cst) if possible.
Instruction *InstCombiner::foldFCmpIntToFPConst(FCmpInst &I, Instruction *LHSI,
Constant *RHSC) {
if (!isa<ConstantFP>(RHSC)) return nullptr;
const APFloat &RHS = cast<ConstantFP>(RHSC)->getValueAPF();
// Get the width of the mantissa. We don't want to hack on conversions that
// might lose information from the integer, e.g. "i64 -> float"
int MantissaWidth = LHSI->getType()->getFPMantissaWidth();
if (MantissaWidth == -1) return nullptr; // Unknown.
IntegerType *IntTy = cast<IntegerType>(LHSI->getOperand(0)->getType());
bool LHSUnsigned = isa<UIToFPInst>(LHSI);
if (I.isEquality()) {
FCmpInst::Predicate P = I.getPredicate();
bool IsExact = false;
APSInt RHSCvt(IntTy->getBitWidth(), LHSUnsigned);
RHS.convertToInteger(RHSCvt, APFloat::rmNearestTiesToEven, &IsExact);
// If the floating point constant isn't an integer value, we know if we will
// ever compare equal / not equal to it.
if (!IsExact) {
// TODO: Can never be -0.0 and other non-representable values
APFloat RHSRoundInt(RHS);
RHSRoundInt.roundToIntegral(APFloat::rmNearestTiesToEven);
if (RHS.compare(RHSRoundInt) != APFloat::cmpEqual) {
if (P == FCmpInst::FCMP_OEQ || P == FCmpInst::FCMP_UEQ)
return replaceInstUsesWith(I, Builder.getFalse());
assert(P == FCmpInst::FCMP_ONE || P == FCmpInst::FCMP_UNE);
return replaceInstUsesWith(I, Builder.getTrue());
}
}
// TODO: If the constant is exactly representable, is it always OK to do
// equality compares as integer?
}
// Check to see that the input is converted from an integer type that is small
// enough that preserves all bits. TODO: check here for "known" sign bits.
// This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e.
unsigned InputSize = IntTy->getScalarSizeInBits();
// Following test does NOT adjust InputSize downwards for signed inputs,
// because the most negative value still requires all the mantissa bits
// to distinguish it from one less than that value.
if ((int)InputSize > MantissaWidth) {
// Conversion would lose accuracy. Check if loss can impact comparison.
int Exp = ilogb(RHS);
if (Exp == APFloat::IEK_Inf) {
int MaxExponent = ilogb(APFloat::getLargest(RHS.getSemantics()));
if (MaxExponent < (int)InputSize - !LHSUnsigned)
// Conversion could create infinity.
return nullptr;
} else {
// Note that if RHS is zero or NaN, then Exp is negative
// and first condition is trivially false.
if (MantissaWidth <= Exp && Exp <= (int)InputSize - !LHSUnsigned)
// Conversion could affect comparison.
return nullptr;
}
}
// Otherwise, we can potentially simplify the comparison. We know that it
// will always come through as an integer value and we know the constant is
// not a NAN (it would have been previously simplified).
assert(!RHS.isNaN() && "NaN comparison not already folded!");
ICmpInst::Predicate Pred;
switch (I.getPredicate()) {
default: llvm_unreachable("Unexpected predicate!");
case FCmpInst::FCMP_UEQ:
case FCmpInst::FCMP_OEQ:
Pred = ICmpInst::ICMP_EQ;
break;
case FCmpInst::FCMP_UGT:
case FCmpInst::FCMP_OGT:
Pred = LHSUnsigned ? ICmpInst::ICMP_UGT : ICmpInst::ICMP_SGT;
break;
case FCmpInst::FCMP_UGE:
case FCmpInst::FCMP_OGE:
Pred = LHSUnsigned ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_SGE;
break;
case FCmpInst::FCMP_ULT:
case FCmpInst::FCMP_OLT:
Pred = LHSUnsigned ? ICmpInst::ICMP_ULT : ICmpInst::ICMP_SLT;
break;
case FCmpInst::FCMP_ULE:
case FCmpInst::FCMP_OLE:
Pred = LHSUnsigned ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_SLE;
break;
case FCmpInst::FCMP_UNE:
case FCmpInst::FCMP_ONE:
Pred = ICmpInst::ICMP_NE;
break;
case FCmpInst::FCMP_ORD:
return replaceInstUsesWith(I, Builder.getTrue());
case FCmpInst::FCMP_UNO:
return replaceInstUsesWith(I, Builder.getFalse());
}
// Now we know that the APFloat is a normal number, zero or inf.
// See if the FP constant is too large for the integer. For example,
// comparing an i8 to 300.0.
unsigned IntWidth = IntTy->getScalarSizeInBits();
if (!LHSUnsigned) {
// If the RHS value is > SignedMax, fold the comparison. This handles +INF
// and large values.
APFloat SMax(RHS.getSemantics());
SMax.convertFromAPInt(APInt::getSignedMaxValue(IntWidth), true,
APFloat::rmNearestTiesToEven);
if (SMax.compare(RHS) == APFloat::cmpLessThan) { // smax < 13123.0
if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SLT ||
Pred == ICmpInst::ICMP_SLE)
return replaceInstUsesWith(I, Builder.getTrue());
return replaceInstUsesWith(I, Builder.getFalse());
}
} else {
// If the RHS value is > UnsignedMax, fold the comparison. This handles
// +INF and large values.
APFloat UMax(RHS.getSemantics());
UMax.convertFromAPInt(APInt::getMaxValue(IntWidth), false,
APFloat::rmNearestTiesToEven);
if (UMax.compare(RHS) == APFloat::cmpLessThan) { // umax < 13123.0
if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_ULT ||
Pred == ICmpInst::ICMP_ULE)
return replaceInstUsesWith(I, Builder.getTrue());
return replaceInstUsesWith(I, Builder.getFalse());
}
}
if (!LHSUnsigned) {
// See if the RHS value is < SignedMin.
APFloat SMin(RHS.getSemantics());
SMin.convertFromAPInt(APInt::getSignedMinValue(IntWidth), true,
APFloat::rmNearestTiesToEven);
if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // smin > 12312.0
if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SGT ||
Pred == ICmpInst::ICMP_SGE)
return replaceInstUsesWith(I, Builder.getTrue());
return replaceInstUsesWith(I, Builder.getFalse());
}
} else {
// See if the RHS value is < UnsignedMin.
APFloat SMin(RHS.getSemantics());
SMin.convertFromAPInt(APInt::getMinValue(IntWidth), true,
APFloat::rmNearestTiesToEven);
if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // umin > 12312.0
if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_UGT ||
Pred == ICmpInst::ICMP_UGE)
return replaceInstUsesWith(I, Builder.getTrue());
return replaceInstUsesWith(I, Builder.getFalse());
}
}
// Okay, now we know that the FP constant fits in the range [SMIN, SMAX] or
// [0, UMAX], but it may still be fractional. See if it is fractional by
// casting the FP value to the integer value and back, checking for equality.
// Don't do this for zero, because -0.0 is not fractional.
Constant *RHSInt = LHSUnsigned
? ConstantExpr::getFPToUI(RHSC, IntTy)
: ConstantExpr::getFPToSI(RHSC, IntTy);
if (!RHS.isZero()) {
bool Equal = LHSUnsigned
? ConstantExpr::getUIToFP(RHSInt, RHSC->getType()) == RHSC
: ConstantExpr::getSIToFP(RHSInt, RHSC->getType()) == RHSC;
if (!Equal) {
// If we had a comparison against a fractional value, we have to adjust
// the compare predicate and sometimes the value. RHSC is rounded towards
// zero at this point.
switch (Pred) {
default: llvm_unreachable("Unexpected integer comparison!");
case ICmpInst::ICMP_NE: // (float)int != 4.4 --> true
return replaceInstUsesWith(I, Builder.getTrue());
case ICmpInst::ICMP_EQ: // (float)int == 4.4 --> false
return replaceInstUsesWith(I, Builder.getFalse());
case ICmpInst::ICMP_ULE:
// (float)int <= 4.4 --> int <= 4
// (float)int <= -4.4 --> false
if (RHS.isNegative())
return replaceInstUsesWith(I, Builder.getFalse());
break;
case ICmpInst::ICMP_SLE:
// (float)int <= 4.4 --> int <= 4
// (float)int <= -4.4 --> int < -4
if (RHS.isNegative())
Pred = ICmpInst::ICMP_SLT;
break;
case ICmpInst::ICMP_ULT:
// (float)int < -4.4 --> false
// (float)int < 4.4 --> int <= 4
if (RHS.isNegative())
return replaceInstUsesWith(I, Builder.getFalse());
Pred = ICmpInst::ICMP_ULE;
break;
case ICmpInst::ICMP_SLT:
// (float)int < -4.4 --> int < -4
// (float)int < 4.4 --> int <= 4
if (!RHS.isNegative())
Pred = ICmpInst::ICMP_SLE;
break;
case ICmpInst::ICMP_UGT:
// (float)int > 4.4 --> int > 4
// (float)int > -4.4 --> true
if (RHS.isNegative())
return replaceInstUsesWith(I, Builder.getTrue());
break;
case ICmpInst::ICMP_SGT:
// (float)int > 4.4 --> int > 4
// (float)int > -4.4 --> int >= -4
if (RHS.isNegative())
Pred = ICmpInst::ICMP_SGE;
break;
case ICmpInst::ICMP_UGE:
// (float)int >= -4.4 --> true
// (float)int >= 4.4 --> int > 4
if (RHS.isNegative())
return replaceInstUsesWith(I, Builder.getTrue());
Pred = ICmpInst::ICMP_UGT;
break;
case ICmpInst::ICMP_SGE:
// (float)int >= -4.4 --> int >= -4
// (float)int >= 4.4 --> int > 4
if (!RHS.isNegative())
Pred = ICmpInst::ICMP_SGT;
break;
}
}
}
// Lower this FP comparison into an appropriate integer version of the
// comparison.
return new ICmpInst(Pred, LHSI->getOperand(0), RHSInt);
}
Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
bool Changed = false;
/// Orders the operands of the compare so that they are listed from most
/// complex to least complex. This puts constants before unary operators,
/// before binary operators.
if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) {
I.swapOperands();
Changed = true;
}
const CmpInst::Predicate Pred = I.getPredicate();
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyFCmpInst(Pred, Op0, Op1, I.getFastMathFlags(),
SQ.getWithInstruction(&I)))
return replaceInstUsesWith(I, V);
// Simplify 'fcmp pred X, X'
if (Op0 == Op1) {
switch (Pred) {
default: break;
case FCmpInst::FCMP_UNO: // True if unordered: isnan(X) | isnan(Y)
case FCmpInst::FCMP_ULT: // True if unordered or less than
case FCmpInst::FCMP_UGT: // True if unordered or greater than
case FCmpInst::FCMP_UNE: // True if unordered or not equal
// Canonicalize these to be 'fcmp uno %X, 0.0'.
I.setPredicate(FCmpInst::FCMP_UNO);
I.setOperand(1, Constant::getNullValue(Op0->getType()));
return &I;
case FCmpInst::FCMP_ORD: // True if ordered (no nans)
case FCmpInst::FCMP_OEQ: // True if ordered and equal
case FCmpInst::FCMP_OGE: // True if ordered and greater than or equal
case FCmpInst::FCMP_OLE: // True if ordered and less than or equal
// Canonicalize these to be 'fcmp ord %X, 0.0'.
I.setPredicate(FCmpInst::FCMP_ORD);
I.setOperand(1, Constant::getNullValue(Op0->getType()));
return &I;
}
}
// If we're just checking for a NaN (ORD/UNO) and have a non-NaN operand,
// then canonicalize the operand to 0.0.
if (Pred == CmpInst::FCMP_ORD || Pred == CmpInst::FCMP_UNO) {
if (!match(Op0, m_Zero()) && isKnownNeverNaN(Op0)) {
I.setOperand(0, ConstantFP::getNullValue(Op0->getType()));
return &I;
}
if (!match(Op1, m_Zero()) && isKnownNeverNaN(Op1)) {
I.setOperand(1, ConstantFP::getNullValue(Op0->getType()));
return &I;
}
}
// Test if the FCmpInst instruction is used exclusively by a select as
// part of a minimum or maximum operation. If so, refrain from doing
// any other folding. This helps out other analyses which understand
// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
// and CodeGen. And in this case, at least one of the comparison
// operands has at least one user besides the compare (the select),
// which would often largely negate the benefit of folding anyway.
if (I.hasOneUse())
if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
return nullptr;
// Handle fcmp with constant RHS
if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
switch (LHSI->getOpcode()) {
case Instruction::FPExt: {
// fcmp (fpext x), C -> fcmp x, (fptrunc C) if fptrunc is lossless
FPExtInst *LHSExt = cast<FPExtInst>(LHSI);
ConstantFP *RHSF = dyn_cast<ConstantFP>(RHSC);
if (!RHSF)
break;
const fltSemantics *Sem;
// FIXME: This shouldn't be here.
if (LHSExt->getSrcTy()->isHalfTy())
Sem = &APFloat::IEEEhalf();
else if (LHSExt->getSrcTy()->isFloatTy())
Sem = &APFloat::IEEEsingle();
else if (LHSExt->getSrcTy()->isDoubleTy())
Sem = &APFloat::IEEEdouble();
else if (LHSExt->getSrcTy()->isFP128Ty())
Sem = &APFloat::IEEEquad();
else if (LHSExt->getSrcTy()->isX86_FP80Ty())
Sem = &APFloat::x87DoubleExtended();
else if (LHSExt->getSrcTy()->isPPC_FP128Ty())
Sem = &APFloat::PPCDoubleDouble();
else
break;
bool Lossy;
APFloat F = RHSF->getValueAPF();
F.convert(*Sem, APFloat::rmNearestTiesToEven, &Lossy);
// Avoid lossy conversions and denormals. Zero is a special case
// that's OK to convert.
APFloat Fabs = F;
Fabs.clearSign();
if (!Lossy &&
((Fabs.compare(APFloat::getSmallestNormalized(*Sem)) !=
APFloat::cmpLessThan) || Fabs.isZero()))
return new FCmpInst(Pred, LHSExt->getOperand(0),
ConstantFP::get(RHSC->getContext(), F));
break;
}
case Instruction::PHI:
// Only fold fcmp into the PHI if the phi and fcmp are in the same
// block. If in the same block, we're encouraging jump threading. If
// not, we are just pessimizing the code by making an i1 phi.
if (LHSI->getParent() == I.getParent())
if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
return NV;
break;
case Instruction::SIToFP:
case Instruction::UIToFP:
if (Instruction *NV = foldFCmpIntToFPConst(I, LHSI, RHSC))
return NV;
break;
case Instruction::FSub: {
// fcmp pred (fneg x), C -> fcmp swap(pred) x, -C
Value *Op;
if (match(LHSI, m_FNeg(m_Value(Op))))
return new FCmpInst(I.getSwappedPredicate(), Op,
ConstantExpr::getFNeg(RHSC));
break;
}
case Instruction::Load:
if (GetElementPtrInst *GEP =
dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
!cast<LoadInst>(LHSI)->isVolatile())
if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
return Res;
}
break;
case Instruction::Call: {
if (!RHSC->isNullValue())
break;
CallInst *CI = cast<CallInst>(LHSI);
Intrinsic::ID IID = getIntrinsicForCallSite(CI, &TLI);
if (IID != Intrinsic::fabs)
break;
// Various optimization for fabs compared with zero.
switch (Pred) {
default:
break;
// fabs(x) < 0 --> false
case FCmpInst::FCMP_OLT:
llvm_unreachable("handled by SimplifyFCmpInst");
// fabs(x) > 0 --> x != 0
case FCmpInst::FCMP_OGT:
return new FCmpInst(FCmpInst::FCMP_ONE, CI->getArgOperand(0), RHSC);
// fabs(x) <= 0 --> x == 0
case FCmpInst::FCMP_OLE:
return new FCmpInst(FCmpInst::FCMP_OEQ, CI->getArgOperand(0), RHSC);
// fabs(x) >= 0 --> !isnan(x)
case FCmpInst::FCMP_OGE:
return new FCmpInst(FCmpInst::FCMP_ORD, CI->getArgOperand(0), RHSC);
// fabs(x) == 0 --> x == 0
// fabs(x) != 0 --> x != 0
case FCmpInst::FCMP_OEQ:
case FCmpInst::FCMP_UEQ:
case FCmpInst::FCMP_ONE:
case FCmpInst::FCMP_UNE:
return new FCmpInst(Pred, CI->getArgOperand(0), RHSC);
}
}
}
}
// fcmp pred (fneg x), (fneg y) -> fcmp swap(pred) x, y
Value *X, *Y;
if (match(Op0, m_FNeg(m_Value(X))) && match(Op1, m_FNeg(m_Value(Y))))
return new FCmpInst(I.getSwappedPredicate(), X, Y);
// fcmp (fpext x), (fpext y) -> fcmp x, y
if (FPExtInst *LHSExt = dyn_cast<FPExtInst>(Op0))
if (FPExtInst *RHSExt = dyn_cast<FPExtInst>(Op1))
if (LHSExt->getSrcTy() == RHSExt->getSrcTy())
return new FCmpInst(Pred, LHSExt->getOperand(0), RHSExt->getOperand(0));
return Changed ? &I : nullptr;
}
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