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llvm-project/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

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//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation analyzes and transforms the induction variables (and
// computations derived from them) into forms suitable for efficient execution
// on the target.
//
// This pass performs a strength reduction on array references inside loops that
// have as one or more of their components the loop induction variable, it
// rewrites expressions to take advantage of scaled-index addressing modes
// available on the target, and it performs a variety of other optimizations
// related to loop induction variables.
//
// Terminology note: this code has a lot of handling for "post-increment" or
// "post-inc" users. This is not talking about post-increment addressing modes;
// it is instead talking about code like this:
//
// %i = phi [ 0, %entry ], [ %i.next, %latch ]
// ...
// %i.next = add %i, 1
// %c = icmp eq %i.next, %n
//
// The SCEV for %i is {0,+,1}<%L>. The SCEV for %i.next is {1,+,1}<%L>, however
// it's useful to think about these as the same register, with some uses using
// the value of the register before the add and some using it after. In this
// example, the icmp is a post-increment user, since it uses %i.next, which is
// the value of the induction variable after the increment. The other common
// case of post-increment users is users outside the loop.
//
// TODO: More sophistication in the way Formulae are generated and filtered.
//
// TODO: Handle multiple loops at a time.
//
// TODO: Should the addressing mode BaseGV be changed to a ConstantExpr instead
// of a GlobalValue?
//
// TODO: When truncation is free, truncate ICmp users' operands to make it a
// smaller encoding (on x86 at least).
//
// TODO: When a negated register is used by an add (such as in a list of
// multiple base registers, or as the increment expression in an addrec),
// we may not actually need both reg and (-1 * reg) in registers; the
// negation can be implemented by using a sub instead of an add. The
// lack of support for taking this into consideration when making
// register pressure decisions is partly worked around by the "Special"
// use kind.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LoopStrengthReduce.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/LoopPassManager.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
using namespace llvm;
#define DEBUG_TYPE "loop-reduce"
/// MaxIVUsers is an arbitrary threshold that provides an early opportunitiy for
/// bail out. This threshold is far beyond the number of users that LSR can
/// conceivably solve, so it should not affect generated code, but catches the
/// worst cases before LSR burns too much compile time and stack space.
static const unsigned MaxIVUsers = 200;
// Temporary flag to cleanup congruent phis after LSR phi expansion.
// It's currently disabled until we can determine whether it's truly useful or
// not. The flag should be removed after the v3.0 release.
// This is now needed for ivchains.
static cl::opt<bool> EnablePhiElim(
"enable-lsr-phielim", cl::Hidden, cl::init(true),
cl::desc("Enable LSR phi elimination"));
#ifndef NDEBUG
// Stress test IV chain generation.
static cl::opt<bool> StressIVChain(
"stress-ivchain", cl::Hidden, cl::init(false),
cl::desc("Stress test LSR IV chains"));
#else
static bool StressIVChain = false;
#endif
namespace {
struct MemAccessTy {
/// Used in situations where the accessed memory type is unknown.
static const unsigned UnknownAddressSpace = ~0u;
Type *MemTy;
unsigned AddrSpace;
MemAccessTy() : MemTy(nullptr), AddrSpace(UnknownAddressSpace) {}
MemAccessTy(Type *Ty, unsigned AS) :
MemTy(Ty), AddrSpace(AS) {}
bool operator==(MemAccessTy Other) const {
return MemTy == Other.MemTy && AddrSpace == Other.AddrSpace;
}
bool operator!=(MemAccessTy Other) const { return !(*this == Other); }
static MemAccessTy getUnknown(LLVMContext &Ctx) {
return MemAccessTy(Type::getVoidTy(Ctx), UnknownAddressSpace);
}
};
/// This class holds data which is used to order reuse candidates.
class RegSortData {
public:
/// This represents the set of LSRUse indices which reference
/// a particular register.
SmallBitVector UsedByIndices;
void print(raw_ostream &OS) const;
void dump() const;
};
}
void RegSortData::print(raw_ostream &OS) const {
OS << "[NumUses=" << UsedByIndices.count() << ']';
}
LLVM_DUMP_METHOD
void RegSortData::dump() const {
print(errs()); errs() << '\n';
}
namespace {
/// Map register candidates to information about how they are used.
class RegUseTracker {
typedef DenseMap<const SCEV *, RegSortData> RegUsesTy;
RegUsesTy RegUsesMap;
SmallVector<const SCEV *, 16> RegSequence;
public:
void countRegister(const SCEV *Reg, size_t LUIdx);
void dropRegister(const SCEV *Reg, size_t LUIdx);
void swapAndDropUse(size_t LUIdx, size_t LastLUIdx);
bool isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const;
const SmallBitVector &getUsedByIndices(const SCEV *Reg) const;
void clear();
typedef SmallVectorImpl<const SCEV *>::iterator iterator;
typedef SmallVectorImpl<const SCEV *>::const_iterator const_iterator;
iterator begin() { return RegSequence.begin(); }
iterator end() { return RegSequence.end(); }
const_iterator begin() const { return RegSequence.begin(); }
const_iterator end() const { return RegSequence.end(); }
};
}
void
RegUseTracker::countRegister(const SCEV *Reg, size_t LUIdx) {
std::pair<RegUsesTy::iterator, bool> Pair =
RegUsesMap.insert(std::make_pair(Reg, RegSortData()));
RegSortData &RSD = Pair.first->second;
if (Pair.second)
RegSequence.push_back(Reg);
RSD.UsedByIndices.resize(std::max(RSD.UsedByIndices.size(), LUIdx + 1));
RSD.UsedByIndices.set(LUIdx);
}
void
RegUseTracker::dropRegister(const SCEV *Reg, size_t LUIdx) {
RegUsesTy::iterator It = RegUsesMap.find(Reg);
assert(It != RegUsesMap.end());
RegSortData &RSD = It->second;
assert(RSD.UsedByIndices.size() > LUIdx);
RSD.UsedByIndices.reset(LUIdx);
}
void
RegUseTracker::swapAndDropUse(size_t LUIdx, size_t LastLUIdx) {
assert(LUIdx <= LastLUIdx);
// Update RegUses. The data structure is not optimized for this purpose;
// we must iterate through it and update each of the bit vectors.
for (auto &Pair : RegUsesMap) {
SmallBitVector &UsedByIndices = Pair.second.UsedByIndices;
if (LUIdx < UsedByIndices.size())
UsedByIndices[LUIdx] =
LastLUIdx < UsedByIndices.size() ? UsedByIndices[LastLUIdx] : 0;
UsedByIndices.resize(std::min(UsedByIndices.size(), LastLUIdx));
}
}
bool
RegUseTracker::isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const {
RegUsesTy::const_iterator I = RegUsesMap.find(Reg);
if (I == RegUsesMap.end())
return false;
const SmallBitVector &UsedByIndices = I->second.UsedByIndices;
int i = UsedByIndices.find_first();
if (i == -1) return false;
if ((size_t)i != LUIdx) return true;
return UsedByIndices.find_next(i) != -1;
}
const SmallBitVector &RegUseTracker::getUsedByIndices(const SCEV *Reg) const {
RegUsesTy::const_iterator I = RegUsesMap.find(Reg);
assert(I != RegUsesMap.end() && "Unknown register!");
return I->second.UsedByIndices;
}
void RegUseTracker::clear() {
RegUsesMap.clear();
RegSequence.clear();
}
namespace {
/// This class holds information that describes a formula for computing
/// satisfying a use. It may include broken-out immediates and scaled registers.
struct Formula {
/// Global base address used for complex addressing.
GlobalValue *BaseGV;
/// Base offset for complex addressing.
int64_t BaseOffset;
/// Whether any complex addressing has a base register.
bool HasBaseReg;
/// The scale of any complex addressing.
int64_t Scale;
/// The list of "base" registers for this use. When this is non-empty. The
/// canonical representation of a formula is
/// 1. BaseRegs.size > 1 implies ScaledReg != NULL and
/// 2. ScaledReg != NULL implies Scale != 1 || !BaseRegs.empty().
/// #1 enforces that the scaled register is always used when at least two
/// registers are needed by the formula: e.g., reg1 + reg2 is reg1 + 1 * reg2.
/// #2 enforces that 1 * reg is reg.
/// This invariant can be temporarly broken while building a formula.
/// However, every formula inserted into the LSRInstance must be in canonical
/// form.
SmallVector<const SCEV *, 4> BaseRegs;
/// The 'scaled' register for this use. This should be non-null when Scale is
/// not zero.
const SCEV *ScaledReg;
/// An additional constant offset which added near the use. This requires a
/// temporary register, but the offset itself can live in an add immediate
/// field rather than a register.
int64_t UnfoldedOffset;
Formula()
: BaseGV(nullptr), BaseOffset(0), HasBaseReg(false), Scale(0),
ScaledReg(nullptr), UnfoldedOffset(0) {}
void initialMatch(const SCEV *S, Loop *L, ScalarEvolution &SE);
bool isCanonical() const;
void canonicalize();
bool unscale();
size_t getNumRegs() const;
Type *getType() const;
void deleteBaseReg(const SCEV *&S);
bool referencesReg(const SCEV *S) const;
bool hasRegsUsedByUsesOtherThan(size_t LUIdx,
const RegUseTracker &RegUses) const;
void print(raw_ostream &OS) const;
void dump() const;
};
}
/// Recursion helper for initialMatch.
static void DoInitialMatch(const SCEV *S, Loop *L,
SmallVectorImpl<const SCEV *> &Good,
SmallVectorImpl<const SCEV *> &Bad,
ScalarEvolution &SE) {
// Collect expressions which properly dominate the loop header.
if (SE.properlyDominates(S, L->getHeader())) {
Good.push_back(S);
return;
}
// Look at add operands.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (const SCEV *S : Add->operands())
DoInitialMatch(S, L, Good, Bad, SE);
return;
}
// Look at addrec operands.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
if (!AR->getStart()->isZero()) {
DoInitialMatch(AR->getStart(), L, Good, Bad, SE);
DoInitialMatch(SE.getAddRecExpr(SE.getConstant(AR->getType(), 0),
AR->getStepRecurrence(SE),
// FIXME: AR->getNoWrapFlags()
AR->getLoop(), SCEV::FlagAnyWrap),
L, Good, Bad, SE);
return;
}
// Handle a multiplication by -1 (negation) if it didn't fold.
if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S))
if (Mul->getOperand(0)->isAllOnesValue()) {
SmallVector<const SCEV *, 4> Ops(Mul->op_begin()+1, Mul->op_end());
const SCEV *NewMul = SE.getMulExpr(Ops);
SmallVector<const SCEV *, 4> MyGood;
SmallVector<const SCEV *, 4> MyBad;
DoInitialMatch(NewMul, L, MyGood, MyBad, SE);
const SCEV *NegOne = SE.getSCEV(ConstantInt::getAllOnesValue(
SE.getEffectiveSCEVType(NewMul->getType())));
for (const SCEV *S : MyGood)
Good.push_back(SE.getMulExpr(NegOne, S));
for (const SCEV *S : MyBad)
Bad.push_back(SE.getMulExpr(NegOne, S));
return;
}
// Ok, we can't do anything interesting. Just stuff the whole thing into a
// register and hope for the best.
Bad.push_back(S);
}
/// Incorporate loop-variant parts of S into this Formula, attempting to keep
/// all loop-invariant and loop-computable values in a single base register.
void Formula::initialMatch(const SCEV *S, Loop *L, ScalarEvolution &SE) {
SmallVector<const SCEV *, 4> Good;
SmallVector<const SCEV *, 4> Bad;
DoInitialMatch(S, L, Good, Bad, SE);
if (!Good.empty()) {
const SCEV *Sum = SE.getAddExpr(Good);
if (!Sum->isZero())
BaseRegs.push_back(Sum);
HasBaseReg = true;
}
if (!Bad.empty()) {
const SCEV *Sum = SE.getAddExpr(Bad);
if (!Sum->isZero())
BaseRegs.push_back(Sum);
HasBaseReg = true;
}
canonicalize();
}
/// \brief Check whether or not this formula statisfies the canonical
/// representation.
/// \see Formula::BaseRegs.
bool Formula::isCanonical() const {
if (ScaledReg)
return Scale != 1 || !BaseRegs.empty();
return BaseRegs.size() <= 1;
}
/// \brief Helper method to morph a formula into its canonical representation.
/// \see Formula::BaseRegs.
/// Every formula having more than one base register, must use the ScaledReg
/// field. Otherwise, we would have to do special cases everywhere in LSR
/// to treat reg1 + reg2 + ... the same way as reg1 + 1*reg2 + ...
/// On the other hand, 1*reg should be canonicalized into reg.
void Formula::canonicalize() {
if (isCanonical())
return;
// So far we did not need this case. This is easy to implement but it is
// useless to maintain dead code. Beside it could hurt compile time.
assert(!BaseRegs.empty() && "1*reg => reg, should not be needed.");
// Keep the invariant sum in BaseRegs and one of the variant sum in ScaledReg.
ScaledReg = BaseRegs.back();
BaseRegs.pop_back();
Scale = 1;
size_t BaseRegsSize = BaseRegs.size();
size_t Try = 0;
// If ScaledReg is an invariant, try to find a variant expression.
while (Try < BaseRegsSize && !isa<SCEVAddRecExpr>(ScaledReg))
std::swap(ScaledReg, BaseRegs[Try++]);
}
/// \brief Get rid of the scale in the formula.
/// In other words, this method morphes reg1 + 1*reg2 into reg1 + reg2.
/// \return true if it was possible to get rid of the scale, false otherwise.
/// \note After this operation the formula may not be in the canonical form.
bool Formula::unscale() {
if (Scale != 1)
return false;
Scale = 0;
BaseRegs.push_back(ScaledReg);
ScaledReg = nullptr;
return true;
}
/// Return the total number of register operands used by this formula. This does
/// not include register uses implied by non-constant addrec strides.
size_t Formula::getNumRegs() const {
return !!ScaledReg + BaseRegs.size();
}
/// Return the type of this formula, if it has one, or null otherwise. This type
/// is meaningless except for the bit size.
Type *Formula::getType() const {
return !BaseRegs.empty() ? BaseRegs.front()->getType() :
ScaledReg ? ScaledReg->getType() :
BaseGV ? BaseGV->getType() :
nullptr;
}
/// Delete the given base reg from the BaseRegs list.
void Formula::deleteBaseReg(const SCEV *&S) {
if (&S != &BaseRegs.back())
std::swap(S, BaseRegs.back());
BaseRegs.pop_back();
}
/// Test if this formula references the given register.
bool Formula::referencesReg(const SCEV *S) const {
return S == ScaledReg || is_contained(BaseRegs, S);
}
/// Test whether this formula uses registers which are used by uses other than
/// the use with the given index.
bool Formula::hasRegsUsedByUsesOtherThan(size_t LUIdx,
const RegUseTracker &RegUses) const {
if (ScaledReg)
if (RegUses.isRegUsedByUsesOtherThan(ScaledReg, LUIdx))
return true;
for (const SCEV *BaseReg : BaseRegs)
if (RegUses.isRegUsedByUsesOtherThan(BaseReg, LUIdx))
return true;
return false;
}
void Formula::print(raw_ostream &OS) const {
bool First = true;
if (BaseGV) {
if (!First) OS << " + "; else First = false;
BaseGV->printAsOperand(OS, /*PrintType=*/false);
}
if (BaseOffset != 0) {
if (!First) OS << " + "; else First = false;
OS << BaseOffset;
}
for (const SCEV *BaseReg : BaseRegs) {
if (!First) OS << " + "; else First = false;
OS << "reg(" << *BaseReg << ')';
}
if (HasBaseReg && BaseRegs.empty()) {
if (!First) OS << " + "; else First = false;
OS << "**error: HasBaseReg**";
} else if (!HasBaseReg && !BaseRegs.empty()) {
if (!First) OS << " + "; else First = false;
OS << "**error: !HasBaseReg**";
}
if (Scale != 0) {
if (!First) OS << " + "; else First = false;
OS << Scale << "*reg(";
if (ScaledReg)
OS << *ScaledReg;
else
OS << "<unknown>";
OS << ')';
}
if (UnfoldedOffset != 0) {
if (!First) OS << " + ";
OS << "imm(" << UnfoldedOffset << ')';
}
}
LLVM_DUMP_METHOD
void Formula::dump() const {
print(errs()); errs() << '\n';
}
/// Return true if the given addrec can be sign-extended without changing its
/// value.
static bool isAddRecSExtable(const SCEVAddRecExpr *AR, ScalarEvolution &SE) {
Type *WideTy =
IntegerType::get(SE.getContext(), SE.getTypeSizeInBits(AR->getType()) + 1);
return isa<SCEVAddRecExpr>(SE.getSignExtendExpr(AR, WideTy));
}
/// Return true if the given add can be sign-extended without changing its
/// value.
static bool isAddSExtable(const SCEVAddExpr *A, ScalarEvolution &SE) {
Type *WideTy =
IntegerType::get(SE.getContext(), SE.getTypeSizeInBits(A->getType()) + 1);
return isa<SCEVAddExpr>(SE.getSignExtendExpr(A, WideTy));
}
/// Return true if the given mul can be sign-extended without changing its
/// value.
static bool isMulSExtable(const SCEVMulExpr *M, ScalarEvolution &SE) {
Type *WideTy =
IntegerType::get(SE.getContext(),
SE.getTypeSizeInBits(M->getType()) * M->getNumOperands());
return isa<SCEVMulExpr>(SE.getSignExtendExpr(M, WideTy));
}
/// Return an expression for LHS /s RHS, if it can be determined and if the
/// remainder is known to be zero, or null otherwise. If IgnoreSignificantBits
/// is true, expressions like (X * Y) /s Y are simplified to Y, ignoring that
/// the multiplication may overflow, which is useful when the result will be
/// used in a context where the most significant bits are ignored.
static const SCEV *getExactSDiv(const SCEV *LHS, const SCEV *RHS,
ScalarEvolution &SE,
bool IgnoreSignificantBits = false) {
// Handle the trivial case, which works for any SCEV type.
if (LHS == RHS)
return SE.getConstant(LHS->getType(), 1);
// Handle a few RHS special cases.
const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS);
if (RC) {
const APInt &RA = RC->getAPInt();
// Handle x /s -1 as x * -1, to give ScalarEvolution a chance to do
// some folding.
if (RA.isAllOnesValue())
return SE.getMulExpr(LHS, RC);
// Handle x /s 1 as x.
if (RA == 1)
return LHS;
}
// Check for a division of a constant by a constant.
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(LHS)) {
if (!RC)
return nullptr;
const APInt &LA = C->getAPInt();
const APInt &RA = RC->getAPInt();
if (LA.srem(RA) != 0)
return nullptr;
return SE.getConstant(LA.sdiv(RA));
}
// Distribute the sdiv over addrec operands, if the addrec doesn't overflow.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) {
if (IgnoreSignificantBits || isAddRecSExtable(AR, SE)) {
const SCEV *Step = getExactSDiv(AR->getStepRecurrence(SE), RHS, SE,
IgnoreSignificantBits);
if (!Step) return nullptr;
const SCEV *Start = getExactSDiv(AR->getStart(), RHS, SE,
IgnoreSignificantBits);
if (!Start) return nullptr;
// FlagNW is independent of the start value, step direction, and is
// preserved with smaller magnitude steps.
// FIXME: AR->getNoWrapFlags(SCEV::FlagNW)
return SE.getAddRecExpr(Start, Step, AR->getLoop(), SCEV::FlagAnyWrap);
}
return nullptr;
}
// Distribute the sdiv over add operands, if the add doesn't overflow.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(LHS)) {
if (IgnoreSignificantBits || isAddSExtable(Add, SE)) {
SmallVector<const SCEV *, 8> Ops;
for (const SCEV *S : Add->operands()) {
const SCEV *Op = getExactSDiv(S, RHS, SE, IgnoreSignificantBits);
if (!Op) return nullptr;
Ops.push_back(Op);
}
return SE.getAddExpr(Ops);
}
return nullptr;
}
// Check for a multiply operand that we can pull RHS out of.
if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(LHS)) {
if (IgnoreSignificantBits || isMulSExtable(Mul, SE)) {
SmallVector<const SCEV *, 4> Ops;
bool Found = false;
for (const SCEV *S : Mul->operands()) {
if (!Found)
if (const SCEV *Q = getExactSDiv(S, RHS, SE,
IgnoreSignificantBits)) {
S = Q;
Found = true;
}
Ops.push_back(S);
}
return Found ? SE.getMulExpr(Ops) : nullptr;
}
return nullptr;
}
// Otherwise we don't know.
return nullptr;
}
/// If S involves the addition of a constant integer value, return that integer
/// value, and mutate S to point to a new SCEV with that value excluded.
static int64_t ExtractImmediate(const SCEV *&S, ScalarEvolution &SE) {
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) {
if (C->getAPInt().getMinSignedBits() <= 64) {
S = SE.getConstant(C->getType(), 0);
return C->getValue()->getSExtValue();
}
} else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end());
int64_t Result = ExtractImmediate(NewOps.front(), SE);
if (Result != 0)
S = SE.getAddExpr(NewOps);
return Result;
} else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end());
int64_t Result = ExtractImmediate(NewOps.front(), SE);
if (Result != 0)
S = SE.getAddRecExpr(NewOps, AR->getLoop(),
// FIXME: AR->getNoWrapFlags(SCEV::FlagNW)
SCEV::FlagAnyWrap);
return Result;
}
return 0;
}
/// If S involves the addition of a GlobalValue address, return that symbol, and
/// mutate S to point to a new SCEV with that value excluded.
static GlobalValue *ExtractSymbol(const SCEV *&S, ScalarEvolution &SE) {
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(U->getValue())) {
S = SE.getConstant(GV->getType(), 0);
return GV;
}
} else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
SmallVector<const SCEV *, 8> NewOps(Add->op_begin(), Add->op_end());
GlobalValue *Result = ExtractSymbol(NewOps.back(), SE);
if (Result)
S = SE.getAddExpr(NewOps);
return Result;
} else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
SmallVector<const SCEV *, 8> NewOps(AR->op_begin(), AR->op_end());
GlobalValue *Result = ExtractSymbol(NewOps.front(), SE);
if (Result)
S = SE.getAddRecExpr(NewOps, AR->getLoop(),
// FIXME: AR->getNoWrapFlags(SCEV::FlagNW)
SCEV::FlagAnyWrap);
return Result;
}
return nullptr;
}
/// Returns true if the specified instruction is using the specified value as an
/// address.
static bool isAddressUse(Instruction *Inst, Value *OperandVal) {
bool isAddress = isa<LoadInst>(Inst);
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (SI->getOperand(1) == OperandVal)
isAddress = true;
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
// Addressing modes can also be folded into prefetches and a variety
// of intrinsics.
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::prefetch:
if (II->getArgOperand(0) == OperandVal)
isAddress = true;
break;
}
}
return isAddress;
}
/// Return the type of the memory being accessed.
static MemAccessTy getAccessType(const Instruction *Inst) {
MemAccessTy AccessTy(Inst->getType(), MemAccessTy::UnknownAddressSpace);
if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
AccessTy.MemTy = SI->getOperand(0)->getType();
AccessTy.AddrSpace = SI->getPointerAddressSpace();
} else if (const LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
AccessTy.AddrSpace = LI->getPointerAddressSpace();
}
// All pointers have the same requirements, so canonicalize them to an
// arbitrary pointer type to minimize variation.
if (PointerType *PTy = dyn_cast<PointerType>(AccessTy.MemTy))
AccessTy.MemTy = PointerType::get(IntegerType::get(PTy->getContext(), 1),
PTy->getAddressSpace());
return AccessTy;
}
/// Return true if this AddRec is already a phi in its loop.
static bool isExistingPhi(const SCEVAddRecExpr *AR, ScalarEvolution &SE) {
for (BasicBlock::iterator I = AR->getLoop()->getHeader()->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
if (SE.isSCEVable(PN->getType()) &&
(SE.getEffectiveSCEVType(PN->getType()) ==
SE.getEffectiveSCEVType(AR->getType())) &&
SE.getSCEV(PN) == AR)
return true;
}
return false;
}
/// Check if expanding this expression is likely to incur significant cost. This
/// is tricky because SCEV doesn't track which expressions are actually computed
/// by the current IR.
///
/// We currently allow expansion of IV increments that involve adds,
/// multiplication by constants, and AddRecs from existing phis.
///
/// TODO: Allow UDivExpr if we can find an existing IV increment that is an
/// obvious multiple of the UDivExpr.
static bool isHighCostExpansion(const SCEV *S,
SmallPtrSetImpl<const SCEV*> &Processed,
ScalarEvolution &SE) {
// Zero/One operand expressions
switch (S->getSCEVType()) {
case scUnknown:
case scConstant:
return false;
case scTruncate:
return isHighCostExpansion(cast<SCEVTruncateExpr>(S)->getOperand(),
Processed, SE);
case scZeroExtend:
return isHighCostExpansion(cast<SCEVZeroExtendExpr>(S)->getOperand(),
Processed, SE);
case scSignExtend:
return isHighCostExpansion(cast<SCEVSignExtendExpr>(S)->getOperand(),
Processed, SE);
}
if (!Processed.insert(S).second)
return false;
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
for (const SCEV *S : Add->operands()) {
if (isHighCostExpansion(S, Processed, SE))
return true;
}
return false;
}
if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
if (Mul->getNumOperands() == 2) {
// Multiplication by a constant is ok
if (isa<SCEVConstant>(Mul->getOperand(0)))
return isHighCostExpansion(Mul->getOperand(1), Processed, SE);
// If we have the value of one operand, check if an existing
// multiplication already generates this expression.
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(Mul->getOperand(1))) {
Value *UVal = U->getValue();
for (User *UR : UVal->users()) {
// If U is a constant, it may be used by a ConstantExpr.
Instruction *UI = dyn_cast<Instruction>(UR);
if (UI && UI->getOpcode() == Instruction::Mul &&
SE.isSCEVable(UI->getType())) {
return SE.getSCEV(UI) == Mul;
}
}
}
}
}
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
if (isExistingPhi(AR, SE))
return false;
}
// Fow now, consider any other type of expression (div/mul/min/max) high cost.
return true;
}
/// If any of the instructions is the specified set are trivially dead, delete
/// them and see if this makes any of their operands subsequently dead.
static bool
DeleteTriviallyDeadInstructions(SmallVectorImpl<WeakVH> &DeadInsts) {
bool Changed = false;
while (!DeadInsts.empty()) {
Value *V = DeadInsts.pop_back_val();
Instruction *I = dyn_cast_or_null<Instruction>(V);
if (!I || !isInstructionTriviallyDead(I))
continue;
for (Use &O : I->operands())
if (Instruction *U = dyn_cast<Instruction>(O)) {
O = nullptr;
if (U->use_empty())
DeadInsts.emplace_back(U);
}
I->eraseFromParent();
Changed = true;
}
return Changed;
}
namespace {
class LSRUse;
}
/// \brief Check if the addressing mode defined by \p F is completely
/// folded in \p LU at isel time.
/// This includes address-mode folding and special icmp tricks.
/// This function returns true if \p LU can accommodate what \p F
/// defines and up to 1 base + 1 scaled + offset.
/// In other words, if \p F has several base registers, this function may
/// still return true. Therefore, users still need to account for
/// additional base registers and/or unfolded offsets to derive an
/// accurate cost model.
static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
const LSRUse &LU, const Formula &F);
// Get the cost of the scaling factor used in F for LU.
static unsigned getScalingFactorCost(const TargetTransformInfo &TTI,
const LSRUse &LU, const Formula &F);
namespace {
/// This class is used to measure and compare candidate formulae.
class Cost {
/// TODO: Some of these could be merged. Also, a lexical ordering
/// isn't always optimal.
unsigned NumRegs;
unsigned AddRecCost;
unsigned NumIVMuls;
unsigned NumBaseAdds;
unsigned ImmCost;
unsigned SetupCost;
unsigned ScaleCost;
public:
Cost()
: NumRegs(0), AddRecCost(0), NumIVMuls(0), NumBaseAdds(0), ImmCost(0),
SetupCost(0), ScaleCost(0) {}
bool operator<(const Cost &Other) const;
void Lose();
#ifndef NDEBUG
// Once any of the metrics loses, they must all remain losers.
bool isValid() {
return ((NumRegs | AddRecCost | NumIVMuls | NumBaseAdds
| ImmCost | SetupCost | ScaleCost) != ~0u)
|| ((NumRegs & AddRecCost & NumIVMuls & NumBaseAdds
& ImmCost & SetupCost & ScaleCost) == ~0u);
}
#endif
bool isLoser() {
assert(isValid() && "invalid cost");
return NumRegs == ~0u;
}
void RateFormula(const TargetTransformInfo &TTI,
const Formula &F,
SmallPtrSetImpl<const SCEV *> &Regs,
const DenseSet<const SCEV *> &VisitedRegs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT,
const LSRUse &LU,
SmallPtrSetImpl<const SCEV *> *LoserRegs = nullptr);
void print(raw_ostream &OS) const;
void dump() const;
private:
void RateRegister(const SCEV *Reg,
SmallPtrSetImpl<const SCEV *> &Regs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT);
void RatePrimaryRegister(const SCEV *Reg,
SmallPtrSetImpl<const SCEV *> &Regs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT,
SmallPtrSetImpl<const SCEV *> *LoserRegs);
};
/// An operand value in an instruction which is to be replaced with some
/// equivalent, possibly strength-reduced, replacement.
struct LSRFixup {
/// The instruction which will be updated.
Instruction *UserInst;
/// The operand of the instruction which will be replaced. The operand may be
/// used more than once; every instance will be replaced.
Value *OperandValToReplace;
/// If this user is to use the post-incremented value of an induction
/// variable, this variable is non-null and holds the loop associated with the
/// induction variable.
PostIncLoopSet PostIncLoops;
/// A constant offset to be added to the LSRUse expression. This allows
/// multiple fixups to share the same LSRUse with different offsets, for
/// example in an unrolled loop.
int64_t Offset;
bool isUseFullyOutsideLoop(const Loop *L) const;
LSRFixup();
void print(raw_ostream &OS) const;
void dump() const;
};
/// A DenseMapInfo implementation for holding DenseMaps and DenseSets of sorted
/// SmallVectors of const SCEV*.
struct UniquifierDenseMapInfo {
static SmallVector<const SCEV *, 4> getEmptyKey() {
SmallVector<const SCEV *, 4> V;
V.push_back(reinterpret_cast<const SCEV *>(-1));
return V;
}
static SmallVector<const SCEV *, 4> getTombstoneKey() {
SmallVector<const SCEV *, 4> V;
V.push_back(reinterpret_cast<const SCEV *>(-2));
return V;
}
static unsigned getHashValue(const SmallVector<const SCEV *, 4> &V) {
return static_cast<unsigned>(hash_combine_range(V.begin(), V.end()));
}
static bool isEqual(const SmallVector<const SCEV *, 4> &LHS,
const SmallVector<const SCEV *, 4> &RHS) {
return LHS == RHS;
}
};
/// This class holds the state that LSR keeps for each use in IVUsers, as well
/// as uses invented by LSR itself. It includes information about what kinds of
/// things can be folded into the user, information about the user itself, and
/// information about how the use may be satisfied. TODO: Represent multiple
/// users of the same expression in common?
class LSRUse {
DenseSet<SmallVector<const SCEV *, 4>, UniquifierDenseMapInfo> Uniquifier;
public:
/// An enum for a kind of use, indicating what types of scaled and immediate
/// operands it might support.
enum KindType {
Basic, ///< A normal use, with no folding.
Special, ///< A special case of basic, allowing -1 scales.
Address, ///< An address use; folding according to TargetLowering
ICmpZero ///< An equality icmp with both operands folded into one.
// TODO: Add a generic icmp too?
};
typedef PointerIntPair<const SCEV *, 2, KindType> SCEVUseKindPair;
KindType Kind;
MemAccessTy AccessTy;
/// The list of operands which are to be replaced.
SmallVector<LSRFixup, 8> Fixups;
/// Keep track of the min and max offsets of the fixups.
int64_t MinOffset;
int64_t MaxOffset;
/// This records whether all of the fixups using this LSRUse are outside of
/// the loop, in which case some special-case heuristics may be used.
bool AllFixupsOutsideLoop;
/// RigidFormula is set to true to guarantee that this use will be associated
/// with a single formula--the one that initially matched. Some SCEV
/// expressions cannot be expanded. This allows LSR to consider the registers
/// used by those expressions without the need to expand them later after
/// changing the formula.
bool RigidFormula;
/// This records the widest use type for any fixup using this
/// LSRUse. FindUseWithSimilarFormula can't consider uses with different max
/// fixup widths to be equivalent, because the narrower one may be relying on
/// the implicit truncation to truncate away bogus bits.
Type *WidestFixupType;
/// A list of ways to build a value that can satisfy this user. After the
/// list is populated, one of these is selected heuristically and used to
/// formulate a replacement for OperandValToReplace in UserInst.
SmallVector<Formula, 12> Formulae;
/// The set of register candidates used by all formulae in this LSRUse.
SmallPtrSet<const SCEV *, 4> Regs;
LSRUse(KindType K, MemAccessTy AT)
: Kind(K), AccessTy(AT), MinOffset(INT64_MAX), MaxOffset(INT64_MIN),
AllFixupsOutsideLoop(true), RigidFormula(false),
WidestFixupType(nullptr) {}
LSRFixup &getNewFixup() {
Fixups.push_back(LSRFixup());
return Fixups.back();
}
void pushFixup(LSRFixup &f) {
Fixups.push_back(f);
if (f.Offset > MaxOffset)
MaxOffset = f.Offset;
if (f.Offset < MinOffset)
MinOffset = f.Offset;
}
bool HasFormulaWithSameRegs(const Formula &F) const;
bool InsertFormula(const Formula &F);
void DeleteFormula(Formula &F);
void RecomputeRegs(size_t LUIdx, RegUseTracker &Reguses);
void print(raw_ostream &OS) const;
void dump() const;
};
}
/// Tally up interesting quantities from the given register.
void Cost::RateRegister(const SCEV *Reg,
SmallPtrSetImpl<const SCEV *> &Regs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT) {
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Reg)) {
// If this is an addrec for another loop, don't second-guess its addrec phi
// nodes. LSR isn't currently smart enough to reason about more than one
// loop at a time. LSR has already run on inner loops, will not run on outer
// loops, and cannot be expected to change sibling loops.
if (AR->getLoop() != L) {
// If the AddRec exists, consider it's register free and leave it alone.
if (isExistingPhi(AR, SE))
return;
// Otherwise, do not consider this formula at all.
Lose();
return;
}
AddRecCost += 1; /// TODO: This should be a function of the stride.
// Add the step value register, if it needs one.
// TODO: The non-affine case isn't precisely modeled here.
if (!AR->isAffine() || !isa<SCEVConstant>(AR->getOperand(1))) {
if (!Regs.count(AR->getOperand(1))) {
RateRegister(AR->getOperand(1), Regs, L, SE, DT);
if (isLoser())
return;
}
}
}
++NumRegs;
// Rough heuristic; favor registers which don't require extra setup
// instructions in the preheader.
if (!isa<SCEVUnknown>(Reg) &&
!isa<SCEVConstant>(Reg) &&
!(isa<SCEVAddRecExpr>(Reg) &&
(isa<SCEVUnknown>(cast<SCEVAddRecExpr>(Reg)->getStart()) ||
isa<SCEVConstant>(cast<SCEVAddRecExpr>(Reg)->getStart()))))
++SetupCost;
NumIVMuls += isa<SCEVMulExpr>(Reg) &&
SE.hasComputableLoopEvolution(Reg, L);
}
/// Record this register in the set. If we haven't seen it before, rate
/// it. Optional LoserRegs provides a way to declare any formula that refers to
/// one of those regs an instant loser.
void Cost::RatePrimaryRegister(const SCEV *Reg,
SmallPtrSetImpl<const SCEV *> &Regs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT,
SmallPtrSetImpl<const SCEV *> *LoserRegs) {
if (LoserRegs && LoserRegs->count(Reg)) {
Lose();
return;
}
if (Regs.insert(Reg).second) {
RateRegister(Reg, Regs, L, SE, DT);
if (LoserRegs && isLoser())
LoserRegs->insert(Reg);
}
}
void Cost::RateFormula(const TargetTransformInfo &TTI,
const Formula &F,
SmallPtrSetImpl<const SCEV *> &Regs,
const DenseSet<const SCEV *> &VisitedRegs,
const Loop *L,
ScalarEvolution &SE, DominatorTree &DT,
const LSRUse &LU,
SmallPtrSetImpl<const SCEV *> *LoserRegs) {
assert(F.isCanonical() && "Cost is accurate only for canonical formula");
// Tally up the registers.
if (const SCEV *ScaledReg = F.ScaledReg) {
if (VisitedRegs.count(ScaledReg)) {
Lose();
return;
}
RatePrimaryRegister(ScaledReg, Regs, L, SE, DT, LoserRegs);
if (isLoser())
return;
}
for (const SCEV *BaseReg : F.BaseRegs) {
if (VisitedRegs.count(BaseReg)) {
Lose();
return;
}
RatePrimaryRegister(BaseReg, Regs, L, SE, DT, LoserRegs);
if (isLoser())
return;
}
// Determine how many (unfolded) adds we'll need inside the loop.
size_t NumBaseParts = F.getNumRegs();
if (NumBaseParts > 1)
// Do not count the base and a possible second register if the target
// allows to fold 2 registers.
NumBaseAdds +=
NumBaseParts - (1 + (F.Scale && isAMCompletelyFolded(TTI, LU, F)));
NumBaseAdds += (F.UnfoldedOffset != 0);
// Accumulate non-free scaling amounts.
ScaleCost += getScalingFactorCost(TTI, LU, F);
// Tally up the non-zero immediates.
for (const LSRFixup &Fixup : LU.Fixups) {
int64_t O = Fixup.Offset;
int64_t Offset = (uint64_t)O + F.BaseOffset;
if (F.BaseGV)
ImmCost += 64; // Handle symbolic values conservatively.
// TODO: This should probably be the pointer size.
else if (Offset != 0)
ImmCost += APInt(64, Offset, true).getMinSignedBits();
// Check with target if this offset with this instruction is
// specifically not supported.
if ((isa<LoadInst>(Fixup.UserInst) || isa<StoreInst>(Fixup.UserInst)) &&
!TTI.isFoldableMemAccessOffset(Fixup.UserInst, Offset))
NumBaseAdds++;
}
assert(isValid() && "invalid cost");
}
/// Set this cost to a losing value.
void Cost::Lose() {
NumRegs = ~0u;
AddRecCost = ~0u;
NumIVMuls = ~0u;
NumBaseAdds = ~0u;
ImmCost = ~0u;
SetupCost = ~0u;
ScaleCost = ~0u;
}
/// Choose the lower cost.
bool Cost::operator<(const Cost &Other) const {
return std::tie(NumRegs, AddRecCost, NumIVMuls, NumBaseAdds, ScaleCost,
ImmCost, SetupCost) <
std::tie(Other.NumRegs, Other.AddRecCost, Other.NumIVMuls,
Other.NumBaseAdds, Other.ScaleCost, Other.ImmCost,
Other.SetupCost);
}
void Cost::print(raw_ostream &OS) const {
OS << NumRegs << " reg" << (NumRegs == 1 ? "" : "s");
if (AddRecCost != 0)
OS << ", with addrec cost " << AddRecCost;
if (NumIVMuls != 0)
OS << ", plus " << NumIVMuls << " IV mul" << (NumIVMuls == 1 ? "" : "s");
if (NumBaseAdds != 0)
OS << ", plus " << NumBaseAdds << " base add"
<< (NumBaseAdds == 1 ? "" : "s");
if (ScaleCost != 0)
OS << ", plus " << ScaleCost << " scale cost";
if (ImmCost != 0)
OS << ", plus " << ImmCost << " imm cost";
if (SetupCost != 0)
OS << ", plus " << SetupCost << " setup cost";
}
LLVM_DUMP_METHOD
void Cost::dump() const {
print(errs()); errs() << '\n';
}
LSRFixup::LSRFixup()
: UserInst(nullptr), OperandValToReplace(nullptr),
Offset(0) {}
/// Test whether this fixup always uses its value outside of the given loop.
bool LSRFixup::isUseFullyOutsideLoop(const Loop *L) const {
// PHI nodes use their value in their incoming blocks.
if (const PHINode *PN = dyn_cast<PHINode>(UserInst)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == OperandValToReplace &&
L->contains(PN->getIncomingBlock(i)))
return false;
return true;
}
return !L->contains(UserInst);
}
void LSRFixup::print(raw_ostream &OS) const {
OS << "UserInst=";
// Store is common and interesting enough to be worth special-casing.
if (StoreInst *Store = dyn_cast<StoreInst>(UserInst)) {
OS << "store ";
Store->getOperand(0)->printAsOperand(OS, /*PrintType=*/false);
} else if (UserInst->getType()->isVoidTy())
OS << UserInst->getOpcodeName();
else
UserInst->printAsOperand(OS, /*PrintType=*/false);
OS << ", OperandValToReplace=";
OperandValToReplace->printAsOperand(OS, /*PrintType=*/false);
for (const Loop *PIL : PostIncLoops) {
OS << ", PostIncLoop=";
PIL->getHeader()->printAsOperand(OS, /*PrintType=*/false);
}
if (Offset != 0)
OS << ", Offset=" << Offset;
}
LLVM_DUMP_METHOD
void LSRFixup::dump() const {
print(errs()); errs() << '\n';
}
/// Test whether this use as a formula which has the same registers as the given
/// formula.
bool LSRUse::HasFormulaWithSameRegs(const Formula &F) const {
SmallVector<const SCEV *, 4> Key = F.BaseRegs;
if (F.ScaledReg) Key.push_back(F.ScaledReg);
// Unstable sort by host order ok, because this is only used for uniquifying.
std::sort(Key.begin(), Key.end());
return Uniquifier.count(Key);
}
/// If the given formula has not yet been inserted, add it to the list, and
/// return true. Return false otherwise. The formula must be in canonical form.
bool LSRUse::InsertFormula(const Formula &F) {
assert(F.isCanonical() && "Invalid canonical representation");
if (!Formulae.empty() && RigidFormula)
return false;
SmallVector<const SCEV *, 4> Key = F.BaseRegs;
if (F.ScaledReg) Key.push_back(F.ScaledReg);
// Unstable sort by host order ok, because this is only used for uniquifying.
std::sort(Key.begin(), Key.end());
if (!Uniquifier.insert(Key).second)
return false;
// Using a register to hold the value of 0 is not profitable.
assert((!F.ScaledReg || !F.ScaledReg->isZero()) &&
"Zero allocated in a scaled register!");
#ifndef NDEBUG
for (const SCEV *BaseReg : F.BaseRegs)
assert(!BaseReg->isZero() && "Zero allocated in a base register!");
#endif
// Add the formula to the list.
Formulae.push_back(F);
// Record registers now being used by this use.
Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
if (F.ScaledReg)
Regs.insert(F.ScaledReg);
return true;
}
/// Remove the given formula from this use's list.
void LSRUse::DeleteFormula(Formula &F) {
if (&F != &Formulae.back())
std::swap(F, Formulae.back());
Formulae.pop_back();
}
/// Recompute the Regs field, and update RegUses.
void LSRUse::RecomputeRegs(size_t LUIdx, RegUseTracker &RegUses) {
// Now that we've filtered out some formulae, recompute the Regs set.
SmallPtrSet<const SCEV *, 4> OldRegs = std::move(Regs);
Regs.clear();
for (const Formula &F : Formulae) {
if (F.ScaledReg) Regs.insert(F.ScaledReg);
Regs.insert(F.BaseRegs.begin(), F.BaseRegs.end());
}
// Update the RegTracker.
for (const SCEV *S : OldRegs)
if (!Regs.count(S))
RegUses.dropRegister(S, LUIdx);
}
void LSRUse::print(raw_ostream &OS) const {
OS << "LSR Use: Kind=";
switch (Kind) {
case Basic: OS << "Basic"; break;
case Special: OS << "Special"; break;
case ICmpZero: OS << "ICmpZero"; break;
case Address:
OS << "Address of ";
if (AccessTy.MemTy->isPointerTy())
OS << "pointer"; // the full pointer type could be really verbose
else {
OS << *AccessTy.MemTy;
}
OS << " in addrspace(" << AccessTy.AddrSpace << ')';
}
OS << ", Offsets={";
bool NeedComma = false;
for (const LSRFixup &Fixup : Fixups) {
if (NeedComma) OS << ',';
OS << Fixup.Offset;
NeedComma = true;
}
OS << '}';
if (AllFixupsOutsideLoop)
OS << ", all-fixups-outside-loop";
if (WidestFixupType)
OS << ", widest fixup type: " << *WidestFixupType;
}
LLVM_DUMP_METHOD
void LSRUse::dump() const {
print(errs()); errs() << '\n';
}
static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
LSRUse::KindType Kind, MemAccessTy AccessTy,
GlobalValue *BaseGV, int64_t BaseOffset,
bool HasBaseReg, int64_t Scale) {
switch (Kind) {
case LSRUse::Address:
return TTI.isLegalAddressingMode(AccessTy.MemTy, BaseGV, BaseOffset,
HasBaseReg, Scale, AccessTy.AddrSpace);
case LSRUse::ICmpZero:
// There's not even a target hook for querying whether it would be legal to
// fold a GV into an ICmp.
if (BaseGV)
return false;
// ICmp only has two operands; don't allow more than two non-trivial parts.
if (Scale != 0 && HasBaseReg && BaseOffset != 0)
return false;
// ICmp only supports no scale or a -1 scale, as we can "fold" a -1 scale by
// putting the scaled register in the other operand of the icmp.
if (Scale != 0 && Scale != -1)
return false;
// If we have low-level target information, ask the target if it can fold an
// integer immediate on an icmp.
if (BaseOffset != 0) {
// We have one of:
// ICmpZero BaseReg + BaseOffset => ICmp BaseReg, -BaseOffset
// ICmpZero -1*ScaleReg + BaseOffset => ICmp ScaleReg, BaseOffset
// Offs is the ICmp immediate.
if (Scale == 0)
// The cast does the right thing with INT64_MIN.
BaseOffset = -(uint64_t)BaseOffset;
return TTI.isLegalICmpImmediate(BaseOffset);
}
// ICmpZero BaseReg + -1*ScaleReg => ICmp BaseReg, ScaleReg
return true;
case LSRUse::Basic:
// Only handle single-register values.
return !BaseGV && Scale == 0 && BaseOffset == 0;
case LSRUse::Special:
// Special case Basic to handle -1 scales.
return !BaseGV && (Scale == 0 || Scale == -1) && BaseOffset == 0;
}
llvm_unreachable("Invalid LSRUse Kind!");
}
static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
int64_t MinOffset, int64_t MaxOffset,
LSRUse::KindType Kind, MemAccessTy AccessTy,
GlobalValue *BaseGV, int64_t BaseOffset,
bool HasBaseReg, int64_t Scale) {
// Check for overflow.
if (((int64_t)((uint64_t)BaseOffset + MinOffset) > BaseOffset) !=
(MinOffset > 0))
return false;
MinOffset = (uint64_t)BaseOffset + MinOffset;
if (((int64_t)((uint64_t)BaseOffset + MaxOffset) > BaseOffset) !=
(MaxOffset > 0))
return false;
MaxOffset = (uint64_t)BaseOffset + MaxOffset;
return isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, MinOffset,
HasBaseReg, Scale) &&
isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, MaxOffset,
HasBaseReg, Scale);
}
static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
int64_t MinOffset, int64_t MaxOffset,
LSRUse::KindType Kind, MemAccessTy AccessTy,
const Formula &F) {
// For the purpose of isAMCompletelyFolded either having a canonical formula
// or a scale not equal to zero is correct.
// Problems may arise from non canonical formulae having a scale == 0.
// Strictly speaking it would best to just rely on canonical formulae.
// However, when we generate the scaled formulae, we first check that the
// scaling factor is profitable before computing the actual ScaledReg for
// compile time sake.
assert((F.isCanonical() || F.Scale != 0));
return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy,
F.BaseGV, F.BaseOffset, F.HasBaseReg, F.Scale);
}
/// Test whether we know how to expand the current formula.
static bool isLegalUse(const TargetTransformInfo &TTI, int64_t MinOffset,
int64_t MaxOffset, LSRUse::KindType Kind,
MemAccessTy AccessTy, GlobalValue *BaseGV,
int64_t BaseOffset, bool HasBaseReg, int64_t Scale) {
// We know how to expand completely foldable formulae.
return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, BaseGV,
BaseOffset, HasBaseReg, Scale) ||
// Or formulae that use a base register produced by a sum of base
// registers.
(Scale == 1 &&
isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy,
BaseGV, BaseOffset, true, 0));
}
static bool isLegalUse(const TargetTransformInfo &TTI, int64_t MinOffset,
int64_t MaxOffset, LSRUse::KindType Kind,
MemAccessTy AccessTy, const Formula &F) {
return isLegalUse(TTI, MinOffset, MaxOffset, Kind, AccessTy, F.BaseGV,
F.BaseOffset, F.HasBaseReg, F.Scale);
}
static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
const LSRUse &LU, const Formula &F) {
return isAMCompletelyFolded(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind,
LU.AccessTy, F.BaseGV, F.BaseOffset, F.HasBaseReg,
F.Scale);
}
static unsigned getScalingFactorCost(const TargetTransformInfo &TTI,
const LSRUse &LU, const Formula &F) {
if (!F.Scale)
return 0;
// If the use is not completely folded in that instruction, we will have to
// pay an extra cost only for scale != 1.
if (!isAMCompletelyFolded(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind,
LU.AccessTy, F))
return F.Scale != 1;
switch (LU.Kind) {
case LSRUse::Address: {
// Check the scaling factor cost with both the min and max offsets.
int ScaleCostMinOffset = TTI.getScalingFactorCost(
LU.AccessTy.MemTy, F.BaseGV, F.BaseOffset + LU.MinOffset, F.HasBaseReg,
F.Scale, LU.AccessTy.AddrSpace);
int ScaleCostMaxOffset = TTI.getScalingFactorCost(
LU.AccessTy.MemTy, F.BaseGV, F.BaseOffset + LU.MaxOffset, F.HasBaseReg,
F.Scale, LU.AccessTy.AddrSpace);
assert(ScaleCostMinOffset >= 0 && ScaleCostMaxOffset >= 0 &&
"Legal addressing mode has an illegal cost!");
return std::max(ScaleCostMinOffset, ScaleCostMaxOffset);
}
case LSRUse::ICmpZero:
case LSRUse::Basic:
case LSRUse::Special:
// The use is completely folded, i.e., everything is folded into the
// instruction.
return 0;
}
llvm_unreachable("Invalid LSRUse Kind!");
}
static bool isAlwaysFoldable(const TargetTransformInfo &TTI,
LSRUse::KindType Kind, MemAccessTy AccessTy,
GlobalValue *BaseGV, int64_t BaseOffset,
bool HasBaseReg) {
// Fast-path: zero is always foldable.
if (BaseOffset == 0 && !BaseGV) return true;
// Conservatively, create an address with an immediate and a
// base and a scale.
int64_t Scale = Kind == LSRUse::ICmpZero ? -1 : 1;
// Canonicalize a scale of 1 to a base register if the formula doesn't
// already have a base register.
if (!HasBaseReg && Scale == 1) {
Scale = 0;
HasBaseReg = true;
}
return isAMCompletelyFolded(TTI, Kind, AccessTy, BaseGV, BaseOffset,
HasBaseReg, Scale);
}
static bool isAlwaysFoldable(const TargetTransformInfo &TTI,
ScalarEvolution &SE, int64_t MinOffset,
int64_t MaxOffset, LSRUse::KindType Kind,
MemAccessTy AccessTy, const SCEV *S,
bool HasBaseReg) {
// Fast-path: zero is always foldable.
if (S->isZero()) return true;
// Conservatively, create an address with an immediate and a
// base and a scale.
int64_t BaseOffset = ExtractImmediate(S, SE);
GlobalValue *BaseGV = ExtractSymbol(S, SE);
// If there's anything else involved, it's not foldable.
if (!S->isZero()) return false;
// Fast-path: zero is always foldable.
if (BaseOffset == 0 && !BaseGV) return true;
// Conservatively, create an address with an immediate and a
// base and a scale.
int64_t Scale = Kind == LSRUse::ICmpZero ? -1 : 1;
return isAMCompletelyFolded(TTI, MinOffset, MaxOffset, Kind, AccessTy, BaseGV,
BaseOffset, HasBaseReg, Scale);
}
namespace {
/// An individual increment in a Chain of IV increments. Relate an IV user to
/// an expression that computes the IV it uses from the IV used by the previous
/// link in the Chain.
///
/// For the head of a chain, IncExpr holds the absolute SCEV expression for the
/// original IVOperand. The head of the chain's IVOperand is only valid during
/// chain collection, before LSR replaces IV users. During chain generation,
/// IncExpr can be used to find the new IVOperand that computes the same
/// expression.
struct IVInc {
Instruction *UserInst;
Value* IVOperand;
const SCEV *IncExpr;
IVInc(Instruction *U, Value *O, const SCEV *E):
UserInst(U), IVOperand(O), IncExpr(E) {}
};
// The list of IV increments in program order. We typically add the head of a
// chain without finding subsequent links.
struct IVChain {
SmallVector<IVInc,1> Incs;
const SCEV *ExprBase;
IVChain() : ExprBase(nullptr) {}
IVChain(const IVInc &Head, const SCEV *Base)
: Incs(1, Head), ExprBase(Base) {}
typedef SmallVectorImpl<IVInc>::const_iterator const_iterator;
// Return the first increment in the chain.
const_iterator begin() const {
assert(!Incs.empty());
return std::next(Incs.begin());
}
const_iterator end() const {
return Incs.end();
}
// Returns true if this chain contains any increments.
bool hasIncs() const { return Incs.size() >= 2; }
// Add an IVInc to the end of this chain.
void add(const IVInc &X) { Incs.push_back(X); }
// Returns the last UserInst in the chain.
Instruction *tailUserInst() const { return Incs.back().UserInst; }
// Returns true if IncExpr can be profitably added to this chain.
bool isProfitableIncrement(const SCEV *OperExpr,
const SCEV *IncExpr,
ScalarEvolution&);
};
/// Helper for CollectChains to track multiple IV increment uses. Distinguish
/// between FarUsers that definitely cross IV increments and NearUsers that may
/// be used between IV increments.
struct ChainUsers {
SmallPtrSet<Instruction*, 4> FarUsers;
SmallPtrSet<Instruction*, 4> NearUsers;
};
/// This class holds state for the main loop strength reduction logic.
class LSRInstance {
IVUsers &IU;
ScalarEvolution &SE;
DominatorTree &DT;
LoopInfo &LI;
const TargetTransformInfo &TTI;
Loop *const L;
bool Changed;
/// This is the insert position that the current loop's induction variable
/// increment should be placed. In simple loops, this is the latch block's
/// terminator. But in more complicated cases, this is a position which will
/// dominate all the in-loop post-increment users.
Instruction *IVIncInsertPos;
/// Interesting factors between use strides.
SmallSetVector<int64_t, 8> Factors;
/// Interesting use types, to facilitate truncation reuse.
SmallSetVector<Type *, 4> Types;
/// The list of interesting uses.
SmallVector<LSRUse, 16> Uses;
/// Track which uses use which register candidates.
RegUseTracker RegUses;
// Limit the number of chains to avoid quadratic behavior. We don't expect to
// have more than a few IV increment chains in a loop. Missing a Chain falls
// back to normal LSR behavior for those uses.
static const unsigned MaxChains = 8;
/// IV users can form a chain of IV increments.
SmallVector<IVChain, MaxChains> IVChainVec;
/// IV users that belong to profitable IVChains.
SmallPtrSet<Use*, MaxChains> IVIncSet;
void OptimizeShadowIV();
bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse);
ICmpInst *OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse);
void OptimizeLoopTermCond();
void ChainInstruction(Instruction *UserInst, Instruction *IVOper,
SmallVectorImpl<ChainUsers> &ChainUsersVec);
void FinalizeChain(IVChain &Chain);
void CollectChains();
void GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts);
void CollectInterestingTypesAndFactors();
void CollectFixupsAndInitialFormulae();
// Support for sharing of LSRUses between LSRFixups.
typedef DenseMap<LSRUse::SCEVUseKindPair, size_t> UseMapTy;
UseMapTy UseMap;
bool reconcileNewOffset(LSRUse &LU, int64_t NewOffset, bool HasBaseReg,
LSRUse::KindType Kind, MemAccessTy AccessTy);
std::pair<size_t, int64_t> getUse(const SCEV *&Expr, LSRUse::KindType Kind,
MemAccessTy AccessTy);
void DeleteUse(LSRUse &LU, size_t LUIdx);
LSRUse *FindUseWithSimilarFormula(const Formula &F, const LSRUse &OrigLU);
void InsertInitialFormula(const SCEV *S, LSRUse &LU, size_t LUIdx);
void InsertSupplementalFormula(const SCEV *S, LSRUse &LU, size_t LUIdx);
void CountRegisters(const Formula &F, size_t LUIdx);
bool InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F);
void CollectLoopInvariantFixupsAndFormulae();
void GenerateReassociations(LSRUse &LU, unsigned LUIdx, Formula Base,
unsigned Depth = 0);
void GenerateReassociationsImpl(LSRUse &LU, unsigned LUIdx,
const Formula &Base, unsigned Depth,
size_t Idx, bool IsScaledReg = false);
void GenerateCombinations(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateSymbolicOffsetsImpl(LSRUse &LU, unsigned LUIdx,
const Formula &Base, size_t Idx,
bool IsScaledReg = false);
void GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateConstantOffsetsImpl(LSRUse &LU, unsigned LUIdx,
const Formula &Base,
const SmallVectorImpl<int64_t> &Worklist,
size_t Idx, bool IsScaledReg = false);
void GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateTruncates(LSRUse &LU, unsigned LUIdx, Formula Base);
void GenerateCrossUseConstantOffsets();
void GenerateAllReuseFormulae();
void FilterOutUndesirableDedicatedRegisters();
size_t EstimateSearchSpaceComplexity() const;
void NarrowSearchSpaceByDetectingSupersets();
void NarrowSearchSpaceByCollapsingUnrolledCode();
void NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters();
void NarrowSearchSpaceByPickingWinnerRegs();
void NarrowSearchSpaceUsingHeuristics();
void SolveRecurse(SmallVectorImpl<const Formula *> &Solution,
Cost &SolutionCost,
SmallVectorImpl<const Formula *> &Workspace,
const Cost &CurCost,
const SmallPtrSet<const SCEV *, 16> &CurRegs,
DenseSet<const SCEV *> &VisitedRegs) const;
void Solve(SmallVectorImpl<const Formula *> &Solution) const;
BasicBlock::iterator
HoistInsertPosition(BasicBlock::iterator IP,
const SmallVectorImpl<Instruction *> &Inputs) const;
BasicBlock::iterator
AdjustInsertPositionForExpand(BasicBlock::iterator IP,
const LSRFixup &LF,
const LSRUse &LU,
SCEVExpander &Rewriter) const;
Value *Expand(const LSRUse &LU, const LSRFixup &LF,
const Formula &F,
BasicBlock::iterator IP,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const;
void RewriteForPHI(PHINode *PN, const LSRUse &LU, const LSRFixup &LF,
const Formula &F,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const;
void Rewrite(const LSRUse &LU, const LSRFixup &LF,
const Formula &F,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const;
void ImplementSolution(const SmallVectorImpl<const Formula *> &Solution);
public:
LSRInstance(Loop *L, IVUsers &IU, ScalarEvolution &SE, DominatorTree &DT,
LoopInfo &LI, const TargetTransformInfo &TTI);
bool getChanged() const { return Changed; }
void print_factors_and_types(raw_ostream &OS) const;
void print_fixups(raw_ostream &OS) const;
void print_uses(raw_ostream &OS) const;
void print(raw_ostream &OS) const;
void dump() const;
};
}
/// If IV is used in a int-to-float cast inside the loop then try to eliminate
/// the cast operation.
void LSRInstance::OptimizeShadowIV() {
const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
return;
for (IVUsers::const_iterator UI = IU.begin(), E = IU.end();
UI != E; /* empty */) {
IVUsers::const_iterator CandidateUI = UI;
++UI;
Instruction *ShadowUse = CandidateUI->getUser();
Type *DestTy = nullptr;
bool IsSigned = false;
/* If shadow use is a int->float cast then insert a second IV
to eliminate this cast.
for (unsigned i = 0; i < n; ++i)
foo((double)i);
is transformed into
double d = 0.0;
for (unsigned i = 0; i < n; ++i, ++d)
foo(d);
*/
if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser())) {
IsSigned = false;
DestTy = UCast->getDestTy();
}
else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser())) {
IsSigned = true;
DestTy = SCast->getDestTy();
}
if (!DestTy) continue;
// If target does not support DestTy natively then do not apply
// this transformation.
if (!TTI.isTypeLegal(DestTy)) continue;
PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0));
if (!PH) continue;
if (PH->getNumIncomingValues() != 2) continue;
Type *SrcTy = PH->getType();
int Mantissa = DestTy->getFPMantissaWidth();
if (Mantissa == -1) continue;
if ((int)SE.getTypeSizeInBits(SrcTy) > Mantissa)
continue;
unsigned Entry, Latch;
if (PH->getIncomingBlock(0) == L->getLoopPreheader()) {
Entry = 0;
Latch = 1;
} else {
Entry = 1;
Latch = 0;
}
ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry));
if (!Init) continue;
Constant *NewInit = ConstantFP::get(DestTy, IsSigned ?
(double)Init->getSExtValue() :
(double)Init->getZExtValue());
BinaryOperator *Incr =
dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch));
if (!Incr) continue;
if (Incr->getOpcode() != Instruction::Add
&& Incr->getOpcode() != Instruction::Sub)
continue;
/* Initialize new IV, double d = 0.0 in above example. */
ConstantInt *C = nullptr;
if (Incr->getOperand(0) == PH)
C = dyn_cast<ConstantInt>(Incr->getOperand(1));
else if (Incr->getOperand(1) == PH)
C = dyn_cast<ConstantInt>(Incr->getOperand(0));
else
continue;
if (!C) continue;
// Ignore negative constants, as the code below doesn't handle them
// correctly. TODO: Remove this restriction.
if (!C->getValue().isStrictlyPositive()) continue;
/* Add new PHINode. */
PHINode *NewPH = PHINode::Create(DestTy, 2, "IV.S.", PH);
/* create new increment. '++d' in above example. */
Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue());
BinaryOperator *NewIncr =
BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ?
Instruction::FAdd : Instruction::FSub,
NewPH, CFP, "IV.S.next.", Incr);
NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry));
NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch));
/* Remove cast operation */
ShadowUse->replaceAllUsesWith(NewPH);
ShadowUse->eraseFromParent();
Changed = true;
break;
}
}
/// If Cond has an operand that is an expression of an IV, set the IV user and
/// stride information and return true, otherwise return false.
bool LSRInstance::FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse) {
for (IVStrideUse &U : IU)
if (U.getUser() == Cond) {
// NOTE: we could handle setcc instructions with multiple uses here, but
// InstCombine does it as well for simple uses, it's not clear that it
// occurs enough in real life to handle.
CondUse = &U;
return true;
}
return false;
}
/// Rewrite the loop's terminating condition if it uses a max computation.
///
/// This is a narrow solution to a specific, but acute, problem. For loops
/// like this:
///
/// i = 0;
/// do {
/// p[i] = 0.0;
/// } while (++i < n);
///
/// the trip count isn't just 'n', because 'n' might not be positive. And
/// unfortunately this can come up even for loops where the user didn't use
/// a C do-while loop. For example, seemingly well-behaved top-test loops
/// will commonly be lowered like this:
//
/// if (n > 0) {
/// i = 0;
/// do {
/// p[i] = 0.0;
/// } while (++i < n);
/// }
///
/// and then it's possible for subsequent optimization to obscure the if
/// test in such a way that indvars can't find it.
///
/// When indvars can't find the if test in loops like this, it creates a
/// max expression, which allows it to give the loop a canonical
/// induction variable:
///
/// i = 0;
/// max = n < 1 ? 1 : n;
/// do {
/// p[i] = 0.0;
/// } while (++i != max);
///
/// Canonical induction variables are necessary because the loop passes
/// are designed around them. The most obvious example of this is the
/// LoopInfo analysis, which doesn't remember trip count values. It
/// expects to be able to rediscover the trip count each time it is
/// needed, and it does this using a simple analysis that only succeeds if
/// the loop has a canonical induction variable.
///
/// However, when it comes time to generate code, the maximum operation
/// can be quite costly, especially if it's inside of an outer loop.
///
/// This function solves this problem by detecting this type of loop and
/// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting
/// the instructions for the maximum computation.
///
ICmpInst *LSRInstance::OptimizeMax(ICmpInst *Cond, IVStrideUse* &CondUse) {
// Check that the loop matches the pattern we're looking for.
if (Cond->getPredicate() != CmpInst::ICMP_EQ &&
Cond->getPredicate() != CmpInst::ICMP_NE)
return Cond;
SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1));
if (!Sel || !Sel->hasOneUse()) return Cond;
const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount))
return Cond;
const SCEV *One = SE.getConstant(BackedgeTakenCount->getType(), 1);
// Add one to the backedge-taken count to get the trip count.
const SCEV *IterationCount = SE.getAddExpr(One, BackedgeTakenCount);
if (IterationCount != SE.getSCEV(Sel)) return Cond;
// Check for a max calculation that matches the pattern. There's no check
// for ICMP_ULE here because the comparison would be with zero, which
// isn't interesting.
CmpInst::Predicate Pred = ICmpInst::BAD_ICMP_PREDICATE;
const SCEVNAryExpr *Max = nullptr;
if (const SCEVSMaxExpr *S = dyn_cast<SCEVSMaxExpr>(BackedgeTakenCount)) {
Pred = ICmpInst::ICMP_SLE;
Max = S;
} else if (const SCEVSMaxExpr *S = dyn_cast<SCEVSMaxExpr>(IterationCount)) {
Pred = ICmpInst::ICMP_SLT;
Max = S;
} else if (const SCEVUMaxExpr *U = dyn_cast<SCEVUMaxExpr>(IterationCount)) {
Pred = ICmpInst::ICMP_ULT;
Max = U;
} else {
// No match; bail.
return Cond;
}
// To handle a max with more than two operands, this optimization would
// require additional checking and setup.
if (Max->getNumOperands() != 2)
return Cond;
const SCEV *MaxLHS = Max->getOperand(0);
const SCEV *MaxRHS = Max->getOperand(1);
// ScalarEvolution canonicalizes constants to the left. For < and >, look
// for a comparison with 1. For <= and >=, a comparison with zero.
if (!MaxLHS ||
(ICmpInst::isTrueWhenEqual(Pred) ? !MaxLHS->isZero() : (MaxLHS != One)))
return Cond;
// Check the relevant induction variable for conformance to
// the pattern.
const SCEV *IV = SE.getSCEV(Cond->getOperand(0));
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV);
if (!AR || !AR->isAffine() ||
AR->getStart() != One ||
AR->getStepRecurrence(SE) != One)
return Cond;
assert(AR->getLoop() == L &&
"Loop condition operand is an addrec in a different loop!");
// Check the right operand of the select, and remember it, as it will
// be used in the new comparison instruction.
Value *NewRHS = nullptr;
if (ICmpInst::isTrueWhenEqual(Pred)) {
// Look for n+1, and grab n.
if (AddOperator *BO = dyn_cast<AddOperator>(Sel->getOperand(1)))
if (ConstantInt *BO1 = dyn_cast<ConstantInt>(BO->getOperand(1)))
if (BO1->isOne() && SE.getSCEV(BO->getOperand(0)) == MaxRHS)
NewRHS = BO->getOperand(0);
if (AddOperator *BO = dyn_cast<AddOperator>(Sel->getOperand(2)))
if (ConstantInt *BO1 = dyn_cast<ConstantInt>(BO->getOperand(1)))
if (BO1->isOne() && SE.getSCEV(BO->getOperand(0)) == MaxRHS)
NewRHS = BO->getOperand(0);
if (!NewRHS)
return Cond;
} else if (SE.getSCEV(Sel->getOperand(1)) == MaxRHS)
NewRHS = Sel->getOperand(1);
else if (SE.getSCEV(Sel->getOperand(2)) == MaxRHS)
NewRHS = Sel->getOperand(2);
else if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(MaxRHS))
NewRHS = SU->getValue();
else
// Max doesn't match expected pattern.
return Cond;
// Determine the new comparison opcode. It may be signed or unsigned,
// and the original comparison may be either equality or inequality.
if (Cond->getPredicate() == CmpInst::ICMP_EQ)
Pred = CmpInst::getInversePredicate(Pred);
// Ok, everything looks ok to change the condition into an SLT or SGE and
// delete the max calculation.
ICmpInst *NewCond =
new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp");
// Delete the max calculation instructions.
Cond->replaceAllUsesWith(NewCond);
CondUse->setUser(NewCond);
Instruction *Cmp = cast<Instruction>(Sel->getOperand(0));
Cond->eraseFromParent();
Sel->eraseFromParent();
if (Cmp->use_empty())
Cmp->eraseFromParent();
return NewCond;
}
/// Change loop terminating condition to use the postinc iv when possible.
void
LSRInstance::OptimizeLoopTermCond() {
SmallPtrSet<Instruction *, 4> PostIncs;
// We need a different set of heuristics for rotated and non-rotated loops.
// If a loop is rotated then the latch is also the backedge, so inserting
// post-inc expressions just before the latch is ideal. To reduce live ranges
// it also makes sense to rewrite terminating conditions to use post-inc
// expressions.
//
// If the loop is not rotated then the latch is not a backedge; the latch
// check is done in the loop head. Adding post-inc expressions before the
// latch will cause overlapping live-ranges of pre-inc and post-inc expressions
// in the loop body. In this case we do *not* want to use post-inc expressions
// in the latch check, and we want to insert post-inc expressions before
// the backedge.
BasicBlock *LatchBlock = L->getLoopLatch();
SmallVector<BasicBlock*, 8> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
if (llvm::all_of(ExitingBlocks, [&LatchBlock](const BasicBlock *BB) {
return LatchBlock != BB;
})) {
// The backedge doesn't exit the loop; treat this as a head-tested loop.
IVIncInsertPos = LatchBlock->getTerminator();
return;
}
// Otherwise treat this as a rotated loop.
for (BasicBlock *ExitingBlock : ExitingBlocks) {
// Get the terminating condition for the loop if possible. If we
// can, we want to change it to use a post-incremented version of its
// induction variable, to allow coalescing the live ranges for the IV into
// one register value.
BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (!TermBr)
continue;
// FIXME: Overly conservative, termination condition could be an 'or' etc..
if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition()))
continue;
// Search IVUsesByStride to find Cond's IVUse if there is one.
IVStrideUse *CondUse = nullptr;
ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition());
if (!FindIVUserForCond(Cond, CondUse))
continue;
// If the trip count is computed in terms of a max (due to ScalarEvolution
// being unable to find a sufficient guard, for example), change the loop
// comparison to use SLT or ULT instead of NE.
// One consequence of doing this now is that it disrupts the count-down
// optimization. That's not always a bad thing though, because in such
// cases it may still be worthwhile to avoid a max.
Cond = OptimizeMax(Cond, CondUse);
// If this exiting block dominates the latch block, it may also use
// the post-inc value if it won't be shared with other uses.
// Check for dominance.
if (!DT.dominates(ExitingBlock, LatchBlock))
continue;
// Conservatively avoid trying to use the post-inc value in non-latch
// exits if there may be pre-inc users in intervening blocks.
if (LatchBlock != ExitingBlock)
for (IVUsers::const_iterator UI = IU.begin(), E = IU.end(); UI != E; ++UI)
// Test if the use is reachable from the exiting block. This dominator
// query is a conservative approximation of reachability.
if (&*UI != CondUse &&
!DT.properlyDominates(UI->getUser()->getParent(), ExitingBlock)) {
// Conservatively assume there may be reuse if the quotient of their
// strides could be a legal scale.
const SCEV *A = IU.getStride(*CondUse, L);
const SCEV *B = IU.getStride(*UI, L);
if (!A || !B) continue;
if (SE.getTypeSizeInBits(A->getType()) !=
SE.getTypeSizeInBits(B->getType())) {
if (SE.getTypeSizeInBits(A->getType()) >
SE.getTypeSizeInBits(B->getType()))
B = SE.getSignExtendExpr(B, A->getType());
else
A = SE.getSignExtendExpr(A, B->getType());
}
if (const SCEVConstant *D =
dyn_cast_or_null<SCEVConstant>(getExactSDiv(B, A, SE))) {
const ConstantInt *C = D->getValue();
// Stride of one or negative one can have reuse with non-addresses.
if (C->isOne() || C->isAllOnesValue())
goto decline_post_inc;
// Avoid weird situations.
if (C->getValue().getMinSignedBits() >= 64 ||
C->getValue().isMinSignedValue())
goto decline_post_inc;
// Check for possible scaled-address reuse.
MemAccessTy AccessTy = getAccessType(UI->getUser());
int64_t Scale = C->getSExtValue();
if (TTI.isLegalAddressingMode(AccessTy.MemTy, /*BaseGV=*/nullptr,
/*BaseOffset=*/0,
/*HasBaseReg=*/false, Scale,
AccessTy.AddrSpace))
goto decline_post_inc;
Scale = -Scale;
if (TTI.isLegalAddressingMode(AccessTy.MemTy, /*BaseGV=*/nullptr,
/*BaseOffset=*/0,
/*HasBaseReg=*/false, Scale,
AccessTy.AddrSpace))
goto decline_post_inc;
}
}
DEBUG(dbgs() << " Change loop exiting icmp to use postinc iv: "
<< *Cond << '\n');
// It's possible for the setcc instruction to be anywhere in the loop, and
// possible for it to have multiple users. If it is not immediately before
// the exiting block branch, move it.
if (&*++BasicBlock::iterator(Cond) != TermBr) {
if (Cond->hasOneUse()) {
Cond->moveBefore(TermBr);
} else {
// Clone the terminating condition and insert into the loopend.
ICmpInst *OldCond = Cond;
Cond = cast<ICmpInst>(Cond->clone());
Cond->setName(L->getHeader()->getName() + ".termcond");
ExitingBlock->getInstList().insert(TermBr->getIterator(), Cond);
// Clone the IVUse, as the old use still exists!
CondUse = &IU.AddUser(Cond, CondUse->getOperandValToReplace());
TermBr->replaceUsesOfWith(OldCond, Cond);
}
}
// If we get to here, we know that we can transform the setcc instruction to
// use the post-incremented version of the IV, allowing us to coalesce the
// live ranges for the IV correctly.
CondUse->transformToPostInc(L);
Changed = true;
PostIncs.insert(Cond);
decline_post_inc:;
}
// Determine an insertion point for the loop induction variable increment. It
// must dominate all the post-inc comparisons we just set up, and it must
// dominate the loop latch edge.
IVIncInsertPos = L->getLoopLatch()->getTerminator();
for (Instruction *Inst : PostIncs) {
BasicBlock *BB =
DT.findNearestCommonDominator(IVIncInsertPos->getParent(),
Inst->getParent());
if (BB == Inst->getParent())
IVIncInsertPos = Inst;
else if (BB != IVIncInsertPos->getParent())
IVIncInsertPos = BB->getTerminator();
}
}
/// Determine if the given use can accommodate a fixup at the given offset and
/// other details. If so, update the use and return true.
bool LSRInstance::reconcileNewOffset(LSRUse &LU, int64_t NewOffset,
bool HasBaseReg, LSRUse::KindType Kind,
MemAccessTy AccessTy) {
int64_t NewMinOffset = LU.MinOffset;
int64_t NewMaxOffset = LU.MaxOffset;
MemAccessTy NewAccessTy = AccessTy;
// Check for a mismatched kind. It's tempting to collapse mismatched kinds to
// something conservative, however this can pessimize in the case that one of
// the uses will have all its uses outside the loop, for example.
if (LU.Kind != Kind)
return false;
// Check for a mismatched access type, and fall back conservatively as needed.
// TODO: Be less conservative when the type is similar and can use the same
// addressing modes.
if (Kind == LSRUse::Address) {
if (AccessTy != LU.AccessTy)
NewAccessTy = MemAccessTy::getUnknown(AccessTy.MemTy->getContext());
}
// Conservatively assume HasBaseReg is true for now.
if (NewOffset < LU.MinOffset) {
if (!isAlwaysFoldable(TTI, Kind, NewAccessTy, /*BaseGV=*/nullptr,
LU.MaxOffset - NewOffset, HasBaseReg))
return false;
NewMinOffset = NewOffset;
} else if (NewOffset > LU.MaxOffset) {
if (!isAlwaysFoldable(TTI, Kind, NewAccessTy, /*BaseGV=*/nullptr,
NewOffset - LU.MinOffset, HasBaseReg))
return false;
NewMaxOffset = NewOffset;
}
// Update the use.
LU.MinOffset = NewMinOffset;
LU.MaxOffset = NewMaxOffset;
LU.AccessTy = NewAccessTy;
return true;
}
/// Return an LSRUse index and an offset value for a fixup which needs the given
/// expression, with the given kind and optional access type. Either reuse an
/// existing use or create a new one, as needed.
std::pair<size_t, int64_t> LSRInstance::getUse(const SCEV *&Expr,
LSRUse::KindType Kind,
MemAccessTy AccessTy) {
const SCEV *Copy = Expr;
int64_t Offset = ExtractImmediate(Expr, SE);
// Basic uses can't accept any offset, for example.
if (!isAlwaysFoldable(TTI, Kind, AccessTy, /*BaseGV=*/ nullptr,
Offset, /*HasBaseReg=*/ true)) {
Expr = Copy;
Offset = 0;
}
std::pair<UseMapTy::iterator, bool> P =
UseMap.insert(std::make_pair(LSRUse::SCEVUseKindPair(Expr, Kind), 0));
if (!P.second) {
// A use already existed with this base.
size_t LUIdx = P.first->second;
LSRUse &LU = Uses[LUIdx];
if (reconcileNewOffset(LU, Offset, /*HasBaseReg=*/true, Kind, AccessTy))
// Reuse this use.
return std::make_pair(LUIdx, Offset);
}
// Create a new use.
size_t LUIdx = Uses.size();
P.first->second = LUIdx;
Uses.push_back(LSRUse(Kind, AccessTy));
LSRUse &LU = Uses[LUIdx];
LU.MinOffset = Offset;
LU.MaxOffset = Offset;
return std::make_pair(LUIdx, Offset);
}
/// Delete the given use from the Uses list.
void LSRInstance::DeleteUse(LSRUse &LU, size_t LUIdx) {
if (&LU != &Uses.back())
std::swap(LU, Uses.back());
Uses.pop_back();
// Update RegUses.
RegUses.swapAndDropUse(LUIdx, Uses.size());
}
/// Look for a use distinct from OrigLU which is has a formula that has the same
/// registers as the given formula.
LSRUse *
LSRInstance::FindUseWithSimilarFormula(const Formula &OrigF,
const LSRUse &OrigLU) {
// Search all uses for the formula. This could be more clever.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
// Check whether this use is close enough to OrigLU, to see whether it's
// worthwhile looking through its formulae.
// Ignore ICmpZero uses because they may contain formulae generated by
// GenerateICmpZeroScales, in which case adding fixup offsets may
// be invalid.
if (&LU != &OrigLU &&
LU.Kind != LSRUse::ICmpZero &&
LU.Kind == OrigLU.Kind && OrigLU.AccessTy == LU.AccessTy &&
LU.WidestFixupType == OrigLU.WidestFixupType &&
LU.HasFormulaWithSameRegs(OrigF)) {
// Scan through this use's formulae.
for (const Formula &F : LU.Formulae) {
// Check to see if this formula has the same registers and symbols
// as OrigF.
if (F.BaseRegs == OrigF.BaseRegs &&
F.ScaledReg == OrigF.ScaledReg &&
F.BaseGV == OrigF.BaseGV &&
F.Scale == OrigF.Scale &&
F.UnfoldedOffset == OrigF.UnfoldedOffset) {
if (F.BaseOffset == 0)
return &LU;
// This is the formula where all the registers and symbols matched;
// there aren't going to be any others. Since we declined it, we
// can skip the rest of the formulae and proceed to the next LSRUse.
break;
}
}
}
}
// Nothing looked good.
return nullptr;
}
void LSRInstance::CollectInterestingTypesAndFactors() {
SmallSetVector<const SCEV *, 4> Strides;
// Collect interesting types and strides.
SmallVector<const SCEV *, 4> Worklist;
for (const IVStrideUse &U : IU) {
const SCEV *Expr = IU.getExpr(U);
// Collect interesting types.
Types.insert(SE.getEffectiveSCEVType(Expr->getType()));
// Add strides for mentioned loops.
Worklist.push_back(Expr);
do {
const SCEV *S = Worklist.pop_back_val();
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
if (AR->getLoop() == L)
Strides.insert(AR->getStepRecurrence(SE));
Worklist.push_back(AR->getStart());
} else if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
Worklist.append(Add->op_begin(), Add->op_end());
}
} while (!Worklist.empty());
}
// Compute interesting factors from the set of interesting strides.
for (SmallSetVector<const SCEV *, 4>::const_iterator
I = Strides.begin(), E = Strides.end(); I != E; ++I)
for (SmallSetVector<const SCEV *, 4>::const_iterator NewStrideIter =
std::next(I); NewStrideIter != E; ++NewStrideIter) {
const SCEV *OldStride = *I;
const SCEV *NewStride = *NewStrideIter;
if (SE.getTypeSizeInBits(OldStride->getType()) !=
SE.getTypeSizeInBits(NewStride->getType())) {
if (SE.getTypeSizeInBits(OldStride->getType()) >
SE.getTypeSizeInBits(NewStride->getType()))
NewStride = SE.getSignExtendExpr(NewStride, OldStride->getType());
else
OldStride = SE.getSignExtendExpr(OldStride, NewStride->getType());
}
if (const SCEVConstant *Factor =
dyn_cast_or_null<SCEVConstant>(getExactSDiv(NewStride, OldStride,
SE, true))) {
if (Factor->getAPInt().getMinSignedBits() <= 64)
Factors.insert(Factor->getAPInt().getSExtValue());
} else if (const SCEVConstant *Factor =
dyn_cast_or_null<SCEVConstant>(getExactSDiv(OldStride,
NewStride,
SE, true))) {
if (Factor->getAPInt().getMinSignedBits() <= 64)
Factors.insert(Factor->getAPInt().getSExtValue());
}
}
// If all uses use the same type, don't bother looking for truncation-based
// reuse.
if (Types.size() == 1)
Types.clear();
DEBUG(print_factors_and_types(dbgs()));
}
/// Helper for CollectChains that finds an IV operand (computed by an AddRec in
/// this loop) within [OI,OE) or returns OE. If IVUsers mapped Instructions to
/// IVStrideUses, we could partially skip this.
static User::op_iterator
findIVOperand(User::op_iterator OI, User::op_iterator OE,
Loop *L, ScalarEvolution &SE) {
for(; OI != OE; ++OI) {
if (Instruction *Oper = dyn_cast<Instruction>(*OI)) {
if (!SE.isSCEVable(Oper->getType()))
continue;
if (const SCEVAddRecExpr *AR =
dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Oper))) {
if (AR->getLoop() == L)
break;
}
}
}
return OI;
}
/// IVChain logic must consistenctly peek base TruncInst operands, so wrap it in
/// a convenient helper.
static Value *getWideOperand(Value *Oper) {
if (TruncInst *Trunc = dyn_cast<TruncInst>(Oper))
return Trunc->getOperand(0);
return Oper;
}
/// Return true if we allow an IV chain to include both types.
static bool isCompatibleIVType(Value *LVal, Value *RVal) {
Type *LType = LVal->getType();
Type *RType = RVal->getType();
return (LType == RType) || (LType->isPointerTy() && RType->isPointerTy());
}
/// Return an approximation of this SCEV expression's "base", or NULL for any
/// constant. Returning the expression itself is conservative. Returning a
/// deeper subexpression is more precise and valid as long as it isn't less
/// complex than another subexpression. For expressions involving multiple
/// unscaled values, we need to return the pointer-type SCEVUnknown. This avoids
/// forming chains across objects, such as: PrevOper==a[i], IVOper==b[i],
/// IVInc==b-a.
///
/// Since SCEVUnknown is the rightmost type, and pointers are the rightmost
/// SCEVUnknown, we simply return the rightmost SCEV operand.
static const SCEV *getExprBase(const SCEV *S) {
switch (S->getSCEVType()) {
default: // uncluding scUnknown.
return S;
case scConstant:
return nullptr;
case scTruncate:
return getExprBase(cast<SCEVTruncateExpr>(S)->getOperand());
case scZeroExtend:
return getExprBase(cast<SCEVZeroExtendExpr>(S)->getOperand());
case scSignExtend:
return getExprBase(cast<SCEVSignExtendExpr>(S)->getOperand());
case scAddExpr: {
// Skip over scaled operands (scMulExpr) to follow add operands as long as
// there's nothing more complex.
// FIXME: not sure if we want to recognize negation.
const SCEVAddExpr *Add = cast<SCEVAddExpr>(S);
for (std::reverse_iterator<SCEVAddExpr::op_iterator> I(Add->op_end()),
E(Add->op_begin()); I != E; ++I) {
const SCEV *SubExpr = *I;
if (SubExpr->getSCEVType() == scAddExpr)
return getExprBase(SubExpr);
if (SubExpr->getSCEVType() != scMulExpr)
return SubExpr;
}
return S; // all operands are scaled, be conservative.
}
case scAddRecExpr:
return getExprBase(cast<SCEVAddRecExpr>(S)->getStart());
}
}
/// Return true if the chain increment is profitable to expand into a loop
/// invariant value, which may require its own register. A profitable chain
/// increment will be an offset relative to the same base. We allow such offsets
/// to potentially be used as chain increment as long as it's not obviously
/// expensive to expand using real instructions.
bool IVChain::isProfitableIncrement(const SCEV *OperExpr,
const SCEV *IncExpr,
ScalarEvolution &SE) {
// Aggressively form chains when -stress-ivchain.
if (StressIVChain)
return true;
// Do not replace a constant offset from IV head with a nonconstant IV
// increment.
if (!isa<SCEVConstant>(IncExpr)) {
const SCEV *HeadExpr = SE.getSCEV(getWideOperand(Incs[0].IVOperand));
if (isa<SCEVConstant>(SE.getMinusSCEV(OperExpr, HeadExpr)))
return 0;
}
SmallPtrSet<const SCEV*, 8> Processed;
return !isHighCostExpansion(IncExpr, Processed, SE);
}
/// Return true if the number of registers needed for the chain is estimated to
/// be less than the number required for the individual IV users. First prohibit
/// any IV users that keep the IV live across increments (the Users set should
/// be empty). Next count the number and type of increments in the chain.
///
/// Chaining IVs can lead to considerable code bloat if ISEL doesn't
/// effectively use postinc addressing modes. Only consider it profitable it the
/// increments can be computed in fewer registers when chained.
///
/// TODO: Consider IVInc free if it's already used in another chains.
static bool
isProfitableChain(IVChain &Chain, SmallPtrSetImpl<Instruction*> &Users,
ScalarEvolution &SE, const TargetTransformInfo &TTI) {
if (StressIVChain)
return true;
if (!Chain.hasIncs())
return false;
if (!Users.empty()) {
DEBUG(dbgs() << "Chain: " << *Chain.Incs[0].UserInst << " users:\n";
for (Instruction *Inst : Users) {
dbgs() << " " << *Inst << "\n";
});
return false;
}
assert(!Chain.Incs.empty() && "empty IV chains are not allowed");
// The chain itself may require a register, so intialize cost to 1.
int cost = 1;
// A complete chain likely eliminates the need for keeping the original IV in
// a register. LSR does not currently know how to form a complete chain unless
// the header phi already exists.
if (isa<PHINode>(Chain.tailUserInst())
&& SE.getSCEV(Chain.tailUserInst()) == Chain.Incs[0].IncExpr) {
--cost;
}
const SCEV *LastIncExpr = nullptr;
unsigned NumConstIncrements = 0;
unsigned NumVarIncrements = 0;
unsigned NumReusedIncrements = 0;
for (const IVInc &Inc : Chain) {
if (Inc.IncExpr->isZero())
continue;
// Incrementing by zero or some constant is neutral. We assume constants can
// be folded into an addressing mode or an add's immediate operand.
if (isa<SCEVConstant>(Inc.IncExpr)) {
++NumConstIncrements;
continue;
}
if (Inc.IncExpr == LastIncExpr)
++NumReusedIncrements;
else
++NumVarIncrements;
LastIncExpr = Inc.IncExpr;
}
// An IV chain with a single increment is handled by LSR's postinc
// uses. However, a chain with multiple increments requires keeping the IV's
// value live longer than it needs to be if chained.
if (NumConstIncrements > 1)
--cost;
// Materializing increment expressions in the preheader that didn't exist in
// the original code may cost a register. For example, sign-extended array
// indices can produce ridiculous increments like this:
// IV + ((sext i32 (2 * %s) to i64) + (-1 * (sext i32 %s to i64)))
cost += NumVarIncrements;
// Reusing variable increments likely saves a register to hold the multiple of
// the stride.
cost -= NumReusedIncrements;
DEBUG(dbgs() << "Chain: " << *Chain.Incs[0].UserInst << " Cost: " << cost
<< "\n");
return cost < 0;
}
/// Add this IV user to an existing chain or make it the head of a new chain.
void LSRInstance::ChainInstruction(Instruction *UserInst, Instruction *IVOper,
SmallVectorImpl<ChainUsers> &ChainUsersVec) {
// When IVs are used as types of varying widths, they are generally converted
// to a wider type with some uses remaining narrow under a (free) trunc.
Value *const NextIV = getWideOperand(IVOper);
const SCEV *const OperExpr = SE.getSCEV(NextIV);
const SCEV *const OperExprBase = getExprBase(OperExpr);
// Visit all existing chains. Check if its IVOper can be computed as a
// profitable loop invariant increment from the last link in the Chain.
unsigned ChainIdx = 0, NChains = IVChainVec.size();
const SCEV *LastIncExpr = nullptr;
for (; ChainIdx < NChains; ++ChainIdx) {
IVChain &Chain = IVChainVec[ChainIdx];
// Prune the solution space aggressively by checking that both IV operands
// are expressions that operate on the same unscaled SCEVUnknown. This
// "base" will be canceled by the subsequent getMinusSCEV call. Checking
// first avoids creating extra SCEV expressions.
if (!StressIVChain && Chain.ExprBase != OperExprBase)
continue;
Value *PrevIV = getWideOperand(Chain.Incs.back().IVOperand);
if (!isCompatibleIVType(PrevIV, NextIV))
continue;
// A phi node terminates a chain.
if (isa<PHINode>(UserInst) && isa<PHINode>(Chain.tailUserInst()))
continue;
// The increment must be loop-invariant so it can be kept in a register.
const SCEV *PrevExpr = SE.getSCEV(PrevIV);
const SCEV *IncExpr = SE.getMinusSCEV(OperExpr, PrevExpr);
if (!SE.isLoopInvariant(IncExpr, L))
continue;
if (Chain.isProfitableIncrement(OperExpr, IncExpr, SE)) {
LastIncExpr = IncExpr;
break;
}
}
// If we haven't found a chain, create a new one, unless we hit the max. Don't
// bother for phi nodes, because they must be last in the chain.
if (ChainIdx == NChains) {
if (isa<PHINode>(UserInst))
return;
if (NChains >= MaxChains && !StressIVChain) {
DEBUG(dbgs() << "IV Chain Limit\n");
return;
}
LastIncExpr = OperExpr;
// IVUsers may have skipped over sign/zero extensions. We don't currently
// attempt to form chains involving extensions unless they can be hoisted
// into this loop's AddRec.
if (!isa<SCEVAddRecExpr>(LastIncExpr))
return;
++NChains;
IVChainVec.push_back(IVChain(IVInc(UserInst, IVOper, LastIncExpr),
OperExprBase));
ChainUsersVec.resize(NChains);
DEBUG(dbgs() << "IV Chain#" << ChainIdx << " Head: (" << *UserInst
<< ") IV=" << *LastIncExpr << "\n");
} else {
DEBUG(dbgs() << "IV Chain#" << ChainIdx << " Inc: (" << *UserInst
<< ") IV+" << *LastIncExpr << "\n");
// Add this IV user to the end of the chain.
IVChainVec[ChainIdx].add(IVInc(UserInst, IVOper, LastIncExpr));
}
IVChain &Chain = IVChainVec[ChainIdx];
SmallPtrSet<Instruction*,4> &NearUsers = ChainUsersVec[ChainIdx].NearUsers;
// This chain's NearUsers become FarUsers.
if (!LastIncExpr->isZero()) {
ChainUsersVec[ChainIdx].FarUsers.insert(NearUsers.begin(),
NearUsers.end());
NearUsers.clear();
}
// All other uses of IVOperand become near uses of the chain.
// We currently ignore intermediate values within SCEV expressions, assuming
// they will eventually be used be the current chain, or can be computed
// from one of the chain increments. To be more precise we could
// transitively follow its user and only add leaf IV users to the set.
for (User *U : IVOper->users()) {
Instruction *OtherUse = dyn_cast<Instruction>(U);
if (!OtherUse)
continue;
// Uses in the chain will no longer be uses if the chain is formed.
// Include the head of the chain in this iteration (not Chain.begin()).
IVChain::const_iterator IncIter = Chain.Incs.begin();
IVChain::const_iterator IncEnd = Chain.Incs.end();
for( ; IncIter != IncEnd; ++IncIter) {
if (IncIter->UserInst == OtherUse)
break;
}
if (IncIter != IncEnd)
continue;
if (SE.isSCEVable(OtherUse->getType())
&& !isa<SCEVUnknown>(SE.getSCEV(OtherUse))
&& IU.isIVUserOrOperand(OtherUse)) {
continue;
}
NearUsers.insert(OtherUse);
}
// Since this user is part of the chain, it's no longer considered a use
// of the chain.
ChainUsersVec[ChainIdx].FarUsers.erase(UserInst);
}
/// Populate the vector of Chains.
///
/// This decreases ILP at the architecture level. Targets with ample registers,
/// multiple memory ports, and no register renaming probably don't want
/// this. However, such targets should probably disable LSR altogether.
///
/// The job of LSR is to make a reasonable choice of induction variables across
/// the loop. Subsequent passes can easily "unchain" computation exposing more
/// ILP *within the loop* if the target wants it.
///
/// Finding the best IV chain is potentially a scheduling problem. Since LSR
/// will not reorder memory operations, it will recognize this as a chain, but
/// will generate redundant IV increments. Ideally this would be corrected later
/// by a smart scheduler:
/// = A[i]
/// = A[i+x]
/// A[i] =
/// A[i+x] =
///
/// TODO: Walk the entire domtree within this loop, not just the path to the
/// loop latch. This will discover chains on side paths, but requires
/// maintaining multiple copies of the Chains state.
void LSRInstance::CollectChains() {
DEBUG(dbgs() << "Collecting IV Chains.\n");
SmallVector<ChainUsers, 8> ChainUsersVec;
SmallVector<BasicBlock *,8> LatchPath;
BasicBlock *LoopHeader = L->getHeader();
for (DomTreeNode *Rung = DT.getNode(L->getLoopLatch());
Rung->getBlock() != LoopHeader; Rung = Rung->getIDom()) {
LatchPath.push_back(Rung->getBlock());
}
LatchPath.push_back(LoopHeader);
// Walk the instruction stream from the loop header to the loop latch.
for (BasicBlock *BB : reverse(LatchPath)) {
for (Instruction &I : *BB) {
// Skip instructions that weren't seen by IVUsers analysis.
if (isa<PHINode>(I) || !IU.isIVUserOrOperand(&I))
continue;
// Ignore users that are part of a SCEV expression. This way we only
// consider leaf IV Users. This effectively rediscovers a portion of
// IVUsers analysis but in program order this time.
if (SE.isSCEVable(I.getType()) && !isa<SCEVUnknown>(SE.getSCEV(&I)))
continue;
// Remove this instruction from any NearUsers set it may be in.
for (unsigned ChainIdx = 0, NChains = IVChainVec.size();
ChainIdx < NChains; ++ChainIdx) {
ChainUsersVec[ChainIdx].NearUsers.erase(&I);
}
// Search for operands that can be chained.
SmallPtrSet<Instruction*, 4> UniqueOperands;
User::op_iterator IVOpEnd = I.op_end();
User::op_iterator IVOpIter = findIVOperand(I.op_begin(), IVOpEnd, L, SE);
while (IVOpIter != IVOpEnd) {
Instruction *IVOpInst = cast<Instruction>(*IVOpIter);
if (UniqueOperands.insert(IVOpInst).second)
ChainInstruction(&I, IVOpInst, ChainUsersVec);
IVOpIter = findIVOperand(std::next(IVOpIter), IVOpEnd, L, SE);
}
} // Continue walking down the instructions.
} // Continue walking down the domtree.
// Visit phi backedges to determine if the chain can generate the IV postinc.
for (BasicBlock::iterator I = L->getHeader()->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
if (!SE.isSCEVable(PN->getType()))
continue;
Instruction *IncV =
dyn_cast<Instruction>(PN->getIncomingValueForBlock(L->getLoopLatch()));
if (IncV)
ChainInstruction(PN, IncV, ChainUsersVec);
}
// Remove any unprofitable chains.
unsigned ChainIdx = 0;
for (unsigned UsersIdx = 0, NChains = IVChainVec.size();
UsersIdx < NChains; ++UsersIdx) {
if (!isProfitableChain(IVChainVec[UsersIdx],
ChainUsersVec[UsersIdx].FarUsers, SE, TTI))
continue;
// Preserve the chain at UsesIdx.
if (ChainIdx != UsersIdx)
IVChainVec[ChainIdx] = IVChainVec[UsersIdx];
FinalizeChain(IVChainVec[ChainIdx]);
++ChainIdx;
}
IVChainVec.resize(ChainIdx);
}
void LSRInstance::FinalizeChain(IVChain &Chain) {
assert(!Chain.Incs.empty() && "empty IV chains are not allowed");
DEBUG(dbgs() << "Final Chain: " << *Chain.Incs[0].UserInst << "\n");
for (const IVInc &Inc : Chain) {
DEBUG(dbgs() << " Inc: " << Inc.UserInst << "\n");
auto UseI = find(Inc.UserInst->operands(), Inc.IVOperand);
assert(UseI != Inc.UserInst->op_end() && "cannot find IV operand");
IVIncSet.insert(UseI);
}
}
/// Return true if the IVInc can be folded into an addressing mode.
static bool canFoldIVIncExpr(const SCEV *IncExpr, Instruction *UserInst,
Value *Operand, const TargetTransformInfo &TTI) {
const SCEVConstant *IncConst = dyn_cast<SCEVConstant>(IncExpr);
if (!IncConst || !isAddressUse(UserInst, Operand))
return false;
if (IncConst->getAPInt().getMinSignedBits() > 64)
return false;
MemAccessTy AccessTy = getAccessType(UserInst);
int64_t IncOffset = IncConst->getValue()->getSExtValue();
if (!isAlwaysFoldable(TTI, LSRUse::Address, AccessTy, /*BaseGV=*/nullptr,
IncOffset, /*HaseBaseReg=*/false))
return false;
return true;
}
/// Generate an add or subtract for each IVInc in a chain to materialize the IV
/// user's operand from the previous IV user's operand.
void LSRInstance::GenerateIVChain(const IVChain &Chain, SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) {
// Find the new IVOperand for the head of the chain. It may have been replaced
// by LSR.
const IVInc &Head = Chain.Incs[0];
User::op_iterator IVOpEnd = Head.UserInst->op_end();
// findIVOperand returns IVOpEnd if it can no longer find a valid IV user.
User::op_iterator IVOpIter = findIVOperand(Head.UserInst->op_begin(),
IVOpEnd, L, SE);
Value *IVSrc = nullptr;
while (IVOpIter != IVOpEnd) {
IVSrc = getWideOperand(*IVOpIter);
// If this operand computes the expression that the chain needs, we may use
// it. (Check this after setting IVSrc which is used below.)
//
// Note that if Head.IncExpr is wider than IVSrc, then this phi is too
// narrow for the chain, so we can no longer use it. We do allow using a
// wider phi, assuming the LSR checked for free truncation. In that case we
// should already have a truncate on this operand such that
// getSCEV(IVSrc) == IncExpr.
if (SE.getSCEV(*IVOpIter) == Head.IncExpr
|| SE.getSCEV(IVSrc) == Head.IncExpr) {
break;
}
IVOpIter = findIVOperand(std::next(IVOpIter), IVOpEnd, L, SE);
}
if (IVOpIter == IVOpEnd) {
// Gracefully give up on this chain.
DEBUG(dbgs() << "Concealed chain head: " << *Head.UserInst << "\n");
return;
}
DEBUG(dbgs() << "Generate chain at: " << *IVSrc << "\n");
Type *IVTy = IVSrc->getType();
Type *IntTy = SE.getEffectiveSCEVType(IVTy);
const SCEV *LeftOverExpr = nullptr;
for (const IVInc &Inc : Chain) {
Instruction *InsertPt = Inc.UserInst;
if (isa<PHINode>(InsertPt))
InsertPt = L->getLoopLatch()->getTerminator();
// IVOper will replace the current IV User's operand. IVSrc is the IV
// value currently held in a register.
Value *IVOper = IVSrc;
if (!Inc.IncExpr->isZero()) {
// IncExpr was the result of subtraction of two narrow values, so must
// be signed.
const SCEV *IncExpr = SE.getNoopOrSignExtend(Inc.IncExpr, IntTy);
LeftOverExpr = LeftOverExpr ?
SE.getAddExpr(LeftOverExpr, IncExpr) : IncExpr;
}
if (LeftOverExpr && !LeftOverExpr->isZero()) {
// Expand the IV increment.
Rewriter.clearPostInc();
Value *IncV = Rewriter.expandCodeFor(LeftOverExpr, IntTy, InsertPt);
const SCEV *IVOperExpr = SE.getAddExpr(SE.getUnknown(IVSrc),
SE.getUnknown(IncV));
IVOper = Rewriter.expandCodeFor(IVOperExpr, IVTy, InsertPt);
// If an IV increment can't be folded, use it as the next IV value.
if (!canFoldIVIncExpr(LeftOverExpr, Inc.UserInst, Inc.IVOperand, TTI)) {
assert(IVTy == IVOper->getType() && "inconsistent IV increment type");
IVSrc = IVOper;
LeftOverExpr = nullptr;
}
}
Type *OperTy = Inc.IVOperand->getType();
if (IVTy != OperTy) {
assert(SE.getTypeSizeInBits(IVTy) >= SE.getTypeSizeInBits(OperTy) &&
"cannot extend a chained IV");
IRBuilder<> Builder(InsertPt);
IVOper = Builder.CreateTruncOrBitCast(IVOper, OperTy, "lsr.chain");
}
Inc.UserInst->replaceUsesOfWith(Inc.IVOperand, IVOper);
DeadInsts.emplace_back(Inc.IVOperand);
}
// If LSR created a new, wider phi, we may also replace its postinc. We only
// do this if we also found a wide value for the head of the chain.
if (isa<PHINode>(Chain.tailUserInst())) {
for (BasicBlock::iterator I = L->getHeader()->begin();
PHINode *Phi = dyn_cast<PHINode>(I); ++I) {
if (!isCompatibleIVType(Phi, IVSrc))
continue;
Instruction *PostIncV = dyn_cast<Instruction>(
Phi->getIncomingValueForBlock(L->getLoopLatch()));
if (!PostIncV || (SE.getSCEV(PostIncV) != SE.getSCEV(IVSrc)))
continue;
Value *IVOper = IVSrc;
Type *PostIncTy = PostIncV->getType();
if (IVTy != PostIncTy) {
assert(PostIncTy->isPointerTy() && "mixing int/ptr IV types");
IRBuilder<> Builder(L->getLoopLatch()->getTerminator());
Builder.SetCurrentDebugLocation(PostIncV->getDebugLoc());
IVOper = Builder.CreatePointerCast(IVSrc, PostIncTy, "lsr.chain");
}
Phi->replaceUsesOfWith(PostIncV, IVOper);
DeadInsts.emplace_back(PostIncV);
}
}
}
void LSRInstance::CollectFixupsAndInitialFormulae() {
for (const IVStrideUse &U : IU) {
Instruction *UserInst = U.getUser();
// Skip IV users that are part of profitable IV Chains.
User::op_iterator UseI =
find(UserInst->operands(), U.getOperandValToReplace());
assert(UseI != UserInst->op_end() && "cannot find IV operand");
if (IVIncSet.count(UseI))
continue;
LSRUse::KindType Kind = LSRUse::Basic;
MemAccessTy AccessTy;
if (isAddressUse(UserInst, U.getOperandValToReplace())) {
Kind = LSRUse::Address;
AccessTy = getAccessType(UserInst);
}
const SCEV *S = IU.getExpr(U);
PostIncLoopSet TmpPostIncLoops = U.getPostIncLoops();
// Equality (== and !=) ICmps are special. We can rewrite (i == N) as
// (N - i == 0), and this allows (N - i) to be the expression that we work
// with rather than just N or i, so we can consider the register
// requirements for both N and i at the same time. Limiting this code to
// equality icmps is not a problem because all interesting loops use
// equality icmps, thanks to IndVarSimplify.
if (ICmpInst *CI = dyn_cast<ICmpInst>(UserInst))
if (CI->isEquality()) {
// Swap the operands if needed to put the OperandValToReplace on the
// left, for consistency.
Value *NV = CI->getOperand(1);
if (NV == U.getOperandValToReplace()) {
CI->setOperand(1, CI->getOperand(0));
CI->setOperand(0, NV);
NV = CI->getOperand(1);
Changed = true;
}
// x == y --> x - y == 0
const SCEV *N = SE.getSCEV(NV);
if (SE.isLoopInvariant(N, L) && isSafeToExpand(N, SE)) {
// S is normalized, so normalize N before folding it into S
// to keep the result normalized.
N = TransformForPostIncUse(Normalize, N, CI, nullptr,
TmpPostIncLoops, SE, DT);
Kind = LSRUse::ICmpZero;
S = SE.getMinusSCEV(N, S);
}
// -1 and the negations of all interesting strides (except the negation
// of -1) are now also interesting.
for (size_t i = 0, e = Factors.size(); i != e; ++i)
if (Factors[i] != -1)
Factors.insert(-(uint64_t)Factors[i]);
Factors.insert(-1);
}
// Get or create an LSRUse.
std::pair<size_t, int64_t> P = getUse(S, Kind, AccessTy);
size_t LUIdx = P.first;
int64_t Offset = P.second;
LSRUse &LU = Uses[LUIdx];
// Record the fixup.
LSRFixup &LF = LU.getNewFixup();
LF.UserInst = UserInst;
LF.OperandValToReplace = U.getOperandValToReplace();
LF.PostIncLoops = TmpPostIncLoops;
LF.Offset = Offset;
LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L);
if (!LU.WidestFixupType ||
SE.getTypeSizeInBits(LU.WidestFixupType) <
SE.getTypeSizeInBits(LF.OperandValToReplace->getType()))
LU.WidestFixupType = LF.OperandValToReplace->getType();
// If this is the first use of this LSRUse, give it a formula.
if (LU.Formulae.empty()) {
InsertInitialFormula(S, LU, LUIdx);
CountRegisters(LU.Formulae.back(), LUIdx);
}
}
DEBUG(print_fixups(dbgs()));
}
/// Insert a formula for the given expression into the given use, separating out
/// loop-variant portions from loop-invariant and loop-computable portions.
void
LSRInstance::InsertInitialFormula(const SCEV *S, LSRUse &LU, size_t LUIdx) {
// Mark uses whose expressions cannot be expanded.
if (!isSafeToExpand(S, SE))
LU.RigidFormula = true;
Formula F;
F.initialMatch(S, L, SE);
bool Inserted = InsertFormula(LU, LUIdx, F);
assert(Inserted && "Initial formula already exists!"); (void)Inserted;
}
/// Insert a simple single-register formula for the given expression into the
/// given use.
void
LSRInstance::InsertSupplementalFormula(const SCEV *S,
LSRUse &LU, size_t LUIdx) {
Formula F;
F.BaseRegs.push_back(S);
F.HasBaseReg = true;
bool Inserted = InsertFormula(LU, LUIdx, F);
assert(Inserted && "Supplemental formula already exists!"); (void)Inserted;
}
/// Note which registers are used by the given formula, updating RegUses.
void LSRInstance::CountRegisters(const Formula &F, size_t LUIdx) {
if (F.ScaledReg)
RegUses.countRegister(F.ScaledReg, LUIdx);
for (const SCEV *BaseReg : F.BaseRegs)
RegUses.countRegister(BaseReg, LUIdx);
}
/// If the given formula has not yet been inserted, add it to the list, and
/// return true. Return false otherwise.
bool LSRInstance::InsertFormula(LSRUse &LU, unsigned LUIdx, const Formula &F) {
// Do not insert formula that we will not be able to expand.
assert(isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F) &&
"Formula is illegal");
if (!LU.InsertFormula(F))
return false;
CountRegisters(F, LUIdx);
return true;
}
/// Check for other uses of loop-invariant values which we're tracking. These
/// other uses will pin these values in registers, making them less profitable
/// for elimination.
/// TODO: This currently misses non-constant addrec step registers.
/// TODO: Should this give more weight to users inside the loop?
void
LSRInstance::CollectLoopInvariantFixupsAndFormulae() {
SmallVector<const SCEV *, 8> Worklist(RegUses.begin(), RegUses.end());
SmallPtrSet<const SCEV *, 32> Visited;
while (!Worklist.empty()) {
const SCEV *S = Worklist.pop_back_val();
// Don't process the same SCEV twice
if (!Visited.insert(S).second)
continue;
if (const SCEVNAryExpr *N = dyn_cast<SCEVNAryExpr>(S))
Worklist.append(N->op_begin(), N->op_end());
else if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
Worklist.push_back(C->getOperand());
else if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) {
Worklist.push_back(D->getLHS());
Worklist.push_back(D->getRHS());
} else if (const SCEVUnknown *US = dyn_cast<SCEVUnknown>(S)) {
const Value *V = US->getValue();
if (const Instruction *Inst = dyn_cast<Instruction>(V)) {
// Look for instructions defined outside the loop.
if (L->contains(Inst)) continue;
} else if (isa<UndefValue>(V))
// Undef doesn't have a live range, so it doesn't matter.
continue;
for (const Use &U : V->uses()) {
const Instruction *UserInst = dyn_cast<Instruction>(U.getUser());
// Ignore non-instructions.
if (!UserInst)
continue;
// Ignore instructions in other functions (as can happen with
// Constants).
if (UserInst->getParent()->getParent() != L->getHeader()->getParent())
continue;
// Ignore instructions not dominated by the loop.
const BasicBlock *UseBB = !isa<PHINode>(UserInst) ?
UserInst->getParent() :
cast<PHINode>(UserInst)->getIncomingBlock(
PHINode::getIncomingValueNumForOperand(U.getOperandNo()));
if (!DT.dominates(L->getHeader(), UseBB))
continue;
// Don't bother if the instruction is in a BB which ends in an EHPad.
if (UseBB->getTerminator()->isEHPad())
continue;
// Ignore uses which are part of other SCEV expressions, to avoid
// analyzing them multiple times.
if (SE.isSCEVable(UserInst->getType())) {
const SCEV *UserS = SE.getSCEV(const_cast<Instruction *>(UserInst));
// If the user is a no-op, look through to its uses.
if (!isa<SCEVUnknown>(UserS))
continue;
if (UserS == US) {
Worklist.push_back(
SE.getUnknown(const_cast<Instruction *>(UserInst)));
continue;
}
}
// Ignore icmp instructions which are already being analyzed.
if (const ICmpInst *ICI = dyn_cast<ICmpInst>(UserInst)) {
unsigned OtherIdx = !U.getOperandNo();
Value *OtherOp = const_cast<Value *>(ICI->getOperand(OtherIdx));
if (SE.hasComputableLoopEvolution(SE.getSCEV(OtherOp), L))
continue;
}
std::pair<size_t, int64_t> P = getUse(
S, LSRUse::Basic, MemAccessTy());
size_t LUIdx = P.first;
int64_t Offset = P.second;
LSRUse &LU = Uses[LUIdx];
LSRFixup &LF = LU.getNewFixup();
LF.UserInst = const_cast<Instruction *>(UserInst);
LF.OperandValToReplace = U;
LF.Offset = Offset;
LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L);
if (!LU.WidestFixupType ||
SE.getTypeSizeInBits(LU.WidestFixupType) <
SE.getTypeSizeInBits(LF.OperandValToReplace->getType()))
LU.WidestFixupType = LF.OperandValToReplace->getType();
InsertSupplementalFormula(US, LU, LUIdx);
CountRegisters(LU.Formulae.back(), Uses.size() - 1);
break;
}
}
}
}
/// Split S into subexpressions which can be pulled out into separate
/// registers. If C is non-null, multiply each subexpression by C.
///
/// Return remainder expression after factoring the subexpressions captured by
/// Ops. If Ops is complete, return NULL.
static const SCEV *CollectSubexprs(const SCEV *S, const SCEVConstant *C,
SmallVectorImpl<const SCEV *> &Ops,
const Loop *L,
ScalarEvolution &SE,
unsigned Depth = 0) {
// Arbitrarily cap recursion to protect compile time.
if (Depth >= 3)
return S;
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
// Break out add operands.
for (const SCEV *S : Add->operands()) {
const SCEV *Remainder = CollectSubexprs(S, C, Ops, L, SE, Depth+1);
if (Remainder)
Ops.push_back(C ? SE.getMulExpr(C, Remainder) : Remainder);
}
return nullptr;
} else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// Split a non-zero base out of an addrec.
if (AR->getStart()->isZero())
return S;
const SCEV *Remainder = CollectSubexprs(AR->getStart(),
C, Ops, L, SE, Depth+1);
// Split the non-zero AddRec unless it is part of a nested recurrence that
// does not pertain to this loop.
if (Remainder && (AR->getLoop() == L || !isa<SCEVAddRecExpr>(Remainder))) {
Ops.push_back(C ? SE.getMulExpr(C, Remainder) : Remainder);
Remainder = nullptr;
}
if (Remainder != AR->getStart()) {
if (!Remainder)
Remainder = SE.getConstant(AR->getType(), 0);
return SE.getAddRecExpr(Remainder,
AR->getStepRecurrence(SE),
AR->getLoop(),
//FIXME: AR->getNoWrapFlags(SCEV::FlagNW)
SCEV::FlagAnyWrap);
}
} else if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
// Break (C * (a + b + c)) into C*a + C*b + C*c.
if (Mul->getNumOperands() != 2)
return S;
if (const SCEVConstant *Op0 =
dyn_cast<SCEVConstant>(Mul->getOperand(0))) {
C = C ? cast<SCEVConstant>(SE.getMulExpr(C, Op0)) : Op0;
const SCEV *Remainder =
CollectSubexprs(Mul->getOperand(1), C, Ops, L, SE, Depth+1);
if (Remainder)
Ops.push_back(SE.getMulExpr(C, Remainder));
return nullptr;
}
}
return S;
}
/// \brief Helper function for LSRInstance::GenerateReassociations.
void LSRInstance::GenerateReassociationsImpl(LSRUse &LU, unsigned LUIdx,
const Formula &Base,
unsigned Depth, size_t Idx,
bool IsScaledReg) {
const SCEV *BaseReg = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx];
SmallVector<const SCEV *, 8> AddOps;
const SCEV *Remainder = CollectSubexprs(BaseReg, nullptr, AddOps, L, SE);
if (Remainder)
AddOps.push_back(Remainder);
if (AddOps.size() == 1)
return;
for (SmallVectorImpl<const SCEV *>::const_iterator J = AddOps.begin(),
JE = AddOps.end();
J != JE; ++J) {
// Loop-variant "unknown" values are uninteresting; we won't be able to
// do anything meaningful with them.
if (isa<SCEVUnknown>(*J) && !SE.isLoopInvariant(*J, L))
continue;
// Don't pull a constant into a register if the constant could be folded
// into an immediate field.
if (isAlwaysFoldable(TTI, SE, LU.MinOffset, LU.MaxOffset, LU.Kind,
LU.AccessTy, *J, Base.getNumRegs() > 1))
continue;
// Collect all operands except *J.
SmallVector<const SCEV *, 8> InnerAddOps(
((const SmallVector<const SCEV *, 8> &)AddOps).begin(), J);
InnerAddOps.append(std::next(J),
((const SmallVector<const SCEV *, 8> &)AddOps).end());
// Don't leave just a constant behind in a register if the constant could
// be folded into an immediate field.
if (InnerAddOps.size() == 1 &&
isAlwaysFoldable(TTI, SE, LU.MinOffset, LU.MaxOffset, LU.Kind,
LU.AccessTy, InnerAddOps[0], Base.getNumRegs() > 1))
continue;
const SCEV *InnerSum = SE.getAddExpr(InnerAddOps);
if (InnerSum->isZero())
continue;
Formula F = Base;
// Add the remaining pieces of the add back into the new formula.
const SCEVConstant *InnerSumSC = dyn_cast<SCEVConstant>(InnerSum);
if (InnerSumSC && SE.getTypeSizeInBits(InnerSumSC->getType()) <= 64 &&
TTI.isLegalAddImmediate((uint64_t)F.UnfoldedOffset +
InnerSumSC->getValue()->getZExtValue())) {
F.UnfoldedOffset =
(uint64_t)F.UnfoldedOffset + InnerSumSC->getValue()->getZExtValue();
if (IsScaledReg)
F.ScaledReg = nullptr;
else
F.BaseRegs.erase(F.BaseRegs.begin() + Idx);
} else if (IsScaledReg)
F.ScaledReg = InnerSum;
else
F.BaseRegs[Idx] = InnerSum;
// Add J as its own register, or an unfolded immediate.
const SCEVConstant *SC = dyn_cast<SCEVConstant>(*J);
if (SC && SE.getTypeSizeInBits(SC->getType()) <= 64 &&
TTI.isLegalAddImmediate((uint64_t)F.UnfoldedOffset +
SC->getValue()->getZExtValue()))
F.UnfoldedOffset =
(uint64_t)F.UnfoldedOffset + SC->getValue()->getZExtValue();
else
F.BaseRegs.push_back(*J);
// We may have changed the number of register in base regs, adjust the
// formula accordingly.
F.canonicalize();
if (InsertFormula(LU, LUIdx, F))
// If that formula hadn't been seen before, recurse to find more like
// it.
GenerateReassociations(LU, LUIdx, LU.Formulae.back(), Depth + 1);
}
}
/// Split out subexpressions from adds and the bases of addrecs.
void LSRInstance::GenerateReassociations(LSRUse &LU, unsigned LUIdx,
Formula Base, unsigned Depth) {
assert(Base.isCanonical() && "Input must be in the canonical form");
// Arbitrarily cap recursion to protect compile time.
if (Depth >= 3)
return;
for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i)
GenerateReassociationsImpl(LU, LUIdx, Base, Depth, i);
if (Base.Scale == 1)
GenerateReassociationsImpl(LU, LUIdx, Base, Depth,
/* Idx */ -1, /* IsScaledReg */ true);
}
/// Generate a formula consisting of all of the loop-dominating registers added
/// into a single register.
void LSRInstance::GenerateCombinations(LSRUse &LU, unsigned LUIdx,
Formula Base) {
// This method is only interesting on a plurality of registers.
if (Base.BaseRegs.size() + (Base.Scale == 1) <= 1)
return;
// Flatten the representation, i.e., reg1 + 1*reg2 => reg1 + reg2, before
// processing the formula.
Base.unscale();
Formula F = Base;
F.BaseRegs.clear();
SmallVector<const SCEV *, 4> Ops;
for (const SCEV *BaseReg : Base.BaseRegs) {
if (SE.properlyDominates(BaseReg, L->getHeader()) &&
!SE.hasComputableLoopEvolution(BaseReg, L))
Ops.push_back(BaseReg);
else
F.BaseRegs.push_back(BaseReg);
}
if (Ops.size() > 1) {
const SCEV *Sum = SE.getAddExpr(Ops);
// TODO: If Sum is zero, it probably means ScalarEvolution missed an
// opportunity to fold something. For now, just ignore such cases
// rather than proceed with zero in a register.
if (!Sum->isZero()) {
F.BaseRegs.push_back(Sum);
F.canonicalize();
(void)InsertFormula(LU, LUIdx, F);
}
}
}
/// \brief Helper function for LSRInstance::GenerateSymbolicOffsets.
void LSRInstance::GenerateSymbolicOffsetsImpl(LSRUse &LU, unsigned LUIdx,
const Formula &Base, size_t Idx,
bool IsScaledReg) {
const SCEV *G = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx];
GlobalValue *GV = ExtractSymbol(G, SE);
if (G->isZero() || !GV)
return;
Formula F = Base;
F.BaseGV = GV;
if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F))
return;
if (IsScaledReg)
F.ScaledReg = G;
else
F.BaseRegs[Idx] = G;
(void)InsertFormula(LU, LUIdx, F);
}
/// Generate reuse formulae using symbolic offsets.
void LSRInstance::GenerateSymbolicOffsets(LSRUse &LU, unsigned LUIdx,
Formula Base) {
// We can't add a symbolic offset if the address already contains one.
if (Base.BaseGV) return;
for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i)
GenerateSymbolicOffsetsImpl(LU, LUIdx, Base, i);
if (Base.Scale == 1)
GenerateSymbolicOffsetsImpl(LU, LUIdx, Base, /* Idx */ -1,
/* IsScaledReg */ true);
}
/// \brief Helper function for LSRInstance::GenerateConstantOffsets.
void LSRInstance::GenerateConstantOffsetsImpl(
LSRUse &LU, unsigned LUIdx, const Formula &Base,
const SmallVectorImpl<int64_t> &Worklist, size_t Idx, bool IsScaledReg) {
const SCEV *G = IsScaledReg ? Base.ScaledReg : Base.BaseRegs[Idx];
for (int64_t Offset : Worklist) {
Formula F = Base;
F.BaseOffset = (uint64_t)Base.BaseOffset - Offset;
if (isLegalUse(TTI, LU.MinOffset - Offset, LU.MaxOffset - Offset, LU.Kind,
LU.AccessTy, F)) {
// Add the offset to the base register.
const SCEV *NewG = SE.getAddExpr(SE.getConstant(G->getType(), Offset), G);
// If it cancelled out, drop the base register, otherwise update it.
if (NewG->isZero()) {
if (IsScaledReg) {
F.Scale = 0;
F.ScaledReg = nullptr;
} else
F.deleteBaseReg(F.BaseRegs[Idx]);
F.canonicalize();
} else if (IsScaledReg)
F.ScaledReg = NewG;
else
F.BaseRegs[Idx] = NewG;
(void)InsertFormula(LU, LUIdx, F);
}
}
int64_t Imm = ExtractImmediate(G, SE);
if (G->isZero() || Imm == 0)
return;
Formula F = Base;
F.BaseOffset = (uint64_t)F.BaseOffset + Imm;
if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy, F))
return;
if (IsScaledReg)
F.ScaledReg = G;
else
F.BaseRegs[Idx] = G;
(void)InsertFormula(LU, LUIdx, F);
}
/// GenerateConstantOffsets - Generate reuse formulae using symbolic offsets.
void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
Formula Base) {
// TODO: For now, just add the min and max offset, because it usually isn't
// worthwhile looking at everything inbetween.
SmallVector<int64_t, 2> Worklist;
Worklist.push_back(LU.MinOffset);
if (LU.MaxOffset != LU.MinOffset)
Worklist.push_back(LU.MaxOffset);
for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i)
GenerateConstantOffsetsImpl(LU, LUIdx, Base, Worklist, i);
if (Base.Scale == 1)
GenerateConstantOffsetsImpl(LU, LUIdx, Base, Worklist, /* Idx */ -1,
/* IsScaledReg */ true);
}
/// For ICmpZero, check to see if we can scale up the comparison. For example, x
/// == y -> x*c == y*c.
void LSRInstance::GenerateICmpZeroScales(LSRUse &LU, unsigned LUIdx,
Formula Base) {
if (LU.Kind != LSRUse::ICmpZero) return;
// Determine the integer type for the base formula.
Type *IntTy = Base.getType();
if (!IntTy) return;
if (SE.getTypeSizeInBits(IntTy) > 64) return;
// Don't do this if there is more than one offset.
if (LU.MinOffset != LU.MaxOffset) return;
assert(!Base.BaseGV && "ICmpZero use is not legal!");
// Check each interesting stride.
for (int64_t Factor : Factors) {
// Check that the multiplication doesn't overflow.
if (Base.BaseOffset == INT64_MIN && Factor == -1)
continue;
int64_t NewBaseOffset = (uint64_t)Base.BaseOffset * Factor;
if (NewBaseOffset / Factor != Base.BaseOffset)
continue;
// If the offset will be truncated at this use, check that it is in bounds.
if (!IntTy->isPointerTy() &&
!ConstantInt::isValueValidForType(IntTy, NewBaseOffset))
continue;
// Check that multiplying with the use offset doesn't overflow.
int64_t Offset = LU.MinOffset;
if (Offset == INT64_MIN && Factor == -1)
continue;
Offset = (uint64_t)Offset * Factor;
if (Offset / Factor != LU.MinOffset)
continue;
// If the offset will be truncated at this use, check that it is in bounds.
if (!IntTy->isPointerTy() &&
!ConstantInt::isValueValidForType(IntTy, Offset))
continue;
Formula F = Base;
F.BaseOffset = NewBaseOffset;
// Check that this scale is legal.
if (!isLegalUse(TTI, Offset, Offset, LU.Kind, LU.AccessTy, F))
continue;
// Compensate for the use having MinOffset built into it.
F.BaseOffset = (uint64_t)F.BaseOffset + Offset - LU.MinOffset;
const SCEV *FactorS = SE.getConstant(IntTy, Factor);
// Check that multiplying with each base register doesn't overflow.
for (size_t i = 0, e = F.BaseRegs.size(); i != e; ++i) {
F.BaseRegs[i] = SE.getMulExpr(F.BaseRegs[i], FactorS);
if (getExactSDiv(F.BaseRegs[i], FactorS, SE) != Base.BaseRegs[i])
goto next;
}
// Check that multiplying with the scaled register doesn't overflow.
if (F.ScaledReg) {
F.ScaledReg = SE.getMulExpr(F.ScaledReg, FactorS);
if (getExactSDiv(F.ScaledReg, FactorS, SE) != Base.ScaledReg)
continue;
}
// Check that multiplying with the unfolded offset doesn't overflow.
if (F.UnfoldedOffset != 0) {
if (F.UnfoldedOffset == INT64_MIN && Factor == -1)
continue;
F.UnfoldedOffset = (uint64_t)F.UnfoldedOffset * Factor;
if (F.UnfoldedOffset / Factor != Base.UnfoldedOffset)
continue;
// If the offset will be truncated, check that it is in bounds.
if (!IntTy->isPointerTy() &&
!ConstantInt::isValueValidForType(IntTy, F.UnfoldedOffset))
continue;
}
// If we make it here and it's legal, add it.
(void)InsertFormula(LU, LUIdx, F);
next:;
}
}
/// Generate stride factor reuse formulae by making use of scaled-offset address
/// modes, for example.
void LSRInstance::GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base) {
// Determine the integer type for the base formula.
Type *IntTy = Base.getType();
if (!IntTy) return;
// If this Formula already has a scaled register, we can't add another one.
// Try to unscale the formula to generate a better scale.
if (Base.Scale != 0 && !Base.unscale())
return;
assert(Base.Scale == 0 && "unscale did not did its job!");
// Check each interesting stride.
for (int64_t Factor : Factors) {
Base.Scale = Factor;
Base.HasBaseReg = Base.BaseRegs.size() > 1;
// Check whether this scale is going to be legal.
if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy,
Base)) {
// As a special-case, handle special out-of-loop Basic users specially.
// TODO: Reconsider this special case.
if (LU.Kind == LSRUse::Basic &&
isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LSRUse::Special,
LU.AccessTy, Base) &&
LU.AllFixupsOutsideLoop)
LU.Kind = LSRUse::Special;
else
continue;
}
// For an ICmpZero, negating a solitary base register won't lead to
// new solutions.
if (LU.Kind == LSRUse::ICmpZero &&
!Base.HasBaseReg && Base.BaseOffset == 0 && !Base.BaseGV)
continue;
// For each addrec base reg, apply the scale, if possible.
for (size_t i = 0, e = Base.BaseRegs.size(); i != e; ++i)
if (const SCEVAddRecExpr *AR =
dyn_cast<SCEVAddRecExpr>(Base.BaseRegs[i])) {
const SCEV *FactorS = SE.getConstant(IntTy, Factor);
if (FactorS->isZero())
continue;
// Divide out the factor, ignoring high bits, since we'll be
// scaling the value back up in the end.
if (const SCEV *Quotient = getExactSDiv(AR, FactorS, SE, true)) {
// TODO: This could be optimized to avoid all the copying.
Formula F = Base;
F.ScaledReg = Quotient;
F.deleteBaseReg(F.BaseRegs[i]);
// The canonical representation of 1*reg is reg, which is already in
// Base. In that case, do not try to insert the formula, it will be
// rejected anyway.
if (F.Scale == 1 && F.BaseRegs.empty())
continue;
(void)InsertFormula(LU, LUIdx, F);
}
}
}
}
/// Generate reuse formulae from different IV types.
void LSRInstance::GenerateTruncates(LSRUse &LU, unsigned LUIdx, Formula Base) {
// Don't bother truncating symbolic values.
if (Base.BaseGV) return;
// Determine the integer type for the base formula.
Type *DstTy = Base.getType();
if (!DstTy) return;
DstTy = SE.getEffectiveSCEVType(DstTy);
for (Type *SrcTy : Types) {
if (SrcTy != DstTy && TTI.isTruncateFree(SrcTy, DstTy)) {
Formula F = Base;
if (F.ScaledReg) F.ScaledReg = SE.getAnyExtendExpr(F.ScaledReg, SrcTy);
for (const SCEV *&BaseReg : F.BaseRegs)
BaseReg = SE.getAnyExtendExpr(BaseReg, SrcTy);
// TODO: This assumes we've done basic processing on all uses and
// have an idea what the register usage is.
if (!F.hasRegsUsedByUsesOtherThan(LUIdx, RegUses))
continue;
(void)InsertFormula(LU, LUIdx, F);
}
}
}
namespace {
/// Helper class for GenerateCrossUseConstantOffsets. It's used to defer
/// modifications so that the search phase doesn't have to worry about the data
/// structures moving underneath it.
struct WorkItem {
size_t LUIdx;
int64_t Imm;
const SCEV *OrigReg;
WorkItem(size_t LI, int64_t I, const SCEV *R)
: LUIdx(LI), Imm(I), OrigReg(R) {}
void print(raw_ostream &OS) const;
void dump() const;
};
}
void WorkItem::print(raw_ostream &OS) const {
OS << "in formulae referencing " << *OrigReg << " in use " << LUIdx
<< " , add offset " << Imm;
}
LLVM_DUMP_METHOD
void WorkItem::dump() const {
print(errs()); errs() << '\n';
}
/// Look for registers which are a constant distance apart and try to form reuse
/// opportunities between them.
void LSRInstance::GenerateCrossUseConstantOffsets() {
// Group the registers by their value without any added constant offset.
typedef std::map<int64_t, const SCEV *> ImmMapTy;
DenseMap<const SCEV *, ImmMapTy> Map;
DenseMap<const SCEV *, SmallBitVector> UsedByIndicesMap;
SmallVector<const SCEV *, 8> Sequence;
for (const SCEV *Use : RegUses) {
const SCEV *Reg = Use; // Make a copy for ExtractImmediate to modify.
int64_t Imm = ExtractImmediate(Reg, SE);
auto Pair = Map.insert(std::make_pair(Reg, ImmMapTy()));
if (Pair.second)
Sequence.push_back(Reg);
Pair.first->second.insert(std::make_pair(Imm, Use));
UsedByIndicesMap[Reg] |= RegUses.getUsedByIndices(Use);
}
// Now examine each set of registers with the same base value. Build up
// a list of work to do and do the work in a separate step so that we're
// not adding formulae and register counts while we're searching.
SmallVector<WorkItem, 32> WorkItems;
SmallSet<std::pair<size_t, int64_t>, 32> UniqueItems;
for (const SCEV *Reg : Sequence) {
const ImmMapTy &Imms = Map.find(Reg)->second;
// It's not worthwhile looking for reuse if there's only one offset.
if (Imms.size() == 1)
continue;
DEBUG(dbgs() << "Generating cross-use offsets for " << *Reg << ':';
for (const auto &Entry : Imms)
dbgs() << ' ' << Entry.first;
dbgs() << '\n');
// Examine each offset.
for (ImmMapTy::const_iterator J = Imms.begin(), JE = Imms.end();
J != JE; ++J) {
const SCEV *OrigReg = J->second;
int64_t JImm = J->first;
const SmallBitVector &UsedByIndices = RegUses.getUsedByIndices(OrigReg);
if (!isa<SCEVConstant>(OrigReg) &&
UsedByIndicesMap[Reg].count() == 1) {
DEBUG(dbgs() << "Skipping cross-use reuse for " << *OrigReg << '\n');
continue;
}
// Conservatively examine offsets between this orig reg a few selected
// other orig regs.
ImmMapTy::const_iterator OtherImms[] = {
Imms.begin(), std::prev(Imms.end()),
Imms.lower_bound((Imms.begin()->first + std::prev(Imms.end())->first) /
2)
};
for (size_t i = 0, e = array_lengthof(OtherImms); i != e; ++i) {
ImmMapTy::const_iterator M = OtherImms[i];
if (M == J || M == JE) continue;
// Compute the difference between the two.
int64_t Imm = (uint64_t)JImm - M->first;
for (int LUIdx = UsedByIndices.find_first(); LUIdx != -1;
LUIdx = UsedByIndices.find_next(LUIdx))
// Make a memo of this use, offset, and register tuple.
if (UniqueItems.insert(std::make_pair(LUIdx, Imm)).second)
WorkItems.push_back(WorkItem(LUIdx, Imm, OrigReg));
}
}
}
Map.clear();
Sequence.clear();
UsedByIndicesMap.clear();
UniqueItems.clear();
// Now iterate through the worklist and add new formulae.
for (const WorkItem &WI : WorkItems) {
size_t LUIdx = WI.LUIdx;
LSRUse &LU = Uses[LUIdx];
int64_t Imm = WI.Imm;
const SCEV *OrigReg = WI.OrigReg;
Type *IntTy = SE.getEffectiveSCEVType(OrigReg->getType());
const SCEV *NegImmS = SE.getSCEV(ConstantInt::get(IntTy, -(uint64_t)Imm));
unsigned BitWidth = SE.getTypeSizeInBits(IntTy);
// TODO: Use a more targeted data structure.
for (size_t L = 0, LE = LU.Formulae.size(); L != LE; ++L) {
Formula F = LU.Formulae[L];
// FIXME: The code for the scaled and unscaled registers looks
// very similar but slightly different. Investigate if they
// could be merged. That way, we would not have to unscale the
// Formula.
F.unscale();
// Use the immediate in the scaled register.
if (F.ScaledReg == OrigReg) {
int64_t Offset = (uint64_t)F.BaseOffset + Imm * (uint64_t)F.Scale;
// Don't create 50 + reg(-50).
if (F.referencesReg(SE.getSCEV(
ConstantInt::get(IntTy, -(uint64_t)Offset))))
continue;
Formula NewF = F;
NewF.BaseOffset = Offset;
if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy,
NewF))
continue;
NewF.ScaledReg = SE.getAddExpr(NegImmS, NewF.ScaledReg);
// If the new scale is a constant in a register, and adding the constant
// value to the immediate would produce a value closer to zero than the
// immediate itself, then the formula isn't worthwhile.
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(NewF.ScaledReg))
if (C->getValue()->isNegative() != (NewF.BaseOffset < 0) &&
(C->getAPInt().abs() * APInt(BitWidth, F.Scale))
.ule(std::abs(NewF.BaseOffset)))
continue;
// OK, looks good.
NewF.canonicalize();
(void)InsertFormula(LU, LUIdx, NewF);
} else {
// Use the immediate in a base register.
for (size_t N = 0, NE = F.BaseRegs.size(); N != NE; ++N) {
const SCEV *BaseReg = F.BaseRegs[N];
if (BaseReg != OrigReg)
continue;
Formula NewF = F;
NewF.BaseOffset = (uint64_t)NewF.BaseOffset + Imm;
if (!isLegalUse(TTI, LU.MinOffset, LU.MaxOffset,
LU.Kind, LU.AccessTy, NewF)) {
if (!TTI.isLegalAddImmediate((uint64_t)NewF.UnfoldedOffset + Imm))
continue;
NewF = F;
NewF.UnfoldedOffset = (uint64_t)NewF.UnfoldedOffset + Imm;
}
NewF.BaseRegs[N] = SE.getAddExpr(NegImmS, BaseReg);
// If the new formula has a constant in a register, and adding the
// constant value to the immediate would produce a value closer to
// zero than the immediate itself, then the formula isn't worthwhile.
for (const SCEV *NewReg : NewF.BaseRegs)
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(NewReg))
if ((C->getAPInt() + NewF.BaseOffset)
.abs()
.slt(std::abs(NewF.BaseOffset)) &&
(C->getAPInt() + NewF.BaseOffset).countTrailingZeros() >=
countTrailingZeros<uint64_t>(NewF.BaseOffset))
goto skip_formula;
// Ok, looks good.
NewF.canonicalize();
(void)InsertFormula(LU, LUIdx, NewF);
break;
skip_formula:;
}
}
}
}
}
/// Generate formulae for each use.
void
LSRInstance::GenerateAllReuseFormulae() {
// This is split into multiple loops so that hasRegsUsedByUsesOtherThan
// queries are more precise.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateReassociations(LU, LUIdx, LU.Formulae[i]);
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateCombinations(LU, LUIdx, LU.Formulae[i]);
}
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateSymbolicOffsets(LU, LUIdx, LU.Formulae[i]);
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateConstantOffsets(LU, LUIdx, LU.Formulae[i]);
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateICmpZeroScales(LU, LUIdx, LU.Formulae[i]);
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateScales(LU, LUIdx, LU.Formulae[i]);
}
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
for (size_t i = 0, f = LU.Formulae.size(); i != f; ++i)
GenerateTruncates(LU, LUIdx, LU.Formulae[i]);
}
GenerateCrossUseConstantOffsets();
DEBUG(dbgs() << "\n"
"After generating reuse formulae:\n";
print_uses(dbgs()));
}
/// If there are multiple formulae with the same set of registers used
/// by other uses, pick the best one and delete the others.
void LSRInstance::FilterOutUndesirableDedicatedRegisters() {
DenseSet<const SCEV *> VisitedRegs;
SmallPtrSet<const SCEV *, 16> Regs;
SmallPtrSet<const SCEV *, 16> LoserRegs;
#ifndef NDEBUG
bool ChangedFormulae = false;
#endif
// Collect the best formula for each unique set of shared registers. This
// is reset for each use.
typedef DenseMap<SmallVector<const SCEV *, 4>, size_t, UniquifierDenseMapInfo>
BestFormulaeTy;
BestFormulaeTy BestFormulae;
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
DEBUG(dbgs() << "Filtering for use "; LU.print(dbgs()); dbgs() << '\n');
bool Any = false;
for (size_t FIdx = 0, NumForms = LU.Formulae.size();
FIdx != NumForms; ++FIdx) {
Formula &F = LU.Formulae[FIdx];
// Some formulas are instant losers. For example, they may depend on
// nonexistent AddRecs from other loops. These need to be filtered
// immediately, otherwise heuristics could choose them over others leading
// to an unsatisfactory solution. Passing LoserRegs into RateFormula here
// avoids the need to recompute this information across formulae using the
// same bad AddRec. Passing LoserRegs is also essential unless we remove
// the corresponding bad register from the Regs set.
Cost CostF;
Regs.clear();
CostF.RateFormula(TTI, F, Regs, VisitedRegs, L, SE, DT, LU, &LoserRegs);
if (CostF.isLoser()) {
// During initial formula generation, undesirable formulae are generated
// by uses within other loops that have some non-trivial address mode or
// use the postinc form of the IV. LSR needs to provide these formulae
// as the basis of rediscovering the desired formula that uses an AddRec
// corresponding to the existing phi. Once all formulae have been
// generated, these initial losers may be pruned.
DEBUG(dbgs() << " Filtering loser "; F.print(dbgs());
dbgs() << "\n");
}
else {
SmallVector<const SCEV *, 4> Key;
for (const SCEV *Reg : F.BaseRegs) {
if (RegUses.isRegUsedByUsesOtherThan(Reg, LUIdx))
Key.push_back(Reg);
}
if (F.ScaledReg &&
RegUses.isRegUsedByUsesOtherThan(F.ScaledReg, LUIdx))
Key.push_back(F.ScaledReg);
// Unstable sort by host order ok, because this is only used for
// uniquifying.
std::sort(Key.begin(), Key.end());
std::pair<BestFormulaeTy::const_iterator, bool> P =
BestFormulae.insert(std::make_pair(Key, FIdx));
if (P.second)
continue;
Formula &Best = LU.Formulae[P.first->second];
Cost CostBest;
Regs.clear();
CostBest.RateFormula(TTI, Best, Regs, VisitedRegs, L, SE, DT, LU);
if (CostF < CostBest)
std::swap(F, Best);
DEBUG(dbgs() << " Filtering out formula "; F.print(dbgs());
dbgs() << "\n"
" in favor of formula "; Best.print(dbgs());
dbgs() << '\n');
}
#ifndef NDEBUG
ChangedFormulae = true;
#endif
LU.DeleteFormula(F);
--FIdx;
--NumForms;
Any = true;
}
// Now that we've filtered out some formulae, recompute the Regs set.
if (Any)
LU.RecomputeRegs(LUIdx, RegUses);
// Reset this to prepare for the next use.
BestFormulae.clear();
}
DEBUG(if (ChangedFormulae) {
dbgs() << "\n"
"After filtering out undesirable candidates:\n";
print_uses(dbgs());
});
}
// This is a rough guess that seems to work fairly well.
static const size_t ComplexityLimit = UINT16_MAX;
/// Estimate the worst-case number of solutions the solver might have to
/// consider. It almost never considers this many solutions because it prune the
/// search space, but the pruning isn't always sufficient.
size_t LSRInstance::EstimateSearchSpaceComplexity() const {
size_t Power = 1;
for (const LSRUse &LU : Uses) {
size_t FSize = LU.Formulae.size();
if (FSize >= ComplexityLimit) {
Power = ComplexityLimit;
break;
}
Power *= FSize;
if (Power >= ComplexityLimit)
break;
}
return Power;
}
/// When one formula uses a superset of the registers of another formula, it
/// won't help reduce register pressure (though it may not necessarily hurt
/// register pressure); remove it to simplify the system.
void LSRInstance::NarrowSearchSpaceByDetectingSupersets() {
if (EstimateSearchSpaceComplexity() >= ComplexityLimit) {
DEBUG(dbgs() << "The search space is too complex.\n");
DEBUG(dbgs() << "Narrowing the search space by eliminating formulae "
"which use a superset of registers used by other "
"formulae.\n");
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
bool Any = false;
for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) {
Formula &F = LU.Formulae[i];
// Look for a formula with a constant or GV in a register. If the use
// also has a formula with that same value in an immediate field,
// delete the one that uses a register.
for (SmallVectorImpl<const SCEV *>::const_iterator
I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) {
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*I)) {
Formula NewF = F;
NewF.BaseOffset += C->getValue()->getSExtValue();
NewF.BaseRegs.erase(NewF.BaseRegs.begin() +
(I - F.BaseRegs.begin()));
if (LU.HasFormulaWithSameRegs(NewF)) {
DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n');
LU.DeleteFormula(F);
--i;
--e;
Any = true;
break;
}
} else if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(*I)) {
if (GlobalValue *GV = dyn_cast<GlobalValue>(U->getValue()))
if (!F.BaseGV) {
Formula NewF = F;
NewF.BaseGV = GV;
NewF.BaseRegs.erase(NewF.BaseRegs.begin() +
(I - F.BaseRegs.begin()));
if (LU.HasFormulaWithSameRegs(NewF)) {
DEBUG(dbgs() << " Deleting "; F.print(dbgs());
dbgs() << '\n');
LU.DeleteFormula(F);
--i;
--e;
Any = true;
break;
}
}
}
}
}
if (Any)
LU.RecomputeRegs(LUIdx, RegUses);
}
DEBUG(dbgs() << "After pre-selection:\n";
print_uses(dbgs()));
}
}
/// When there are many registers for expressions like A, A+1, A+2, etc.,
/// allocate a single register for them.
void LSRInstance::NarrowSearchSpaceByCollapsingUnrolledCode() {
if (EstimateSearchSpaceComplexity() < ComplexityLimit)
return;
DEBUG(dbgs() << "The search space is too complex.\n"
"Narrowing the search space by assuming that uses separated "
"by a constant offset will use the same registers.\n");
// This is especially useful for unrolled loops.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
for (const Formula &F : LU.Formulae) {
if (F.BaseOffset == 0 || (F.Scale != 0 && F.Scale != 1))
continue;
LSRUse *LUThatHas = FindUseWithSimilarFormula(F, LU);
if (!LUThatHas)
continue;
if (!reconcileNewOffset(*LUThatHas, F.BaseOffset, /*HasBaseReg=*/ false,
LU.Kind, LU.AccessTy))
continue;
DEBUG(dbgs() << " Deleting use "; LU.print(dbgs()); dbgs() << '\n');
LUThatHas->AllFixupsOutsideLoop &= LU.AllFixupsOutsideLoop;
// Transfer the fixups of LU to LUThatHas.
for (LSRFixup &Fixup : LU.Fixups) {
Fixup.Offset += F.BaseOffset;
LUThatHas->pushFixup(Fixup);
DEBUG(dbgs() << "New fixup has offset " << Fixup.Offset << '\n');
}
// Delete formulae from the new use which are no longer legal.
bool Any = false;
for (size_t i = 0, e = LUThatHas->Formulae.size(); i != e; ++i) {
Formula &F = LUThatHas->Formulae[i];
if (!isLegalUse(TTI, LUThatHas->MinOffset, LUThatHas->MaxOffset,
LUThatHas->Kind, LUThatHas->AccessTy, F)) {
DEBUG(dbgs() << " Deleting "; F.print(dbgs());
dbgs() << '\n');
LUThatHas->DeleteFormula(F);
--i;
--e;
Any = true;
}
}
if (Any)
LUThatHas->RecomputeRegs(LUThatHas - &Uses.front(), RegUses);
// Delete the old use.
DeleteUse(LU, LUIdx);
--LUIdx;
--NumUses;
break;
}
}
DEBUG(dbgs() << "After pre-selection:\n"; print_uses(dbgs()));
}
/// Call FilterOutUndesirableDedicatedRegisters again, if necessary, now that
/// we've done more filtering, as it may be able to find more formulae to
/// eliminate.
void LSRInstance::NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters(){
if (EstimateSearchSpaceComplexity() >= ComplexityLimit) {
DEBUG(dbgs() << "The search space is too complex.\n");
DEBUG(dbgs() << "Narrowing the search space by re-filtering out "
"undesirable dedicated registers.\n");
FilterOutUndesirableDedicatedRegisters();
DEBUG(dbgs() << "After pre-selection:\n";
print_uses(dbgs()));
}
}
/// Pick a register which seems likely to be profitable, and then in any use
/// which has any reference to that register, delete all formulae which do not
/// reference that register.
void LSRInstance::NarrowSearchSpaceByPickingWinnerRegs() {
// With all other options exhausted, loop until the system is simple
// enough to handle.
SmallPtrSet<const SCEV *, 4> Taken;
while (EstimateSearchSpaceComplexity() >= ComplexityLimit) {
// Ok, we have too many of formulae on our hands to conveniently handle.
// Use a rough heuristic to thin out the list.
DEBUG(dbgs() << "The search space is too complex.\n");
// Pick the register which is used by the most LSRUses, which is likely
// to be a good reuse register candidate.
const SCEV *Best = nullptr;
unsigned BestNum = 0;
for (const SCEV *Reg : RegUses) {
if (Taken.count(Reg))
continue;
if (!Best)
Best = Reg;
else {
unsigned Count = RegUses.getUsedByIndices(Reg).count();
if (Count > BestNum) {
Best = Reg;
BestNum = Count;
}
}
}
DEBUG(dbgs() << "Narrowing the search space by assuming " << *Best
<< " will yield profitable reuse.\n");
Taken.insert(Best);
// In any use with formulae which references this register, delete formulae
// which don't reference it.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
LSRUse &LU = Uses[LUIdx];
if (!LU.Regs.count(Best)) continue;
bool Any = false;
for (size_t i = 0, e = LU.Formulae.size(); i != e; ++i) {
Formula &F = LU.Formulae[i];
if (!F.referencesReg(Best)) {
DEBUG(dbgs() << " Deleting "; F.print(dbgs()); dbgs() << '\n');
LU.DeleteFormula(F);
--e;
--i;
Any = true;
assert(e != 0 && "Use has no formulae left! Is Regs inconsistent?");
continue;
}
}
if (Any)
LU.RecomputeRegs(LUIdx, RegUses);
}
DEBUG(dbgs() << "After pre-selection:\n";
print_uses(dbgs()));
}
}
/// If there are an extraordinary number of formulae to choose from, use some
/// rough heuristics to prune down the number of formulae. This keeps the main
/// solver from taking an extraordinary amount of time in some worst-case
/// scenarios.
void LSRInstance::NarrowSearchSpaceUsingHeuristics() {
NarrowSearchSpaceByDetectingSupersets();
NarrowSearchSpaceByCollapsingUnrolledCode();
NarrowSearchSpaceByRefilteringUndesirableDedicatedRegisters();
NarrowSearchSpaceByPickingWinnerRegs();
}
/// This is the recursive solver.
void LSRInstance::SolveRecurse(SmallVectorImpl<const Formula *> &Solution,
Cost &SolutionCost,
SmallVectorImpl<const Formula *> &Workspace,
const Cost &CurCost,
const SmallPtrSet<const SCEV *, 16> &CurRegs,
DenseSet<const SCEV *> &VisitedRegs) const {
// Some ideas:
// - prune more:
// - use more aggressive filtering
// - sort the formula so that the most profitable solutions are found first
// - sort the uses too
// - search faster:
// - don't compute a cost, and then compare. compare while computing a cost
// and bail early.
// - track register sets with SmallBitVector
const LSRUse &LU = Uses[Workspace.size()];
// If this use references any register that's already a part of the
// in-progress solution, consider it a requirement that a formula must
// reference that register in order to be considered. This prunes out
// unprofitable searching.
SmallSetVector<const SCEV *, 4> ReqRegs;
for (const SCEV *S : CurRegs)
if (LU.Regs.count(S))
ReqRegs.insert(S);
SmallPtrSet<const SCEV *, 16> NewRegs;
Cost NewCost;
for (const Formula &F : LU.Formulae) {
// Ignore formulae which may not be ideal in terms of register reuse of
// ReqRegs. The formula should use all required registers before
// introducing new ones.
int NumReqRegsToFind = std::min(F.getNumRegs(), ReqRegs.size());
for (const SCEV *Reg : ReqRegs) {
if ((F.ScaledReg && F.ScaledReg == Reg) ||
is_contained(F.BaseRegs, Reg)) {
--NumReqRegsToFind;
if (NumReqRegsToFind == 0)
break;
}
}
if (NumReqRegsToFind != 0) {
// If none of the formulae satisfied the required registers, then we could
// clear ReqRegs and try again. Currently, we simply give up in this case.
continue;
}
// Evaluate the cost of the current formula. If it's already worse than
// the current best, prune the search at that point.
NewCost = CurCost;
NewRegs = CurRegs;
NewCost.RateFormula(TTI, F, NewRegs, VisitedRegs, L, SE, DT, LU);
if (NewCost < SolutionCost) {
Workspace.push_back(&F);
if (Workspace.size() != Uses.size()) {
SolveRecurse(Solution, SolutionCost, Workspace, NewCost,
NewRegs, VisitedRegs);
if (F.getNumRegs() == 1 && Workspace.size() == 1)
VisitedRegs.insert(F.ScaledReg ? F.ScaledReg : F.BaseRegs[0]);
} else {
DEBUG(dbgs() << "New best at "; NewCost.print(dbgs());
dbgs() << ".\n Regs:";
for (const SCEV *S : NewRegs)
dbgs() << ' ' << *S;
dbgs() << '\n');
SolutionCost = NewCost;
Solution = Workspace;
}
Workspace.pop_back();
}
}
}
/// Choose one formula from each use. Return the results in the given Solution
/// vector.
void LSRInstance::Solve(SmallVectorImpl<const Formula *> &Solution) const {
SmallVector<const Formula *, 8> Workspace;
Cost SolutionCost;
SolutionCost.Lose();
Cost CurCost;
SmallPtrSet<const SCEV *, 16> CurRegs;
DenseSet<const SCEV *> VisitedRegs;
Workspace.reserve(Uses.size());
// SolveRecurse does all the work.
SolveRecurse(Solution, SolutionCost, Workspace, CurCost,
CurRegs, VisitedRegs);
if (Solution.empty()) {
DEBUG(dbgs() << "\nNo Satisfactory Solution\n");
return;
}
// Ok, we've now made all our decisions.
DEBUG(dbgs() << "\n"
"The chosen solution requires "; SolutionCost.print(dbgs());
dbgs() << ":\n";
for (size_t i = 0, e = Uses.size(); i != e; ++i) {
dbgs() << " ";
Uses[i].print(dbgs());
dbgs() << "\n"
" ";
Solution[i]->print(dbgs());
dbgs() << '\n';
});
assert(Solution.size() == Uses.size() && "Malformed solution!");
}
/// Helper for AdjustInsertPositionForExpand. Climb up the dominator tree far as
/// we can go while still being dominated by the input positions. This helps
/// canonicalize the insert position, which encourages sharing.
BasicBlock::iterator
LSRInstance::HoistInsertPosition(BasicBlock::iterator IP,
const SmallVectorImpl<Instruction *> &Inputs)
const {
Instruction *Tentative = &*IP;
for (;;) {
bool AllDominate = true;
Instruction *BetterPos = nullptr;
// Don't bother attempting to insert before a catchswitch, their basic block
// cannot have other non-PHI instructions.
if (isa<CatchSwitchInst>(Tentative))
return IP;
for (Instruction *Inst : Inputs) {
if (Inst == Tentative || !DT.dominates(Inst, Tentative)) {
AllDominate = false;
break;
}
// Attempt to find an insert position in the middle of the block,
// instead of at the end, so that it can be used for other expansions.
if (Tentative->getParent() == Inst->getParent() &&
(!BetterPos || !DT.dominates(Inst, BetterPos)))
BetterPos = &*std::next(BasicBlock::iterator(Inst));
}
if (!AllDominate)
break;
if (BetterPos)
IP = BetterPos->getIterator();
else
IP = Tentative->getIterator();
const Loop *IPLoop = LI.getLoopFor(IP->getParent());
unsigned IPLoopDepth = IPLoop ? IPLoop->getLoopDepth() : 0;
BasicBlock *IDom;
for (DomTreeNode *Rung = DT.getNode(IP->getParent()); ; ) {
if (!Rung) return IP;
Rung = Rung->getIDom();
if (!Rung) return IP;
IDom = Rung->getBlock();
// Don't climb into a loop though.
const Loop *IDomLoop = LI.getLoopFor(IDom);
unsigned IDomDepth = IDomLoop ? IDomLoop->getLoopDepth() : 0;
if (IDomDepth <= IPLoopDepth &&
(IDomDepth != IPLoopDepth || IDomLoop == IPLoop))
break;
}
Tentative = IDom->getTerminator();
}
return IP;
}
/// Determine an input position which will be dominated by the operands and
/// which will dominate the result.
BasicBlock::iterator
LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator LowestIP,
const LSRFixup &LF,
const LSRUse &LU,
SCEVExpander &Rewriter) const {
// Collect some instructions which must be dominated by the
// expanding replacement. These must be dominated by any operands that
// will be required in the expansion.
SmallVector<Instruction *, 4> Inputs;
if (Instruction *I = dyn_cast<Instruction>(LF.OperandValToReplace))
Inputs.push_back(I);
if (LU.Kind == LSRUse::ICmpZero)
if (Instruction *I =
dyn_cast<Instruction>(cast<ICmpInst>(LF.UserInst)->getOperand(1)))
Inputs.push_back(I);
if (LF.PostIncLoops.count(L)) {
if (LF.isUseFullyOutsideLoop(L))
Inputs.push_back(L->getLoopLatch()->getTerminator());
else
Inputs.push_back(IVIncInsertPos);
}
// The expansion must also be dominated by the increment positions of any
// loops it for which it is using post-inc mode.
for (const Loop *PIL : LF.PostIncLoops) {
if (PIL == L) continue;
// Be dominated by the loop exit.
SmallVector<BasicBlock *, 4> ExitingBlocks;
PIL->getExitingBlocks(ExitingBlocks);
if (!ExitingBlocks.empty()) {
BasicBlock *BB = ExitingBlocks[0];
for (unsigned i = 1, e = ExitingBlocks.size(); i != e; ++i)
BB = DT.findNearestCommonDominator(BB, ExitingBlocks[i]);
Inputs.push_back(BB->getTerminator());
}
}
assert(!isa<PHINode>(LowestIP) && !LowestIP->isEHPad()
&& !isa<DbgInfoIntrinsic>(LowestIP) &&
"Insertion point must be a normal instruction");
// Then, climb up the immediate dominator tree as far as we can go while
// still being dominated by the input positions.
BasicBlock::iterator IP = HoistInsertPosition(LowestIP, Inputs);
// Don't insert instructions before PHI nodes.
while (isa<PHINode>(IP)) ++IP;
// Ignore landingpad instructions.
while (IP->isEHPad()) ++IP;
// Ignore debug intrinsics.
while (isa<DbgInfoIntrinsic>(IP)) ++IP;
// Set IP below instructions recently inserted by SCEVExpander. This keeps the
// IP consistent across expansions and allows the previously inserted
// instructions to be reused by subsequent expansion.
while (Rewriter.isInsertedInstruction(&*IP) && IP != LowestIP)
++IP;
return IP;
}
/// Emit instructions for the leading candidate expression for this LSRUse (this
/// is called "expanding").
Value *LSRInstance::Expand(const LSRUse &LU,
const LSRFixup &LF,
const Formula &F,
BasicBlock::iterator IP,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const {
if (LU.RigidFormula)
return LF.OperandValToReplace;
// Determine an input position which will be dominated by the operands and
// which will dominate the result.
IP = AdjustInsertPositionForExpand(IP, LF, LU, Rewriter);
Rewriter.setInsertPoint(&*IP);
// Inform the Rewriter if we have a post-increment use, so that it can
// perform an advantageous expansion.
Rewriter.setPostInc(LF.PostIncLoops);
// This is the type that the user actually needs.
Type *OpTy = LF.OperandValToReplace->getType();
// This will be the type that we'll initially expand to.
Type *Ty = F.getType();
if (!Ty)
// No type known; just expand directly to the ultimate type.
Ty = OpTy;
else if (SE.getEffectiveSCEVType(Ty) == SE.getEffectiveSCEVType(OpTy))
// Expand directly to the ultimate type if it's the right size.
Ty = OpTy;
// This is the type to do integer arithmetic in.
Type *IntTy = SE.getEffectiveSCEVType(Ty);
// Build up a list of operands to add together to form the full base.
SmallVector<const SCEV *, 8> Ops;
// Expand the BaseRegs portion.
for (const SCEV *Reg : F.BaseRegs) {
assert(!Reg->isZero() && "Zero allocated in a base register!");
// If we're expanding for a post-inc user, make the post-inc adjustment.
PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(LF.PostIncLoops);
Reg = TransformForPostIncUse(Denormalize, Reg,
LF.UserInst, LF.OperandValToReplace,
Loops, SE, DT);
Ops.push_back(SE.getUnknown(Rewriter.expandCodeFor(Reg, nullptr)));
}
// Expand the ScaledReg portion.
Value *ICmpScaledV = nullptr;
if (F.Scale != 0) {
const SCEV *ScaledS = F.ScaledReg;
// If we're expanding for a post-inc user, make the post-inc adjustment.
PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(LF.PostIncLoops);
ScaledS = TransformForPostIncUse(Denormalize, ScaledS,
LF.UserInst, LF.OperandValToReplace,
Loops, SE, DT);
if (LU.Kind == LSRUse::ICmpZero) {
// Expand ScaleReg as if it was part of the base regs.
if (F.Scale == 1)
Ops.push_back(
SE.getUnknown(Rewriter.expandCodeFor(ScaledS, nullptr)));
else {
// An interesting way of "folding" with an icmp is to use a negated
// scale, which we'll implement by inserting it into the other operand
// of the icmp.
assert(F.Scale == -1 &&
"The only scale supported by ICmpZero uses is -1!");
ICmpScaledV = Rewriter.expandCodeFor(ScaledS, nullptr);
}
} else {
// Otherwise just expand the scaled register and an explicit scale,
// which is expected to be matched as part of the address.
// Flush the operand list to suppress SCEVExpander hoisting address modes.
// Unless the addressing mode will not be folded.
if (!Ops.empty() && LU.Kind == LSRUse::Address &&
isAMCompletelyFolded(TTI, LU, F)) {
Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty);
Ops.clear();
Ops.push_back(SE.getUnknown(FullV));
}
ScaledS = SE.getUnknown(Rewriter.expandCodeFor(ScaledS, nullptr));
if (F.Scale != 1)
ScaledS =
SE.getMulExpr(ScaledS, SE.getConstant(ScaledS->getType(), F.Scale));
Ops.push_back(ScaledS);
}
}
// Expand the GV portion.
if (F.BaseGV) {
// Flush the operand list to suppress SCEVExpander hoisting.
if (!Ops.empty()) {
Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty);
Ops.clear();
Ops.push_back(SE.getUnknown(FullV));
}
Ops.push_back(SE.getUnknown(F.BaseGV));
}
// Flush the operand list to suppress SCEVExpander hoisting of both folded and
// unfolded offsets. LSR assumes they both live next to their uses.
if (!Ops.empty()) {
Value *FullV = Rewriter.expandCodeFor(SE.getAddExpr(Ops), Ty);
Ops.clear();
Ops.push_back(SE.getUnknown(FullV));
}
// Expand the immediate portion.
int64_t Offset = (uint64_t)F.BaseOffset + LF.Offset;
if (Offset != 0) {
if (LU.Kind == LSRUse::ICmpZero) {
// The other interesting way of "folding" with an ICmpZero is to use a
// negated immediate.
if (!ICmpScaledV)
ICmpScaledV = ConstantInt::get(IntTy, -(uint64_t)Offset);
else {
Ops.push_back(SE.getUnknown(ICmpScaledV));
ICmpScaledV = ConstantInt::get(IntTy, Offset);
}
} else {
// Just add the immediate values. These again are expected to be matched
// as part of the address.
Ops.push_back(SE.getUnknown(ConstantInt::getSigned(IntTy, Offset)));
}
}
// Expand the unfolded offset portion.
int64_t UnfoldedOffset = F.UnfoldedOffset;
if (UnfoldedOffset != 0) {
// Just add the immediate values.
Ops.push_back(SE.getUnknown(ConstantInt::getSigned(IntTy,
UnfoldedOffset)));
}
// Emit instructions summing all the operands.
const SCEV *FullS = Ops.empty() ?
SE.getConstant(IntTy, 0) :
SE.getAddExpr(Ops);
Value *FullV = Rewriter.expandCodeFor(FullS, Ty);
// We're done expanding now, so reset the rewriter.
Rewriter.clearPostInc();
// An ICmpZero Formula represents an ICmp which we're handling as a
// comparison against zero. Now that we've expanded an expression for that
// form, update the ICmp's other operand.
if (LU.Kind == LSRUse::ICmpZero) {
ICmpInst *CI = cast<ICmpInst>(LF.UserInst);
DeadInsts.emplace_back(CI->getOperand(1));
assert(!F.BaseGV && "ICmp does not support folding a global value and "
"a scale at the same time!");
if (F.Scale == -1) {
if (ICmpScaledV->getType() != OpTy) {
Instruction *Cast =
CastInst::Create(CastInst::getCastOpcode(ICmpScaledV, false,
OpTy, false),
ICmpScaledV, OpTy, "tmp", CI);
ICmpScaledV = Cast;
}
CI->setOperand(1, ICmpScaledV);
} else {
// A scale of 1 means that the scale has been expanded as part of the
// base regs.
assert((F.Scale == 0 || F.Scale == 1) &&
"ICmp does not support folding a global value and "
"a scale at the same time!");
Constant *C = ConstantInt::getSigned(SE.getEffectiveSCEVType(OpTy),
-(uint64_t)Offset);
if (C->getType() != OpTy)
C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
OpTy, false),
C, OpTy);
CI->setOperand(1, C);
}
}
return FullV;
}
/// Helper for Rewrite. PHI nodes are special because the use of their operands
/// effectively happens in their predecessor blocks, so the expression may need
/// to be expanded in multiple places.
void LSRInstance::RewriteForPHI(PHINode *PN,
const LSRUse &LU,
const LSRFixup &LF,
const Formula &F,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const {
DenseMap<BasicBlock *, Value *> Inserted;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == LF.OperandValToReplace) {
BasicBlock *BB = PN->getIncomingBlock(i);
// If this is a critical edge, split the edge so that we do not insert
// the code on all predecessor/successor paths. We do this unless this
// is the canonical backedge for this loop, which complicates post-inc
// users.
if (e != 1 && BB->getTerminator()->getNumSuccessors() > 1 &&
!isa<IndirectBrInst>(BB->getTerminator())) {
BasicBlock *Parent = PN->getParent();
Loop *PNLoop = LI.getLoopFor(Parent);
if (!PNLoop || Parent != PNLoop->getHeader()) {
// Split the critical edge.
BasicBlock *NewBB = nullptr;
if (!Parent->isLandingPad()) {
NewBB = SplitCriticalEdge(BB, Parent,
CriticalEdgeSplittingOptions(&DT, &LI)
.setMergeIdenticalEdges()
.setDontDeleteUselessPHIs());
} else {
SmallVector<BasicBlock*, 2> NewBBs;
SplitLandingPadPredecessors(Parent, BB, "", "", NewBBs, &DT, &LI);
NewBB = NewBBs[0];
}
// If NewBB==NULL, then SplitCriticalEdge refused to split because all
// phi predecessors are identical. The simple thing to do is skip
// splitting in this case rather than complicate the API.
if (NewBB) {
// If PN is outside of the loop and BB is in the loop, we want to
// move the block to be immediately before the PHI block, not
// immediately after BB.
if (L->contains(BB) && !L->contains(PN))
NewBB->moveBefore(PN->getParent());
// Splitting the edge can reduce the number of PHI entries we have.
e = PN->getNumIncomingValues();
BB = NewBB;
i = PN->getBasicBlockIndex(BB);
}
}
}
std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> Pair =
Inserted.insert(std::make_pair(BB, static_cast<Value *>(nullptr)));
if (!Pair.second)
PN->setIncomingValue(i, Pair.first->second);
else {
Value *FullV = Expand(LU, LF, F, BB->getTerminator()->getIterator(),
Rewriter, DeadInsts);
// If this is reuse-by-noop-cast, insert the noop cast.
Type *OpTy = LF.OperandValToReplace->getType();
if (FullV->getType() != OpTy)
FullV =
CastInst::Create(CastInst::getCastOpcode(FullV, false,
OpTy, false),
FullV, LF.OperandValToReplace->getType(),
"tmp", BB->getTerminator());
PN->setIncomingValue(i, FullV);
Pair.first->second = FullV;
}
}
}
/// Emit instructions for the leading candidate expression for this LSRUse (this
/// is called "expanding"), and update the UserInst to reference the newly
/// expanded value.
void LSRInstance::Rewrite(const LSRUse &LU,
const LSRFixup &LF,
const Formula &F,
SCEVExpander &Rewriter,
SmallVectorImpl<WeakVH> &DeadInsts) const {
// First, find an insertion point that dominates UserInst. For PHI nodes,
// find the nearest block which dominates all the relevant uses.
if (PHINode *PN = dyn_cast<PHINode>(LF.UserInst)) {
RewriteForPHI(PN, LU, LF, F, Rewriter, DeadInsts);
} else {
Value *FullV =
Expand(LU, LF, F, LF.UserInst->getIterator(), Rewriter, DeadInsts);
// If this is reuse-by-noop-cast, insert the noop cast.
Type *OpTy = LF.OperandValToReplace->getType();
if (FullV->getType() != OpTy) {
Instruction *Cast =
CastInst::Create(CastInst::getCastOpcode(FullV, false, OpTy, false),
FullV, OpTy, "tmp", LF.UserInst);
FullV = Cast;
}
// Update the user. ICmpZero is handled specially here (for now) because
// Expand may have updated one of the operands of the icmp already, and
// its new value may happen to be equal to LF.OperandValToReplace, in
// which case doing replaceUsesOfWith leads to replacing both operands
// with the same value. TODO: Reorganize this.
if (LU.Kind == LSRUse::ICmpZero)
LF.UserInst->setOperand(0, FullV);
else
LF.UserInst->replaceUsesOfWith(LF.OperandValToReplace, FullV);
}
DeadInsts.emplace_back(LF.OperandValToReplace);
}
/// Rewrite all the fixup locations with new values, following the chosen
/// solution.
void LSRInstance::ImplementSolution(
const SmallVectorImpl<const Formula *> &Solution) {
// Keep track of instructions we may have made dead, so that
// we can remove them after we are done working.
SmallVector<WeakVH, 16> DeadInsts;
SCEVExpander Rewriter(SE, L->getHeader()->getModule()->getDataLayout(),
"lsr");
#ifndef NDEBUG
Rewriter.setDebugType(DEBUG_TYPE);
#endif
Rewriter.disableCanonicalMode();
Rewriter.enableLSRMode();
Rewriter.setIVIncInsertPos(L, IVIncInsertPos);
// Mark phi nodes that terminate chains so the expander tries to reuse them.
for (const IVChain &Chain : IVChainVec) {
if (PHINode *PN = dyn_cast<PHINode>(Chain.tailUserInst()))
Rewriter.setChainedPhi(PN);
}
// Expand the new value definitions and update the users.
for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx)
for (const LSRFixup &Fixup : Uses[LUIdx].Fixups) {
Rewrite(Uses[LUIdx], Fixup, *Solution[LUIdx], Rewriter, DeadInsts);
Changed = true;
}
for (const IVChain &Chain : IVChainVec) {
GenerateIVChain(Chain, Rewriter, DeadInsts);
Changed = true;
}
// Clean up after ourselves. This must be done before deleting any
// instructions.
Rewriter.clear();
Changed |= DeleteTriviallyDeadInstructions(DeadInsts);
}
LSRInstance::LSRInstance(Loop *L, IVUsers &IU, ScalarEvolution &SE,
DominatorTree &DT, LoopInfo &LI,
const TargetTransformInfo &TTI)
: IU(IU), SE(SE), DT(DT), LI(LI), TTI(TTI), L(L), Changed(false),
IVIncInsertPos(nullptr) {
// If LoopSimplify form is not available, stay out of trouble.
if (!L->isLoopSimplifyForm())
return;
// If there's no interesting work to be done, bail early.
if (IU.empty()) return;
// If there's too much analysis to be done, bail early. We won't be able to
// model the problem anyway.
unsigned NumUsers = 0;
for (const IVStrideUse &U : IU) {
if (++NumUsers > MaxIVUsers) {
(void)U;
DEBUG(dbgs() << "LSR skipping loop, too many IV Users in " << U << "\n");
return;
}
// Bail out if we have a PHI on an EHPad that gets a value from a
// CatchSwitchInst. Because the CatchSwitchInst cannot be split, there is
// no good place to stick any instructions.
if (auto *PN = dyn_cast<PHINode>(U.getUser())) {
auto *FirstNonPHI = PN->getParent()->getFirstNonPHI();
if (isa<FuncletPadInst>(FirstNonPHI) ||
isa<CatchSwitchInst>(FirstNonPHI))
for (BasicBlock *PredBB : PN->blocks())
if (isa<CatchSwitchInst>(PredBB->getFirstNonPHI()))
return;
}
}
#ifndef NDEBUG
// All dominating loops must have preheaders, or SCEVExpander may not be able
// to materialize an AddRecExpr whose Start is an outer AddRecExpr.
//
// IVUsers analysis should only create users that are dominated by simple loop
// headers. Since this loop should dominate all of its users, its user list
// should be empty if this loop itself is not within a simple loop nest.
for (DomTreeNode *Rung = DT.getNode(L->getLoopPreheader());
Rung; Rung = Rung->getIDom()) {
BasicBlock *BB = Rung->getBlock();
const Loop *DomLoop = LI.getLoopFor(BB);
if (DomLoop && DomLoop->getHeader() == BB) {
assert(DomLoop->getLoopPreheader() && "LSR needs a simplified loop nest");
}
}
#endif // DEBUG
DEBUG(dbgs() << "\nLSR on loop ";
L->getHeader()->printAsOperand(dbgs(), /*PrintType=*/false);
dbgs() << ":\n");
// First, perform some low-level loop optimizations.
OptimizeShadowIV();
OptimizeLoopTermCond();
// If loop preparation eliminates all interesting IV users, bail.
if (IU.empty()) return;
// Skip nested loops until we can model them better with formulae.
if (!L->empty()) {
DEBUG(dbgs() << "LSR skipping outer loop " << *L << "\n");
return;
}
// Start collecting data and preparing for the solver.
CollectChains();
CollectInterestingTypesAndFactors();
CollectFixupsAndInitialFormulae();
CollectLoopInvariantFixupsAndFormulae();
assert(!Uses.empty() && "IVUsers reported at least one use");
DEBUG(dbgs() << "LSR found " << Uses.size() << " uses:\n";
print_uses(dbgs()));
// Now use the reuse data to generate a bunch of interesting ways
// to formulate the values needed for the uses.
GenerateAllReuseFormulae();
FilterOutUndesirableDedicatedRegisters();
NarrowSearchSpaceUsingHeuristics();
SmallVector<const Formula *, 8> Solution;
Solve(Solution);
// Release memory that is no longer needed.
Factors.clear();
Types.clear();
RegUses.clear();
if (Solution.empty())
return;
#ifndef NDEBUG
// Formulae should be legal.
for (const LSRUse &LU : Uses) {
for (const Formula &F : LU.Formulae)
assert(isLegalUse(TTI, LU.MinOffset, LU.MaxOffset, LU.Kind, LU.AccessTy,
F) && "Illegal formula generated!");
};
#endif
// Now that we've decided what we want, make it so.
ImplementSolution(Solution);
}
void LSRInstance::print_factors_and_types(raw_ostream &OS) const {
if (Factors.empty() && Types.empty()) return;
OS << "LSR has identified the following interesting factors and types: ";
bool First = true;
for (int64_t Factor : Factors) {
if (!First) OS << ", ";
First = false;
OS << '*' << Factor;
}
for (Type *Ty : Types) {
if (!First) OS << ", ";
First = false;
OS << '(' << *Ty << ')';
}
OS << '\n';
}
void LSRInstance::print_fixups(raw_ostream &OS) const {
OS << "LSR is examining the following fixup sites:\n";
for (const LSRUse &LU : Uses)
for (const LSRFixup &LF : LU.Fixups) {
dbgs() << " ";
LF.print(OS);
OS << '\n';
}
}
void LSRInstance::print_uses(raw_ostream &OS) const {
OS << "LSR is examining the following uses:\n";
for (const LSRUse &LU : Uses) {
dbgs() << " ";
LU.print(OS);
OS << '\n';
for (const Formula &F : LU.Formulae) {
OS << " ";
F.print(OS);
OS << '\n';
}
}
}
void LSRInstance::print(raw_ostream &OS) const {
print_factors_and_types(OS);
print_fixups(OS);
print_uses(OS);
}
LLVM_DUMP_METHOD
void LSRInstance::dump() const {
print(errs()); errs() << '\n';
}
namespace {
class LoopStrengthReduce : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopStrengthReduce();
private:
bool runOnLoop(Loop *L, LPPassManager &LPM) override;
void getAnalysisUsage(AnalysisUsage &AU) const override;
};
}
char LoopStrengthReduce::ID = 0;
INITIALIZE_PASS_BEGIN(LoopStrengthReduce, "loop-reduce",
"Loop Strength Reduction", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(IVUsersWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_END(LoopStrengthReduce, "loop-reduce",
"Loop Strength Reduction", false, false)
Pass *llvm::createLoopStrengthReducePass() { return new LoopStrengthReduce(); }
LoopStrengthReduce::LoopStrengthReduce() : LoopPass(ID) {
initializeLoopStrengthReducePass(*PassRegistry::getPassRegistry());
}
void LoopStrengthReduce::getAnalysisUsage(AnalysisUsage &AU) const {
// We split critical edges, so we change the CFG. However, we do update
// many analyses if they are around.
AU.addPreservedID(LoopSimplifyID);
AU.addRequired<LoopInfoWrapperPass>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addPreserved<ScalarEvolutionWrapperPass>();
// Requiring LoopSimplify a second time here prevents IVUsers from running
// twice, since LoopSimplify was invalidated by running ScalarEvolution.
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<IVUsersWrapperPass>();
AU.addPreserved<IVUsersWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
}
static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
DominatorTree &DT, LoopInfo &LI,
const TargetTransformInfo &TTI) {
bool Changed = false;
// Run the main LSR transformation.
Changed |= LSRInstance(L, IU, SE, DT, LI, TTI).getChanged();
// Remove any extra phis created by processing inner loops.
Changed |= DeleteDeadPHIs(L->getHeader());
if (EnablePhiElim && L->isLoopSimplifyForm()) {
SmallVector<WeakVH, 16> DeadInsts;
const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
SCEVExpander Rewriter(SE, DL, "lsr");
#ifndef NDEBUG
Rewriter.setDebugType(DEBUG_TYPE);
#endif
unsigned numFolded = Rewriter.replaceCongruentIVs(L, &DT, DeadInsts, &TTI);
if (numFolded) {
Changed = true;
DeleteTriviallyDeadInstructions(DeadInsts);
DeleteDeadPHIs(L->getHeader());
}
}
return Changed;
}
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager & /*LPM*/) {
if (skipLoop(L))
return false;
auto &IU = getAnalysis<IVUsersWrapperPass>().getIU();
auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
const auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
*L->getHeader()->getParent());
return ReduceLoopStrength(L, IU, SE, DT, LI, TTI);
}
PreservedAnalyses LoopStrengthReducePass::run(Loop &L,
LoopAnalysisManager &AM) {
const auto &FAM =
AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
Function *F = L.getHeader()->getParent();
auto &IU = AM.getResult<IVUsersAnalysis>(L);
auto *SE = FAM.getCachedResult<ScalarEvolutionAnalysis>(*F);
auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(*F);
auto *LI = FAM.getCachedResult<LoopAnalysis>(*F);
auto *TTI = FAM.getCachedResult<TargetIRAnalysis>(*F);
assert((SE && DT && LI && TTI) &&
"Analyses for Loop Strength Reduce not available");
if (!ReduceLoopStrength(&L, IU, *SE, *DT, *LI, *TTI))
return PreservedAnalyses::all();
return getLoopPassPreservedAnalyses();
}
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