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llvm-project/llvm/lib/Analysis/InlineCost.cpp

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//===- InlineCost.cpp - Cost analysis for inliner -------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements inline cost analysis.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/InlineCost.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Operator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "inline-cost"
STATISTIC(NumCallsAnalyzed, "Number of call sites analyzed");
static cl::opt<int> InlineThreshold(
"inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore,
cl::desc("Control the amount of inlining to perform (default = 225)"));
static cl::opt<int> HintThreshold(
"inlinehint-threshold", cl::Hidden, cl::init(325),
cl::desc("Threshold for inlining functions with inline hint"));
static cl::opt<int>
ColdCallSiteThreshold("inline-cold-callsite-threshold", cl::Hidden,
cl::init(45),
cl::desc("Threshold for inlining cold callsites"));
// We introduce this threshold to help performance of instrumentation based
// PGO before we actually hook up inliner with analysis passes such as BPI and
// BFI.
static cl::opt<int> ColdThreshold(
"inlinecold-threshold", cl::Hidden, cl::init(45),
cl::desc("Threshold for inlining functions with cold attribute"));
static cl::opt<int>
HotCallSiteThreshold("hot-callsite-threshold", cl::Hidden, cl::init(3000),
cl::ZeroOrMore,
cl::desc("Threshold for hot callsites "));
static cl::opt<int> LocallyHotCallSiteThreshold(
"locally-hot-callsite-threshold", cl::Hidden, cl::init(525), cl::ZeroOrMore,
cl::desc("Threshold for locally hot callsites "));
static cl::opt<int> ColdCallSiteRelFreq(
"cold-callsite-rel-freq", cl::Hidden, cl::init(2), cl::ZeroOrMore,
cl::desc("Maxmimum block frequency, expressed as a percentage of caller's "
"entry frequency, for a callsite to be cold in the absence of "
"profile information."));
static cl::opt<int> HotCallSiteRelFreq(
"hot-callsite-rel-freq", cl::Hidden, cl::init(60), cl::ZeroOrMore,
cl::desc("Minimum block frequency, expressed as a multiple of caller's "
"entry frequency, for a callsite to be hot in the absence of "
"profile information."));
static cl::opt<bool> ComputeFullInlineCost(
"inline-cost-full", cl::Hidden, cl::init(false),
cl::desc("Compute the full inline cost of a call site even when the cost "
"exceeds the threshold."));
namespace {
class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
typedef InstVisitor<CallAnalyzer, bool> Base;
friend class InstVisitor<CallAnalyzer, bool>;
/// The TargetTransformInfo available for this compilation.
const TargetTransformInfo &TTI;
/// Getter for the cache of @llvm.assume intrinsics.
std::function<AssumptionCache &(Function &)> &GetAssumptionCache;
/// Getter for BlockFrequencyInfo
Optional<function_ref<BlockFrequencyInfo &(Function &)>> &GetBFI;
/// Profile summary information.
ProfileSummaryInfo *PSI;
/// The called function.
Function &F;
// Cache the DataLayout since we use it a lot.
const DataLayout &DL;
/// The OptimizationRemarkEmitter available for this compilation.
OptimizationRemarkEmitter *ORE;
/// The candidate callsite being analyzed. Please do not use this to do
/// analysis in the caller function; we want the inline cost query to be
/// easily cacheable. Instead, use the cover function paramHasAttr.
CallSite CandidateCS;
/// Tunable parameters that control the analysis.
const InlineParams &Params;
int Threshold;
int Cost;
bool IsCallerRecursive;
bool IsRecursiveCall;
bool ExposesReturnsTwice;
bool HasDynamicAlloca;
bool ContainsNoDuplicateCall;
bool HasReturn;
bool HasIndirectBr;
bool HasFrameEscape;
/// Number of bytes allocated statically by the callee.
uint64_t AllocatedSize;
unsigned NumInstructions, NumVectorInstructions;
int VectorBonus, TenPercentVectorBonus;
// Bonus to be applied when the callee has only one reachable basic block.
int SingleBBBonus;
/// While we walk the potentially-inlined instructions, we build up and
/// maintain a mapping of simplified values specific to this callsite. The
/// idea is to propagate any special information we have about arguments to
/// this call through the inlinable section of the function, and account for
/// likely simplifications post-inlining. The most important aspect we track
/// is CFG altering simplifications -- when we prove a basic block dead, that
/// can cause dramatic shifts in the cost of inlining a function.
DenseMap<Value *, Constant *> SimplifiedValues;
/// Keep track of the values which map back (through function arguments) to
/// allocas on the caller stack which could be simplified through SROA.
DenseMap<Value *, Value *> SROAArgValues;
/// The mapping of caller Alloca values to their accumulated cost savings. If
/// we have to disable SROA for one of the allocas, this tells us how much
/// cost must be added.
DenseMap<Value *, int> SROAArgCosts;
/// Keep track of values which map to a pointer base and constant offset.
DenseMap<Value *, std::pair<Value *, APInt>> ConstantOffsetPtrs;
// Custom simplification helper routines.
bool isAllocaDerivedArg(Value *V);
bool lookupSROAArgAndCost(Value *V, Value *&Arg,
DenseMap<Value *, int>::iterator &CostIt);
void disableSROA(DenseMap<Value *, int>::iterator CostIt);
void disableSROA(Value *V);
void accumulateSROACost(DenseMap<Value *, int>::iterator CostIt,
int InstructionCost);
bool isGEPFree(GetElementPtrInst &GEP);
bool accumulateGEPOffset(GEPOperator &GEP, APInt &Offset);
bool simplifyCallSite(Function *F, CallSite CS);
template <typename Callable>
bool simplifyInstruction(Instruction &I, Callable Evaluate);
ConstantInt *stripAndComputeInBoundsConstantOffsets(Value *&V);
/// Return true if the given argument to the function being considered for
/// inlining has the given attribute set either at the call site or the
/// function declaration. Primarily used to inspect call site specific
/// attributes since these can be more precise than the ones on the callee
/// itself.
bool paramHasAttr(Argument *A, Attribute::AttrKind Attr);
/// Return true if the given value is known non null within the callee if
/// inlined through this particular callsite.
bool isKnownNonNullInCallee(Value *V);
/// Update Threshold based on callsite properties such as callee
/// attributes and callee hotness for PGO builds. The Callee is explicitly
/// passed to support analyzing indirect calls whose target is inferred by
/// analysis.
void updateThreshold(CallSite CS, Function &Callee);
/// Return true if size growth is allowed when inlining the callee at CS.
bool allowSizeGrowth(CallSite CS);
/// Return true if \p CS is a cold callsite.
bool isColdCallSite(CallSite CS, BlockFrequencyInfo *CallerBFI);
/// Return a higher threshold if \p CS is a hot callsite.
Optional<int> getHotCallSiteThreshold(CallSite CS,
BlockFrequencyInfo *CallerBFI);
// Custom analysis routines.
bool analyzeBlock(BasicBlock *BB, SmallPtrSetImpl<const Value *> &EphValues);
// Disable several entry points to the visitor so we don't accidentally use
// them by declaring but not defining them here.
void visit(Module *);
void visit(Module &);
void visit(Function *);
void visit(Function &);
void visit(BasicBlock *);
void visit(BasicBlock &);
// Provide base case for our instruction visit.
bool visitInstruction(Instruction &I);
// Our visit overrides.
bool visitAlloca(AllocaInst &I);
bool visitPHI(PHINode &I);
bool visitGetElementPtr(GetElementPtrInst &I);
bool visitBitCast(BitCastInst &I);
bool visitPtrToInt(PtrToIntInst &I);
bool visitIntToPtr(IntToPtrInst &I);
bool visitCastInst(CastInst &I);
bool visitUnaryInstruction(UnaryInstruction &I);
bool visitCmpInst(CmpInst &I);
bool visitAnd(BinaryOperator &I);
bool visitOr(BinaryOperator &I);
bool visitSub(BinaryOperator &I);
bool visitBinaryOperator(BinaryOperator &I);
bool visitLoad(LoadInst &I);
bool visitStore(StoreInst &I);
bool visitExtractValue(ExtractValueInst &I);
bool visitInsertValue(InsertValueInst &I);
bool visitCallSite(CallSite CS);
bool visitReturnInst(ReturnInst &RI);
bool visitBranchInst(BranchInst &BI);
bool visitSwitchInst(SwitchInst &SI);
bool visitIndirectBrInst(IndirectBrInst &IBI);
bool visitResumeInst(ResumeInst &RI);
bool visitCleanupReturnInst(CleanupReturnInst &RI);
bool visitCatchReturnInst(CatchReturnInst &RI);
bool visitUnreachableInst(UnreachableInst &I);
public:
CallAnalyzer(const TargetTransformInfo &TTI,
std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
Optional<function_ref<BlockFrequencyInfo &(Function &)>> &GetBFI,
ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE,
Function &Callee, CallSite CSArg, const InlineParams &Params)
: TTI(TTI), GetAssumptionCache(GetAssumptionCache), GetBFI(GetBFI),
PSI(PSI), F(Callee), DL(F.getParent()->getDataLayout()), ORE(ORE),
CandidateCS(CSArg), Params(Params), Threshold(Params.DefaultThreshold),
Cost(0), IsCallerRecursive(false), IsRecursiveCall(false),
ExposesReturnsTwice(false), HasDynamicAlloca(false),
ContainsNoDuplicateCall(false), HasReturn(false), HasIndirectBr(false),
HasFrameEscape(false), AllocatedSize(0), NumInstructions(0),
NumVectorInstructions(0), VectorBonus(0), SingleBBBonus(0),
NumConstantArgs(0), NumConstantOffsetPtrArgs(0), NumAllocaArgs(0),
NumConstantPtrCmps(0), NumConstantPtrDiffs(0),
NumInstructionsSimplified(0), SROACostSavings(0),
SROACostSavingsLost(0) {}
bool analyzeCall(CallSite CS);
int getThreshold() { return Threshold; }
int getCost() { return Cost; }
// Keep a bunch of stats about the cost savings found so we can print them
// out when debugging.
unsigned NumConstantArgs;
unsigned NumConstantOffsetPtrArgs;
unsigned NumAllocaArgs;
unsigned NumConstantPtrCmps;
unsigned NumConstantPtrDiffs;
unsigned NumInstructionsSimplified;
unsigned SROACostSavings;
unsigned SROACostSavingsLost;
void dump();
};
} // namespace
/// \brief Test whether the given value is an Alloca-derived function argument.
bool CallAnalyzer::isAllocaDerivedArg(Value *V) {
return SROAArgValues.count(V);
}
/// \brief Lookup the SROA-candidate argument and cost iterator which V maps to.
/// Returns false if V does not map to a SROA-candidate.
bool CallAnalyzer::lookupSROAArgAndCost(
Value *V, Value *&Arg, DenseMap<Value *, int>::iterator &CostIt) {
if (SROAArgValues.empty() || SROAArgCosts.empty())
return false;
DenseMap<Value *, Value *>::iterator ArgIt = SROAArgValues.find(V);
if (ArgIt == SROAArgValues.end())
return false;
Arg = ArgIt->second;
CostIt = SROAArgCosts.find(Arg);
return CostIt != SROAArgCosts.end();
}
/// \brief Disable SROA for the candidate marked by this cost iterator.
///
/// This marks the candidate as no longer viable for SROA, and adds the cost
/// savings associated with it back into the inline cost measurement.
void CallAnalyzer::disableSROA(DenseMap<Value *, int>::iterator CostIt) {
// If we're no longer able to perform SROA we need to undo its cost savings
// and prevent subsequent analysis.
Cost += CostIt->second;
SROACostSavings -= CostIt->second;
SROACostSavingsLost += CostIt->second;
SROAArgCosts.erase(CostIt);
}
/// \brief If 'V' maps to a SROA candidate, disable SROA for it.
void CallAnalyzer::disableSROA(Value *V) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(V, SROAArg, CostIt))
disableSROA(CostIt);
}
/// \brief Accumulate the given cost for a particular SROA candidate.
void CallAnalyzer::accumulateSROACost(DenseMap<Value *, int>::iterator CostIt,
int InstructionCost) {
CostIt->second += InstructionCost;
SROACostSavings += InstructionCost;
}
/// \brief Accumulate a constant GEP offset into an APInt if possible.
///
/// Returns false if unable to compute the offset for any reason. Respects any
/// simplified values known during the analysis of this callsite.
bool CallAnalyzer::accumulateGEPOffset(GEPOperator &GEP, APInt &Offset) {
unsigned IntPtrWidth = DL.getPointerSizeInBits();
assert(IntPtrWidth == Offset.getBitWidth());
for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
GTI != GTE; ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
if (!OpC)
if (Constant *SimpleOp = SimplifiedValues.lookup(GTI.getOperand()))
OpC = dyn_cast<ConstantInt>(SimpleOp);
if (!OpC)
return false;
if (OpC->isZero())
continue;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = GTI.getStructTypeOrNull()) {
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
Offset += APInt(IntPtrWidth, SL->getElementOffset(ElementIdx));
continue;
}
APInt TypeSize(IntPtrWidth, DL.getTypeAllocSize(GTI.getIndexedType()));
Offset += OpC->getValue().sextOrTrunc(IntPtrWidth) * TypeSize;
}
return true;
}
/// \brief Use TTI to check whether a GEP is free.
///
/// Respects any simplified values known during the analysis of this callsite.
bool CallAnalyzer::isGEPFree(GetElementPtrInst &GEP) {
SmallVector<Value *, 4> Operands;
Operands.push_back(GEP.getOperand(0));
for (User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); I != E; ++I)
if (Constant *SimpleOp = SimplifiedValues.lookup(*I))
Operands.push_back(SimpleOp);
else
Operands.push_back(*I);
return TargetTransformInfo::TCC_Free == TTI.getUserCost(&GEP, Operands);
}
bool CallAnalyzer::visitAlloca(AllocaInst &I) {
// Check whether inlining will turn a dynamic alloca into a static
// alloca and handle that case.
if (I.isArrayAllocation()) {
Constant *Size = SimplifiedValues.lookup(I.getArraySize());
if (auto *AllocSize = dyn_cast_or_null<ConstantInt>(Size)) {
Type *Ty = I.getAllocatedType();
AllocatedSize = SaturatingMultiplyAdd(
AllocSize->getLimitedValue(), DL.getTypeAllocSize(Ty), AllocatedSize);
return Base::visitAlloca(I);
}
}
// Accumulate the allocated size.
if (I.isStaticAlloca()) {
Type *Ty = I.getAllocatedType();
AllocatedSize = SaturatingAdd(DL.getTypeAllocSize(Ty), AllocatedSize);
}
// We will happily inline static alloca instructions.
if (I.isStaticAlloca())
return Base::visitAlloca(I);
// FIXME: This is overly conservative. Dynamic allocas are inefficient for
// a variety of reasons, and so we would like to not inline them into
// functions which don't currently have a dynamic alloca. This simply
// disables inlining altogether in the presence of a dynamic alloca.
HasDynamicAlloca = true;
return false;
}
bool CallAnalyzer::visitPHI(PHINode &I) {
// FIXME: We should potentially be tracking values through phi nodes,
// especially when they collapse to a single value due to deleted CFG edges
// during inlining.
// FIXME: We need to propagate SROA *disabling* through phi nodes, even
// though we don't want to propagate it's bonuses. The idea is to disable
// SROA if it *might* be used in an inappropriate manner.
// Phi nodes are always zero-cost.
return true;
}
bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
bool SROACandidate =
lookupSROAArgAndCost(I.getPointerOperand(), SROAArg, CostIt);
// Try to fold GEPs of constant-offset call site argument pointers. This
// requires target data and inbounds GEPs.
if (I.isInBounds()) {
// Check if we have a base + offset for the pointer.
Value *Ptr = I.getPointerOperand();
std::pair<Value *, APInt> BaseAndOffset = ConstantOffsetPtrs.lookup(Ptr);
if (BaseAndOffset.first) {
// Check if the offset of this GEP is constant, and if so accumulate it
// into Offset.
if (!accumulateGEPOffset(cast<GEPOperator>(I), BaseAndOffset.second)) {
// Non-constant GEPs aren't folded, and disable SROA.
if (SROACandidate)
disableSROA(CostIt);
return isGEPFree(I);
}
// Add the result as a new mapping to Base + Offset.
ConstantOffsetPtrs[&I] = BaseAndOffset;
// Also handle SROA candidates here, we already know that the GEP is
// all-constant indexed.
if (SROACandidate)
SROAArgValues[&I] = SROAArg;
return true;
}
}
// Lambda to check whether a GEP's indices are all constant.
auto IsGEPOffsetConstant = [&](GetElementPtrInst &GEP) {
for (User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end(); I != E; ++I)
if (!isa<Constant>(*I) && !SimplifiedValues.lookup(*I))
return false;
return true;
};
if (IsGEPOffsetConstant(I)) {
if (SROACandidate)
SROAArgValues[&I] = SROAArg;
// Constant GEPs are modeled as free.
return true;
}
// Variable GEPs will require math and will disable SROA.
if (SROACandidate)
disableSROA(CostIt);
return isGEPFree(I);
}
/// Simplify \p I if its operands are constants and update SimplifiedValues.
/// \p Evaluate is a callable specific to instruction type that evaluates the
/// instruction when all the operands are constants.
template <typename Callable>
bool CallAnalyzer::simplifyInstruction(Instruction &I, Callable Evaluate) {
SmallVector<Constant *, 2> COps;
for (Value *Op : I.operands()) {
Constant *COp = dyn_cast<Constant>(Op);
if (!COp)
COp = SimplifiedValues.lookup(Op);
if (!COp)
return false;
COps.push_back(COp);
}
auto *C = Evaluate(COps);
if (!C)
return false;
SimplifiedValues[&I] = C;
return true;
}
bool CallAnalyzer::visitBitCast(BitCastInst &I) {
// Propagate constants through bitcasts.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getBitCast(COps[0], I.getType());
}))
return true;
// Track base/offsets through casts
std::pair<Value *, APInt> BaseAndOffset =
ConstantOffsetPtrs.lookup(I.getOperand(0));
// Casts don't change the offset, just wrap it up.
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
// Also look for SROA candidates here.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
// Bitcasts are always zero cost.
return true;
}
bool CallAnalyzer::visitPtrToInt(PtrToIntInst &I) {
// Propagate constants through ptrtoint.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getPtrToInt(COps[0], I.getType());
}))
return true;
// Track base/offset pairs when converted to a plain integer provided the
// integer is large enough to represent the pointer.
unsigned IntegerSize = I.getType()->getScalarSizeInBits();
if (IntegerSize >= DL.getPointerSizeInBits()) {
std::pair<Value *, APInt> BaseAndOffset =
ConstantOffsetPtrs.lookup(I.getOperand(0));
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
}
// This is really weird. Technically, ptrtoint will disable SROA. However,
// unless that ptrtoint is *used* somewhere in the live basic blocks after
// inlining, it will be nuked, and SROA should proceed. All of the uses which
// would block SROA would also block SROA if applied directly to a pointer,
// and so we can just add the integer in here. The only places where SROA is
// preserved either cannot fire on an integer, or won't in-and-of themselves
// disable SROA (ext) w/o some later use that we would see and disable.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
return TargetTransformInfo::TCC_Free == TTI.getUserCost(&I);
}
bool CallAnalyzer::visitIntToPtr(IntToPtrInst &I) {
// Propagate constants through ptrtoint.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getIntToPtr(COps[0], I.getType());
}))
return true;
// Track base/offset pairs when round-tripped through a pointer without
// modifications provided the integer is not too large.
Value *Op = I.getOperand(0);
unsigned IntegerSize = Op->getType()->getScalarSizeInBits();
if (IntegerSize <= DL.getPointerSizeInBits()) {
std::pair<Value *, APInt> BaseAndOffset = ConstantOffsetPtrs.lookup(Op);
if (BaseAndOffset.first)
ConstantOffsetPtrs[&I] = BaseAndOffset;
}
// "Propagate" SROA here in the same manner as we do for ptrtoint above.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(Op, SROAArg, CostIt))
SROAArgValues[&I] = SROAArg;
return TargetTransformInfo::TCC_Free == TTI.getUserCost(&I);
}
bool CallAnalyzer::visitCastInst(CastInst &I) {
// Propagate constants through ptrtoint.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getCast(I.getOpcode(), COps[0], I.getType());
}))
return true;
// Disable SROA in the face of arbitrary casts we don't whitelist elsewhere.
disableSROA(I.getOperand(0));
return TargetTransformInfo::TCC_Free == TTI.getUserCost(&I);
}
bool CallAnalyzer::visitUnaryInstruction(UnaryInstruction &I) {
Value *Operand = I.getOperand(0);
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantFoldInstOperands(&I, COps[0], DL);
}))
return true;
// Disable any SROA on the argument to arbitrary unary operators.
disableSROA(Operand);
return false;
}
bool CallAnalyzer::paramHasAttr(Argument *A, Attribute::AttrKind Attr) {
return CandidateCS.paramHasAttr(A->getArgNo(), Attr);
}
bool CallAnalyzer::isKnownNonNullInCallee(Value *V) {
// Does the *call site* have the NonNull attribute set on an argument? We
// use the attribute on the call site to memoize any analysis done in the
// caller. This will also trip if the callee function has a non-null
// parameter attribute, but that's a less interesting case because hopefully
// the callee would already have been simplified based on that.
if (Argument *A = dyn_cast<Argument>(V))
if (paramHasAttr(A, Attribute::NonNull))
return true;
// Is this an alloca in the caller? This is distinct from the attribute case
// above because attributes aren't updated within the inliner itself and we
// always want to catch the alloca derived case.
if (isAllocaDerivedArg(V))
// We can actually predict the result of comparisons between an
// alloca-derived value and null. Note that this fires regardless of
// SROA firing.
return true;
return false;
}
bool CallAnalyzer::allowSizeGrowth(CallSite CS) {
// If the normal destination of the invoke or the parent block of the call
// site is unreachable-terminated, there is little point in inlining this
// unless there is literally zero cost.
// FIXME: Note that it is possible that an unreachable-terminated block has a
// hot entry. For example, in below scenario inlining hot_call_X() may be
// beneficial :
// main() {
// hot_call_1();
// ...
// hot_call_N()
// exit(0);
// }
// For now, we are not handling this corner case here as it is rare in real
// code. In future, we should elaborate this based on BPI and BFI in more
// general threshold adjusting heuristics in updateThreshold().
Instruction *Instr = CS.getInstruction();
if (InvokeInst *II = dyn_cast<InvokeInst>(Instr)) {
if (isa<UnreachableInst>(II->getNormalDest()->getTerminator()))
return false;
} else if (isa<UnreachableInst>(Instr->getParent()->getTerminator()))
return false;
return true;
}
bool CallAnalyzer::isColdCallSite(CallSite CS, BlockFrequencyInfo *CallerBFI) {
// If global profile summary is available, then callsite's coldness is
// determined based on that.
if (PSI && PSI->hasProfileSummary())
return PSI->isColdCallSite(CS, CallerBFI);
// Otherwise we need BFI to be available.
if (!CallerBFI)
return false;
// Determine if the callsite is cold relative to caller's entry. We could
// potentially cache the computation of scaled entry frequency, but the added
// complexity is not worth it unless this scaling shows up high in the
// profiles.
const BranchProbability ColdProb(ColdCallSiteRelFreq, 100);
auto CallSiteBB = CS.getInstruction()->getParent();
auto CallSiteFreq = CallerBFI->getBlockFreq(CallSiteBB);
auto CallerEntryFreq =
CallerBFI->getBlockFreq(&(CS.getCaller()->getEntryBlock()));
return CallSiteFreq < CallerEntryFreq * ColdProb;
}
Optional<int>
CallAnalyzer::getHotCallSiteThreshold(CallSite CS,
BlockFrequencyInfo *CallerBFI) {
// If global profile summary is available, then callsite's hotness is
// determined based on that.
if (PSI && PSI->hasProfileSummary() && PSI->isHotCallSite(CS, CallerBFI))
return Params.HotCallSiteThreshold;
// Otherwise we need BFI to be available and to have a locally hot callsite
// threshold.
if (!CallerBFI || !Params.LocallyHotCallSiteThreshold)
return None;
// Determine if the callsite is hot relative to caller's entry. We could
// potentially cache the computation of scaled entry frequency, but the added
// complexity is not worth it unless this scaling shows up high in the
// profiles.
auto CallSiteBB = CS.getInstruction()->getParent();
auto CallSiteFreq = CallerBFI->getBlockFreq(CallSiteBB).getFrequency();
auto CallerEntryFreq = CallerBFI->getEntryFreq();
if (CallSiteFreq >= CallerEntryFreq * HotCallSiteRelFreq)
return Params.LocallyHotCallSiteThreshold;
// Otherwise treat it normally.
return None;
}
void CallAnalyzer::updateThreshold(CallSite CS, Function &Callee) {
// If no size growth is allowed for this inlining, set Threshold to 0.
if (!allowSizeGrowth(CS)) {
Threshold = 0;
return;
}
Function *Caller = CS.getCaller();
// return min(A, B) if B is valid.
auto MinIfValid = [](int A, Optional<int> B) {
return B ? std::min(A, B.getValue()) : A;
};
// return max(A, B) if B is valid.
auto MaxIfValid = [](int A, Optional<int> B) {
return B ? std::max(A, B.getValue()) : A;
};
// Various bonus percentages. These are multiplied by Threshold to get the
// bonus values.
// SingleBBBonus: This bonus is applied if the callee has a single reachable
// basic block at the given callsite context. This is speculatively applied
// and withdrawn if more than one basic block is seen.
//
// Vector bonuses: We want to more aggressively inline vector-dense kernels
// and apply this bonus based on the percentage of vector instructions. A
// bonus is applied if the vector instructions exceed 50% and half that amount
// is applied if it exceeds 10%. Note that these bonuses are some what
// arbitrary and evolved over time by accident as much as because they are
// principled bonuses.
// FIXME: It would be nice to base the bonus values on something more
// scientific.
//
// LstCallToStaticBonus: This large bonus is applied to ensure the inlining
// of the last call to a static function as inlining such functions is
// guaranteed to reduce code size.
//
// These bonus percentages may be set to 0 based on properties of the caller
// and the callsite.
int SingleBBBonusPercent = 50;
int VectorBonusPercent = 150;
int LastCallToStaticBonus = InlineConstants::LastCallToStaticBonus;
// Lambda to set all the above bonus and bonus percentages to 0.
auto DisallowAllBonuses = [&]() {
SingleBBBonusPercent = 0;
VectorBonusPercent = 0;
LastCallToStaticBonus = 0;
};
// Use the OptMinSizeThreshold or OptSizeThreshold knob if they are available
// and reduce the threshold if the caller has the necessary attribute.
if (Caller->optForMinSize()) {
Threshold = MinIfValid(Threshold, Params.OptMinSizeThreshold);
// For minsize, we want to disable the single BB bonus and the vector
// bonuses, but not the last-call-to-static bonus. Inlining the last call to
// a static function will, at the minimum, eliminate the parameter setup and
// call/return instructions.
SingleBBBonusPercent = 0;
VectorBonusPercent = 0;
} else if (Caller->optForSize())
Threshold = MinIfValid(Threshold, Params.OptSizeThreshold);
// Adjust the threshold based on inlinehint attribute and profile based
// hotness information if the caller does not have MinSize attribute.
if (!Caller->optForMinSize()) {
if (Callee.hasFnAttribute(Attribute::InlineHint))
Threshold = MaxIfValid(Threshold, Params.HintThreshold);
// FIXME: After switching to the new passmanager, simplify the logic below
// by checking only the callsite hotness/coldness as we will reliably
// have local profile information.
//
// Callsite hotness and coldness can be determined if sample profile is
// used (which adds hotness metadata to calls) or if caller's
// BlockFrequencyInfo is available.
BlockFrequencyInfo *CallerBFI = GetBFI ? &((*GetBFI)(*Caller)) : nullptr;
auto HotCallSiteThreshold = getHotCallSiteThreshold(CS, CallerBFI);
if (!Caller->optForSize() && HotCallSiteThreshold) {
DEBUG(dbgs() << "Hot callsite.\n");
// FIXME: This should update the threshold only if it exceeds the
// current threshold, but AutoFDO + ThinLTO currently relies on this
// behavior to prevent inlining of hot callsites during ThinLTO
// compile phase.
Threshold = HotCallSiteThreshold.getValue();
} else if (isColdCallSite(CS, CallerBFI)) {
DEBUG(dbgs() << "Cold callsite.\n");
// Do not apply bonuses for a cold callsite including the
// LastCallToStatic bonus. While this bonus might result in code size
// reduction, it can cause the size of a non-cold caller to increase
// preventing it from being inlined.
DisallowAllBonuses();
Threshold = MinIfValid(Threshold, Params.ColdCallSiteThreshold);
} else if (PSI) {
// Use callee's global profile information only if we have no way of
// determining this via callsite information.
if (PSI->isFunctionEntryHot(&Callee)) {
DEBUG(dbgs() << "Hot callee.\n");
// If callsite hotness can not be determined, we may still know
// that the callee is hot and treat it as a weaker hint for threshold
// increase.
Threshold = MaxIfValid(Threshold, Params.HintThreshold);
} else if (PSI->isFunctionEntryCold(&Callee)) {
DEBUG(dbgs() << "Cold callee.\n");
// Do not apply bonuses for a cold callee including the
// LastCallToStatic bonus. While this bonus might result in code size
// reduction, it can cause the size of a non-cold caller to increase
// preventing it from being inlined.
DisallowAllBonuses();
Threshold = MinIfValid(Threshold, Params.ColdThreshold);
}
}
}
// Finally, take the target-specific inlining threshold multiplier into
// account.
Threshold *= TTI.getInliningThresholdMultiplier();
SingleBBBonus = Threshold * SingleBBBonusPercent / 100;
VectorBonus = Threshold * VectorBonusPercent / 100;
bool OnlyOneCallAndLocalLinkage =
F.hasLocalLinkage() && F.hasOneUse() && &F == CS.getCalledFunction();
// If there is only one call of the function, and it has internal linkage,
// the cost of inlining it drops dramatically. It may seem odd to update
// Cost in updateThreshold, but the bonus depends on the logic in this method.
if (OnlyOneCallAndLocalLinkage)
Cost -= LastCallToStaticBonus;
}
bool CallAnalyzer::visitCmpInst(CmpInst &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
// First try to handle simplified comparisons.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getCompare(I.getPredicate(), COps[0], COps[1]);
}))
return true;
if (I.getOpcode() == Instruction::FCmp)
return false;
// Otherwise look for a comparison between constant offset pointers with
// a common base.
Value *LHSBase, *RHSBase;
APInt LHSOffset, RHSOffset;
std::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS);
if (LHSBase) {
std::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS);
if (RHSBase && LHSBase == RHSBase) {
// We have common bases, fold the icmp to a constant based on the
// offsets.
Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset);
Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset);
if (Constant *C = ConstantExpr::getICmp(I.getPredicate(), CLHS, CRHS)) {
SimplifiedValues[&I] = C;
++NumConstantPtrCmps;
return true;
}
}
}
// If the comparison is an equality comparison with null, we can simplify it
// if we know the value (argument) can't be null
if (I.isEquality() && isa<ConstantPointerNull>(I.getOperand(1)) &&
isKnownNonNullInCallee(I.getOperand(0))) {
bool IsNotEqual = I.getPredicate() == CmpInst::ICMP_NE;
SimplifiedValues[&I] = IsNotEqual ? ConstantInt::getTrue(I.getType())
: ConstantInt::getFalse(I.getType());
return true;
}
// Finally check for SROA candidates in comparisons.
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getOperand(0), SROAArg, CostIt)) {
if (isa<ConstantPointerNull>(I.getOperand(1))) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitOr(BinaryOperator &I) {
// This is necessary because the generic simplify instruction only works if
// both operands are constants.
for (unsigned i = 0; i < 2; ++i) {
if (ConstantInt *C = dyn_cast_or_null<ConstantInt>(
SimplifiedValues.lookup(I.getOperand(i))))
if (C->isAllOnesValue()) {
SimplifiedValues[&I] = C;
return true;
}
}
return Base::visitOr(I);
}
bool CallAnalyzer::visitAnd(BinaryOperator &I) {
// This is necessary because the generic simplify instruction only works if
// both operands are constants.
for (unsigned i = 0; i < 2; ++i) {
if (ConstantInt *C = dyn_cast_or_null<ConstantInt>(
SimplifiedValues.lookup(I.getOperand(i))))
if (C->isZero()) {
SimplifiedValues[&I] = C;
return true;
}
}
return Base::visitAnd(I);
}
bool CallAnalyzer::visitSub(BinaryOperator &I) {
// Try to handle a special case: we can fold computing the difference of two
// constant-related pointers.
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
Value *LHSBase, *RHSBase;
APInt LHSOffset, RHSOffset;
std::tie(LHSBase, LHSOffset) = ConstantOffsetPtrs.lookup(LHS);
if (LHSBase) {
std::tie(RHSBase, RHSOffset) = ConstantOffsetPtrs.lookup(RHS);
if (RHSBase && LHSBase == RHSBase) {
// We have common bases, fold the subtract to a constant based on the
// offsets.
Constant *CLHS = ConstantInt::get(LHS->getContext(), LHSOffset);
Constant *CRHS = ConstantInt::get(RHS->getContext(), RHSOffset);
if (Constant *C = ConstantExpr::getSub(CLHS, CRHS)) {
SimplifiedValues[&I] = C;
++NumConstantPtrDiffs;
return true;
}
}
}
// Otherwise, fall back to the generic logic for simplifying and handling
// instructions.
return Base::visitSub(I);
}
bool CallAnalyzer::visitBinaryOperator(BinaryOperator &I) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
auto Evaluate = [&](SmallVectorImpl<Constant *> &COps) {
Value *SimpleV = nullptr;
if (auto FI = dyn_cast<FPMathOperator>(&I))
SimpleV = SimplifyFPBinOp(I.getOpcode(), COps[0], COps[1],
FI->getFastMathFlags(), DL);
else
SimpleV = SimplifyBinOp(I.getOpcode(), COps[0], COps[1], DL);
return dyn_cast_or_null<Constant>(SimpleV);
};
if (simplifyInstruction(I, Evaluate))
return true;
// Disable any SROA on arguments to arbitrary, unsimplified binary operators.
disableSROA(LHS);
disableSROA(RHS);
return false;
}
bool CallAnalyzer::visitLoad(LoadInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getPointerOperand(), SROAArg, CostIt)) {
if (I.isSimple()) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitStore(StoreInst &I) {
Value *SROAArg;
DenseMap<Value *, int>::iterator CostIt;
if (lookupSROAArgAndCost(I.getPointerOperand(), SROAArg, CostIt)) {
if (I.isSimple()) {
accumulateSROACost(CostIt, InlineConstants::InstrCost);
return true;
}
disableSROA(CostIt);
}
return false;
}
bool CallAnalyzer::visitExtractValue(ExtractValueInst &I) {
// Constant folding for extract value is trivial.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getExtractValue(COps[0], I.getIndices());
}))
return true;
// SROA can look through these but give them a cost.
return false;
}
bool CallAnalyzer::visitInsertValue(InsertValueInst &I) {
// Constant folding for insert value is trivial.
if (simplifyInstruction(I, [&](SmallVectorImpl<Constant *> &COps) {
return ConstantExpr::getInsertValue(/*AggregateOperand*/ COps[0],
/*InsertedValueOperand*/ COps[1],
I.getIndices());
}))
return true;
// SROA can look through these but give them a cost.
return false;
}
/// \brief Try to simplify a call site.
///
/// Takes a concrete function and callsite and tries to actually simplify it by
/// analyzing the arguments and call itself with instsimplify. Returns true if
/// it has simplified the callsite to some other entity (a constant), making it
/// free.
bool CallAnalyzer::simplifyCallSite(Function *F, CallSite CS) {
// FIXME: Using the instsimplify logic directly for this is inefficient
// because we have to continually rebuild the argument list even when no
// simplifications can be performed. Until that is fixed with remapping
// inside of instsimplify, directly constant fold calls here.
if (!canConstantFoldCallTo(CS, F))
return false;
// Try to re-map the arguments to constants.
SmallVector<Constant *, 4> ConstantArgs;
ConstantArgs.reserve(CS.arg_size());
for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); I != E;
++I) {
Constant *C = dyn_cast<Constant>(*I);
if (!C)
C = dyn_cast_or_null<Constant>(SimplifiedValues.lookup(*I));
if (!C)
return false; // This argument doesn't map to a constant.
ConstantArgs.push_back(C);
}
if (Constant *C = ConstantFoldCall(CS, F, ConstantArgs)) {
SimplifiedValues[CS.getInstruction()] = C;
return true;
}
return false;
}
bool CallAnalyzer::visitCallSite(CallSite CS) {
if (CS.hasFnAttr(Attribute::ReturnsTwice) &&
!F.hasFnAttribute(Attribute::ReturnsTwice)) {
// This aborts the entire analysis.
ExposesReturnsTwice = true;
return false;
}
if (CS.isCall() && cast<CallInst>(CS.getInstruction())->cannotDuplicate())
ContainsNoDuplicateCall = true;
if (Function *F = CS.getCalledFunction()) {
// When we have a concrete function, first try to simplify it directly.
if (simplifyCallSite(F, CS))
return true;
// Next check if it is an intrinsic we know about.
// FIXME: Lift this into part of the InstVisitor.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
switch (II->getIntrinsicID()) {
default:
return Base::visitCallSite(CS);
case Intrinsic::load_relative:
// This is normally lowered to 4 LLVM instructions.
Cost += 3 * InlineConstants::InstrCost;
return false;
case Intrinsic::memset:
case Intrinsic::memcpy:
case Intrinsic::memmove:
// SROA can usually chew through these intrinsics, but they aren't free.
return false;
case Intrinsic::localescape:
HasFrameEscape = true;
return false;
}
}
if (F == CS.getInstruction()->getParent()->getParent()) {
// This flag will fully abort the analysis, so don't bother with anything
// else.
IsRecursiveCall = true;
return false;
}
if (TTI.isLoweredToCall(F)) {
// We account for the average 1 instruction per call argument setup
// here.
Cost += CS.arg_size() * InlineConstants::InstrCost;
// Everything other than inline ASM will also have a significant cost
// merely from making the call.
if (!isa<InlineAsm>(CS.getCalledValue()))
Cost += InlineConstants::CallPenalty;
}
return Base::visitCallSite(CS);
}
// Otherwise we're in a very special case -- an indirect function call. See
// if we can be particularly clever about this.
Value *Callee = CS.getCalledValue();
// First, pay the price of the argument setup. We account for the average
// 1 instruction per call argument setup here.
Cost += CS.arg_size() * InlineConstants::InstrCost;
// Next, check if this happens to be an indirect function call to a known
// function in this inline context. If not, we've done all we can.
Function *F = dyn_cast_or_null<Function>(SimplifiedValues.lookup(Callee));
if (!F)
return Base::visitCallSite(CS);
// If we have a constant that we are calling as a function, we can peer
// through it and see the function target. This happens not infrequently
// during devirtualization and so we want to give it a hefty bonus for
// inlining, but cap that bonus in the event that inlining wouldn't pan
// out. Pretend to inline the function, with a custom threshold.
auto IndirectCallParams = Params;
IndirectCallParams.DefaultThreshold = InlineConstants::IndirectCallThreshold;
CallAnalyzer CA(TTI, GetAssumptionCache, GetBFI, PSI, ORE, *F, CS,
IndirectCallParams);
if (CA.analyzeCall(CS)) {
// We were able to inline the indirect call! Subtract the cost from the
// threshold to get the bonus we want to apply, but don't go below zero.
Cost -= std::max(0, CA.getThreshold() - CA.getCost());
}
return Base::visitCallSite(CS);
}
bool CallAnalyzer::visitReturnInst(ReturnInst &RI) {
// At least one return instruction will be free after inlining.
bool Free = !HasReturn;
HasReturn = true;
return Free;
}
bool CallAnalyzer::visitBranchInst(BranchInst &BI) {
// We model unconditional branches as essentially free -- they really
// shouldn't exist at all, but handling them makes the behavior of the
// inliner more regular and predictable. Interestingly, conditional branches
// which will fold away are also free.
return BI.isUnconditional() || isa<ConstantInt>(BI.getCondition()) ||
dyn_cast_or_null<ConstantInt>(
SimplifiedValues.lookup(BI.getCondition()));
}
bool CallAnalyzer::visitSwitchInst(SwitchInst &SI) {
// We model unconditional switches as free, see the comments on handling
// branches.
if (isa<ConstantInt>(SI.getCondition()))
return true;
if (Value *V = SimplifiedValues.lookup(SI.getCondition()))
if (isa<ConstantInt>(V))
return true;
// Assume the most general case where the switch is lowered into
// either a jump table, bit test, or a balanced binary tree consisting of
// case clusters without merging adjacent clusters with the same
// destination. We do not consider the switches that are lowered with a mix
// of jump table/bit test/binary search tree. The cost of the switch is
// proportional to the size of the tree or the size of jump table range.
//
// NB: We convert large switches which are just used to initialize large phi
// nodes to lookup tables instead in simplify-cfg, so this shouldn't prevent
// inlining those. It will prevent inlining in cases where the optimization
// does not (yet) fire.
// Maximum valid cost increased in this function.
int CostUpperBound = INT_MAX - InlineConstants::InstrCost - 1;
// Exit early for a large switch, assuming one case needs at least one
// instruction.
// FIXME: This is not true for a bit test, but ignore such case for now to
// save compile-time.
int64_t CostLowerBound =
std::min((int64_t)CostUpperBound,
(int64_t)SI.getNumCases() * InlineConstants::InstrCost + Cost);
if (CostLowerBound > Threshold && !ComputeFullInlineCost) {
Cost = CostLowerBound;
return false;
}
unsigned JumpTableSize = 0;
unsigned NumCaseCluster =
TTI.getEstimatedNumberOfCaseClusters(SI, JumpTableSize);
// If suitable for a jump table, consider the cost for the table size and
// branch to destination.
if (JumpTableSize) {
int64_t JTCost = (int64_t)JumpTableSize * InlineConstants::InstrCost +
4 * InlineConstants::InstrCost;
Cost = std::min((int64_t)CostUpperBound, JTCost + Cost);
return false;
}
// Considering forming a binary search, we should find the number of nodes
// which is same as the number of comparisons when lowered. For a given
// number of clusters, n, we can define a recursive function, f(n), to find
// the number of nodes in the tree. The recursion is :
// f(n) = 1 + f(n/2) + f (n - n/2), when n > 3,
// and f(n) = n, when n <= 3.
// This will lead a binary tree where the leaf should be either f(2) or f(3)
// when n > 3. So, the number of comparisons from leaves should be n, while
// the number of non-leaf should be :
// 2^(log2(n) - 1) - 1
// = 2^log2(n) * 2^-1 - 1
// = n / 2 - 1.
// Considering comparisons from leaf and non-leaf nodes, we can estimate the
// number of comparisons in a simple closed form :
// n + n / 2 - 1 = n * 3 / 2 - 1
if (NumCaseCluster <= 3) {
// Suppose a comparison includes one compare and one conditional branch.
Cost += NumCaseCluster * 2 * InlineConstants::InstrCost;
return false;
}
int64_t ExpectedNumberOfCompare = 3 * (int64_t)NumCaseCluster / 2 - 1;
int64_t SwitchCost =
ExpectedNumberOfCompare * 2 * InlineConstants::InstrCost;
Cost = std::min((int64_t)CostUpperBound, SwitchCost + Cost);
return false;
}
bool CallAnalyzer::visitIndirectBrInst(IndirectBrInst &IBI) {
// We never want to inline functions that contain an indirectbr. This is
// incorrect because all the blockaddress's (in static global initializers
// for example) would be referring to the original function, and this
// indirect jump would jump from the inlined copy of the function into the
// original function which is extremely undefined behavior.
// FIXME: This logic isn't really right; we can safely inline functions with
// indirectbr's as long as no other function or global references the
// blockaddress of a block within the current function.
HasIndirectBr = true;
return false;
}
bool CallAnalyzer::visitResumeInst(ResumeInst &RI) {
// FIXME: It's not clear that a single instruction is an accurate model for
// the inline cost of a resume instruction.
return false;
}
bool CallAnalyzer::visitCleanupReturnInst(CleanupReturnInst &CRI) {
// FIXME: It's not clear that a single instruction is an accurate model for
// the inline cost of a cleanupret instruction.
return false;
}
bool CallAnalyzer::visitCatchReturnInst(CatchReturnInst &CRI) {
// FIXME: It's not clear that a single instruction is an accurate model for
// the inline cost of a catchret instruction.
return false;
}
bool CallAnalyzer::visitUnreachableInst(UnreachableInst &I) {
// FIXME: It might be reasonably to discount the cost of instructions leading
// to unreachable as they have the lowest possible impact on both runtime and
// code size.
return true; // No actual code is needed for unreachable.
}
bool CallAnalyzer::visitInstruction(Instruction &I) {
// Some instructions are free. All of the free intrinsics can also be
// handled by SROA, etc.
if (TargetTransformInfo::TCC_Free == TTI.getUserCost(&I))
return true;
// We found something we don't understand or can't handle. Mark any SROA-able
// values in the operand list as no longer viable.
for (User::op_iterator OI = I.op_begin(), OE = I.op_end(); OI != OE; ++OI)
disableSROA(*OI);
return false;
}
/// \brief Analyze a basic block for its contribution to the inline cost.
///
/// This method walks the analyzer over every instruction in the given basic
/// block and accounts for their cost during inlining at this callsite. It
/// aborts early if the threshold has been exceeded or an impossible to inline
/// construct has been detected. It returns false if inlining is no longer
/// viable, and true if inlining remains viable.
bool CallAnalyzer::analyzeBlock(BasicBlock *BB,
SmallPtrSetImpl<const Value *> &EphValues) {
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
// FIXME: Currently, the number of instructions in a function regardless of
// our ability to simplify them during inline to constants or dead code,
// are actually used by the vector bonus heuristic. As long as that's true,
// we have to special case debug intrinsics here to prevent differences in
// inlining due to debug symbols. Eventually, the number of unsimplified
// instructions shouldn't factor into the cost computation, but until then,
// hack around it here.
if (isa<DbgInfoIntrinsic>(I))
continue;
// Skip ephemeral values.
if (EphValues.count(&*I))
continue;
++NumInstructions;
if (isa<ExtractElementInst>(I) || I->getType()->isVectorTy())
++NumVectorInstructions;
// If the instruction is floating point, and the target says this operation
// is expensive or the function has the "use-soft-float" attribute, this may
// eventually become a library call. Treat the cost as such.
if (I->getType()->isFloatingPointTy()) {
// If the function has the "use-soft-float" attribute, mark it as
// expensive.
if (TTI.getFPOpCost(I->getType()) == TargetTransformInfo::TCC_Expensive ||
(F.getFnAttribute("use-soft-float").getValueAsString() == "true"))
Cost += InlineConstants::CallPenalty;
}
// If the instruction simplified to a constant, there is no cost to this
// instruction. Visit the instructions using our InstVisitor to account for
// all of the per-instruction logic. The visit tree returns true if we
// consumed the instruction in any way, and false if the instruction's base
// cost should count against inlining.
if (Base::visit(&*I))
++NumInstructionsSimplified;
else
Cost += InlineConstants::InstrCost;
using namespace ore;
// If the visit this instruction detected an uninlinable pattern, abort.
if (IsRecursiveCall || ExposesReturnsTwice || HasDynamicAlloca ||
HasIndirectBr || HasFrameEscape) {
if (ORE)
ORE->emit(OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline",
CandidateCS.getInstruction())
<< NV("Callee", &F)
<< " has uninlinable pattern and cost is not fully computed");
return false;
}
// If the caller is a recursive function then we don't want to inline
// functions which allocate a lot of stack space because it would increase
// the caller stack usage dramatically.
if (IsCallerRecursive &&
AllocatedSize > InlineConstants::TotalAllocaSizeRecursiveCaller) {
if (ORE)
ORE->emit(
OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline",
CandidateCS.getInstruction())
<< NV("Callee", &F)
<< " is recursive and allocates too much stack space. Cost is "
"not fully computed");
return false;
}
// Check if we've past the maximum possible threshold so we don't spin in
// huge basic blocks that will never inline.
if (Cost >= Threshold && !ComputeFullInlineCost)
return false;
}
return true;
}
/// \brief Compute the base pointer and cumulative constant offsets for V.
///
/// This strips all constant offsets off of V, leaving it the base pointer, and
/// accumulates the total constant offset applied in the returned constant. It
/// returns 0 if V is not a pointer, and returns the constant '0' if there are
/// no constant offsets applied.
ConstantInt *CallAnalyzer::stripAndComputeInBoundsConstantOffsets(Value *&V) {
if (!V->getType()->isPointerTy())
return nullptr;
unsigned IntPtrWidth = DL.getPointerSizeInBits();
APInt Offset = APInt::getNullValue(IntPtrWidth);
// Even though we don't look through PHI nodes, we could be called on an
// instruction in an unreachable block, which may be on a cycle.
SmallPtrSet<Value *, 4> Visited;
Visited.insert(V);
do {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
if (!GEP->isInBounds() || !accumulateGEPOffset(*GEP, Offset))
return nullptr;
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast) {
V = cast<Operator>(V)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->isInterposable())
break;
V = GA->getAliasee();
} else {
break;
}
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
} while (Visited.insert(V).second);
Type *IntPtrTy = DL.getIntPtrType(V->getContext());
return cast<ConstantInt>(ConstantInt::get(IntPtrTy, Offset));
}
/// \brief Analyze a call site for potential inlining.
///
/// Returns true if inlining this call is viable, and false if it is not
/// viable. It computes the cost and adjusts the threshold based on numerous
/// factors and heuristics. If this method returns false but the computed cost
/// is below the computed threshold, then inlining was forcibly disabled by
/// some artifact of the routine.
bool CallAnalyzer::analyzeCall(CallSite CS) {
++NumCallsAnalyzed;
// Perform some tweaks to the cost and threshold based on the direct
// callsite information.
// We want to more aggressively inline vector-dense kernels, so up the
// threshold, and we'll lower it if the % of vector instructions gets too
// low. Note that these bonuses are some what arbitrary and evolved over time
// by accident as much as because they are principled bonuses.
//
// FIXME: It would be nice to remove all such bonuses. At least it would be
// nice to base the bonus values on something more scientific.
assert(NumInstructions == 0);
assert(NumVectorInstructions == 0);
// Update the threshold based on callsite properties
updateThreshold(CS, F);
// Speculatively apply all possible bonuses to Threshold. If cost exceeds
// this Threshold any time, and cost cannot decrease, we can stop processing
// the rest of the function body.
Threshold += (SingleBBBonus + VectorBonus);
// Give out bonuses for the callsite, as the instructions setting them up
// will be gone after inlining.
Cost -= getCallsiteCost(CS, DL);
// If this function uses the coldcc calling convention, prefer not to inline
// it.
if (F.getCallingConv() == CallingConv::Cold)
Cost += InlineConstants::ColdccPenalty;
// Check if we're done. This can happen due to bonuses and penalties.
if (Cost >= Threshold && !ComputeFullInlineCost)
return false;
if (F.empty())
return true;
Function *Caller = CS.getInstruction()->getParent()->getParent();
// Check if the caller function is recursive itself.
for (User *U : Caller->users()) {
CallSite Site(U);
if (!Site)
continue;
Instruction *I = Site.getInstruction();
if (I->getParent()->getParent() == Caller) {
IsCallerRecursive = true;
break;
}
}
// Populate our simplified values by mapping from function arguments to call
// arguments with known important simplifications.
CallSite::arg_iterator CAI = CS.arg_begin();
for (Function::arg_iterator FAI = F.arg_begin(), FAE = F.arg_end();
FAI != FAE; ++FAI, ++CAI) {
assert(CAI != CS.arg_end());
if (Constant *C = dyn_cast<Constant>(CAI))
SimplifiedValues[&*FAI] = C;
Value *PtrArg = *CAI;
if (ConstantInt *C = stripAndComputeInBoundsConstantOffsets(PtrArg)) {
ConstantOffsetPtrs[&*FAI] = std::make_pair(PtrArg, C->getValue());
// We can SROA any pointer arguments derived from alloca instructions.
if (isa<AllocaInst>(PtrArg)) {
SROAArgValues[&*FAI] = PtrArg;
SROAArgCosts[PtrArg] = 0;
}
}
}
NumConstantArgs = SimplifiedValues.size();
NumConstantOffsetPtrArgs = ConstantOffsetPtrs.size();
NumAllocaArgs = SROAArgValues.size();
// FIXME: If a caller has multiple calls to a callee, we end up recomputing
// the ephemeral values multiple times (and they're completely determined by
// the callee, so this is purely duplicate work).
SmallPtrSet<const Value *, 32> EphValues;
CodeMetrics::collectEphemeralValues(&F, &GetAssumptionCache(F), EphValues);
// The worklist of live basic blocks in the callee *after* inlining. We avoid
// adding basic blocks of the callee which can be proven to be dead for this
// particular call site in order to get more accurate cost estimates. This
// requires a somewhat heavyweight iteration pattern: we need to walk the
// basic blocks in a breadth-first order as we insert live successors. To
// accomplish this, prioritizing for small iterations because we exit after
// crossing our threshold, we use a small-size optimized SetVector.
typedef SetVector<BasicBlock *, SmallVector<BasicBlock *, 16>,
SmallPtrSet<BasicBlock *, 16>>
BBSetVector;
BBSetVector BBWorklist;
BBWorklist.insert(&F.getEntryBlock());
bool SingleBB = true;
// Note that we *must not* cache the size, this loop grows the worklist.
for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
// Bail out the moment we cross the threshold. This means we'll under-count
// the cost, but only when undercounting doesn't matter.
if (Cost >= Threshold && !ComputeFullInlineCost)
break;
BasicBlock *BB = BBWorklist[Idx];
if (BB->empty())
continue;
// Disallow inlining a blockaddress. A blockaddress only has defined
// behavior for an indirect branch in the same function, and we do not
// currently support inlining indirect branches. But, the inliner may not
// see an indirect branch that ends up being dead code at a particular call
// site. If the blockaddress escapes the function, e.g., via a global
// variable, inlining may lead to an invalid cross-function reference.
if (BB->hasAddressTaken())
return false;
// Analyze the cost of this block. If we blow through the threshold, this
// returns false, and we can bail on out.
if (!analyzeBlock(BB, EphValues))
return false;
TerminatorInst *TI = BB->getTerminator();
// Add in the live successors by first checking whether we have terminator
// that may be simplified based on the values simplified by this call.
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isConditional()) {
Value *Cond = BI->getCondition();
if (ConstantInt *SimpleCond =
dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
BBWorklist.insert(BI->getSuccessor(SimpleCond->isZero() ? 1 : 0));
continue;
}
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
Value *Cond = SI->getCondition();
if (ConstantInt *SimpleCond =
dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
BBWorklist.insert(SI->findCaseValue(SimpleCond)->getCaseSuccessor());
continue;
}
}
// If we're unable to select a particular successor, just count all of
// them.
for (unsigned TIdx = 0, TSize = TI->getNumSuccessors(); TIdx != TSize;
++TIdx)
BBWorklist.insert(TI->getSuccessor(TIdx));
// If we had any successors at this point, than post-inlining is likely to
// have them as well. Note that we assume any basic blocks which existed
// due to branches or switches which folded above will also fold after
// inlining.
if (SingleBB && TI->getNumSuccessors() > 1) {
// Take off the bonus we applied to the threshold.
Threshold -= SingleBBBonus;
SingleBB = false;
}
}
bool OnlyOneCallAndLocalLinkage =
F.hasLocalLinkage() && F.hasOneUse() && &F == CS.getCalledFunction();
// If this is a noduplicate call, we can still inline as long as
// inlining this would cause the removal of the caller (so the instruction
// is not actually duplicated, just moved).
if (!OnlyOneCallAndLocalLinkage && ContainsNoDuplicateCall)
return false;
// We applied the maximum possible vector bonus at the beginning. Now,
// subtract the excess bonus, if any, from the Threshold before
// comparing against Cost.
if (NumVectorInstructions <= NumInstructions / 10)
Threshold -= VectorBonus;
else if (NumVectorInstructions <= NumInstructions / 2)
Threshold -= VectorBonus/2;
return Cost < std::max(1, Threshold);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// \brief Dump stats about this call's analysis.
LLVM_DUMP_METHOD void CallAnalyzer::dump() {
#define DEBUG_PRINT_STAT(x) dbgs() << " " #x ": " << x << "\n"
DEBUG_PRINT_STAT(NumConstantArgs);
DEBUG_PRINT_STAT(NumConstantOffsetPtrArgs);
DEBUG_PRINT_STAT(NumAllocaArgs);
DEBUG_PRINT_STAT(NumConstantPtrCmps);
DEBUG_PRINT_STAT(NumConstantPtrDiffs);
DEBUG_PRINT_STAT(NumInstructionsSimplified);
DEBUG_PRINT_STAT(NumInstructions);
DEBUG_PRINT_STAT(SROACostSavings);
DEBUG_PRINT_STAT(SROACostSavingsLost);
DEBUG_PRINT_STAT(ContainsNoDuplicateCall);
DEBUG_PRINT_STAT(Cost);
DEBUG_PRINT_STAT(Threshold);
#undef DEBUG_PRINT_STAT
}
#endif
/// \brief Test that there are no attribute conflicts between Caller and Callee
/// that prevent inlining.
static bool functionsHaveCompatibleAttributes(Function *Caller,
Function *Callee,
TargetTransformInfo &TTI) {
return TTI.areInlineCompatible(Caller, Callee) &&
AttributeFuncs::areInlineCompatible(*Caller, *Callee);
}
int llvm::getCallsiteCost(CallSite CS, const DataLayout &DL) {
int Cost = 0;
for (unsigned I = 0, E = CS.arg_size(); I != E; ++I) {
if (CS.isByValArgument(I)) {
// We approximate the number of loads and stores needed by dividing the
// size of the byval type by the target's pointer size.
PointerType *PTy = cast<PointerType>(CS.getArgument(I)->getType());
unsigned TypeSize = DL.getTypeSizeInBits(PTy->getElementType());
unsigned PointerSize = DL.getPointerSizeInBits();
// Ceiling division.
unsigned NumStores = (TypeSize + PointerSize - 1) / PointerSize;
// If it generates more than 8 stores it is likely to be expanded as an
// inline memcpy so we take that as an upper bound. Otherwise we assume
// one load and one store per word copied.
// FIXME: The maxStoresPerMemcpy setting from the target should be used
// here instead of a magic number of 8, but it's not available via
// DataLayout.
NumStores = std::min(NumStores, 8U);
Cost += 2 * NumStores * InlineConstants::InstrCost;
} else {
// For non-byval arguments subtract off one instruction per call
// argument.
Cost += InlineConstants::InstrCost;
}
}
// The call instruction also disappears after inlining.
Cost += InlineConstants::InstrCost + InlineConstants::CallPenalty;
return Cost;
}
InlineCost llvm::getInlineCost(
CallSite CS, const InlineParams &Params, TargetTransformInfo &CalleeTTI,
std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE) {
return getInlineCost(CS, CS.getCalledFunction(), Params, CalleeTTI,
GetAssumptionCache, GetBFI, PSI, ORE);
}
InlineCost llvm::getInlineCost(
CallSite CS, Function *Callee, const InlineParams &Params,
TargetTransformInfo &CalleeTTI,
std::function<AssumptionCache &(Function &)> &GetAssumptionCache,
Optional<function_ref<BlockFrequencyInfo &(Function &)>> GetBFI,
ProfileSummaryInfo *PSI, OptimizationRemarkEmitter *ORE) {
// Cannot inline indirect calls.
if (!Callee)
return llvm::InlineCost::getNever();
// Calls to functions with always-inline attributes should be inlined
// whenever possible.
if (CS.hasFnAttr(Attribute::AlwaysInline)) {
if (isInlineViable(*Callee))
return llvm::InlineCost::getAlways();
return llvm::InlineCost::getNever();
}
// Never inline functions with conflicting attributes (unless callee has
// always-inline attribute).
Function *Caller = CS.getCaller();
if (!functionsHaveCompatibleAttributes(Caller, Callee, CalleeTTI))
return llvm::InlineCost::getNever();
// Don't inline this call if the caller has the optnone attribute.
if (Caller->hasFnAttribute(Attribute::OptimizeNone))
return llvm::InlineCost::getNever();
// Don't inline functions which can be interposed at link-time. Don't inline
// functions marked noinline or call sites marked noinline.
// Note: inlining non-exact non-interposable functions is fine, since we know
// we have *a* correct implementation of the source level function.
if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
CS.isNoInline())
return llvm::InlineCost::getNever();
if (ORE)
ComputeFullInlineCost = true;
DEBUG(llvm::dbgs() << " Analyzing call of " << Callee->getName()
<< "... (caller:" << Caller->getName() << ")\n");
CallAnalyzer CA(CalleeTTI, GetAssumptionCache, GetBFI, PSI, ORE, *Callee, CS,
Params);
bool ShouldInline = CA.analyzeCall(CS);
DEBUG(CA.dump());
// Check if there was a reason to force inlining or no inlining.
if (!ShouldInline && CA.getCost() < CA.getThreshold())
return InlineCost::getNever();
if (ShouldInline && CA.getCost() >= CA.getThreshold())
return InlineCost::getAlways();
return llvm::InlineCost::get(CA.getCost(), CA.getThreshold());
}
bool llvm::isInlineViable(Function &F) {
bool ReturnsTwice = F.hasFnAttribute(Attribute::ReturnsTwice);
for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
// Disallow inlining of functions which contain indirect branches or
// blockaddresses.
if (isa<IndirectBrInst>(BI->getTerminator()) || BI->hasAddressTaken())
return false;
for (auto &II : *BI) {
CallSite CS(&II);
if (!CS)
continue;
// Disallow recursive calls.
if (&F == CS.getCalledFunction())
return false;
// Disallow calls which expose returns-twice to a function not previously
// attributed as such.
if (!ReturnsTwice && CS.isCall() &&
cast<CallInst>(CS.getInstruction())->canReturnTwice())
return false;
// Disallow inlining functions that call @llvm.localescape. Doing this
// correctly would require major changes to the inliner.
if (CS.getCalledFunction() &&
CS.getCalledFunction()->getIntrinsicID() ==
llvm::Intrinsic::localescape)
return false;
}
}
return true;
}
// APIs to create InlineParams based on command line flags and/or other
// parameters.
InlineParams llvm::getInlineParams(int Threshold) {
InlineParams Params;
// This field is the threshold to use for a callee by default. This is
// derived from one or more of:
// * optimization or size-optimization levels,
// * a value passed to createFunctionInliningPass function, or
// * the -inline-threshold flag.
// If the -inline-threshold flag is explicitly specified, that is used
// irrespective of anything else.
if (InlineThreshold.getNumOccurrences() > 0)
Params.DefaultThreshold = InlineThreshold;
else
Params.DefaultThreshold = Threshold;
// Set the HintThreshold knob from the -inlinehint-threshold.
Params.HintThreshold = HintThreshold;
// Set the HotCallSiteThreshold knob from the -hot-callsite-threshold.
Params.HotCallSiteThreshold = HotCallSiteThreshold;
// If the -locally-hot-callsite-threshold is explicitly specified, use it to
// populate LocallyHotCallSiteThreshold. Later, we populate
// Params.LocallyHotCallSiteThreshold from -locally-hot-callsite-threshold if
// we know that optimization level is O3 (in the getInlineParams variant that
// takes the opt and size levels).
// FIXME: Remove this check (and make the assignment unconditional) after
// addressing size regression issues at O2.
if (LocallyHotCallSiteThreshold.getNumOccurrences() > 0)
Params.LocallyHotCallSiteThreshold = LocallyHotCallSiteThreshold;
// Set the ColdCallSiteThreshold knob from the -inline-cold-callsite-threshold.
Params.ColdCallSiteThreshold = ColdCallSiteThreshold;
// Set the OptMinSizeThreshold and OptSizeThreshold params only if the
// -inlinehint-threshold commandline option is not explicitly given. If that
// option is present, then its value applies even for callees with size and
// minsize attributes.
// If the -inline-threshold is not specified, set the ColdThreshold from the
// -inlinecold-threshold even if it is not explicitly passed. If
// -inline-threshold is specified, then -inlinecold-threshold needs to be
// explicitly specified to set the ColdThreshold knob
if (InlineThreshold.getNumOccurrences() == 0) {
Params.OptMinSizeThreshold = InlineConstants::OptMinSizeThreshold;
Params.OptSizeThreshold = InlineConstants::OptSizeThreshold;
Params.ColdThreshold = ColdThreshold;
} else if (ColdThreshold.getNumOccurrences() > 0) {
Params.ColdThreshold = ColdThreshold;
}
return Params;
}
InlineParams llvm::getInlineParams() {
return getInlineParams(InlineThreshold);
}
// Compute the default threshold for inlining based on the opt level and the
// size opt level.
static int computeThresholdFromOptLevels(unsigned OptLevel,
unsigned SizeOptLevel) {
if (OptLevel > 2)
return InlineConstants::OptAggressiveThreshold;
if (SizeOptLevel == 1) // -Os
return InlineConstants::OptSizeThreshold;
if (SizeOptLevel == 2) // -Oz
return InlineConstants::OptMinSizeThreshold;
return InlineThreshold;
}
InlineParams llvm::getInlineParams(unsigned OptLevel, unsigned SizeOptLevel) {
auto Params =
getInlineParams(computeThresholdFromOptLevels(OptLevel, SizeOptLevel));
// At O3, use the value of -locally-hot-callsite-threshold option to populate
// Params.LocallyHotCallSiteThreshold. Below O3, this flag has effect only
// when it is specified explicitly.
if (OptLevel > 2)
Params.LocallyHotCallSiteThreshold = LocallyHotCallSiteThreshold;
return Params;
}
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