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llvm-mirror/lib/Analysis/InlineCost.cpp
Chandler Carruth 889ecbc0f8 Extend the inline cost calculation to account for bonuses due to 
correlated pairs of pointer arguments at the callsite. This is designed
to recognize the common C++ idiom of begin/end pointer pairs when the
end pointer is a constant offset from the begin pointer. With the
C-based idiom of a pointer and size, the inline cost saw the constant
size calculation, and this provides the same level of information for
begin/end pairs.

In order to propagate this information we have to search for candidate
operations on a pair of pointer function arguments (or derived from
them) which would be simplified if the pointers had a known constant
offset. Then the callsite analysis looks for such pointer pairs in the
argument list, and applies the appropriate bonus.

This helps LLVM detect that half of bounds-checked STL algorithms
(such as hash_combine_range, and some hybrid sort implementations)
disappear when inlined with a constant size input. However, it's not
a complete fix due the inaccuracy of our cost metric for constants in
general. I'm looking into that next.

Benchmarks showed no significant code size change, and very minor
performance changes. However, specific code such as hashing is showing
significantly cleaner inlining decisions.

llvm-svn: 152752
2012-03-14 23:19:53 +00:00

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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/Support/CallSite.h"
#include "llvm/CallingConv.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace llvm;
/// callIsSmall - If a call is likely to lower to a single target instruction,
/// or is otherwise deemed small return true.
/// TODO: Perhaps calls like memcpy, strcpy, etc?
bool llvm::callIsSmall(const Function *F) {
if (!F) return false;
if (F->hasLocalLinkage()) return false;
if (!F->hasName()) return false;
StringRef Name = F->getName();
// These will all likely lower to a single selection DAG node.
if (Name == "copysign" || Name == "copysignf" || Name == "copysignl" ||
Name == "fabs" || Name == "fabsf" || Name == "fabsl" ||
Name == "sin" || Name == "sinf" || Name == "sinl" ||
Name == "cos" || Name == "cosf" || Name == "cosl" ||
Name == "sqrt" || Name == "sqrtf" || Name == "sqrtl" )
return true;
// These are all likely to be optimized into something smaller.
if (Name == "pow" || Name == "powf" || Name == "powl" ||
Name == "exp2" || Name == "exp2l" || Name == "exp2f" ||
Name == "floor" || Name == "floorf" || Name == "ceil" ||
Name == "round" || Name == "ffs" || Name == "ffsl" ||
Name == "abs" || Name == "labs" || Name == "llabs")
return true;
return false;
}
/// analyzeBasicBlock - Fill in the current structure with information gleaned
/// from the specified block.
void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB,
const TargetData *TD) {
++NumBlocks;
unsigned NumInstsBeforeThisBB = NumInsts;
for (BasicBlock::const_iterator II = BB->begin(), E = BB->end();
II != E; ++II) {
if (isa<PHINode>(II)) continue; // PHI nodes don't count.
// Special handling for calls.
if (isa<CallInst>(II) || isa<InvokeInst>(II)) {
if (const IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(II)) {
switch (IntrinsicI->getIntrinsicID()) {
default: break;
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::objectsize:
case Intrinsic::ptr_annotation:
case Intrinsic::var_annotation:
// These intrinsics don't count as size.
continue;
}
}
ImmutableCallSite CS(cast<Instruction>(II));
if (const Function *F = CS.getCalledFunction()) {
// If a function is both internal and has a single use, then it is
// extremely likely to get inlined in the future (it was probably
// exposed by an interleaved devirtualization pass).
if (!CS.isNoInline() && F->hasInternalLinkage() && F->hasOneUse())
++NumInlineCandidates;
// If this call is to function itself, then the function is recursive.
// Inlining it into other functions is a bad idea, because this is
// basically just a form of loop peeling, and our metrics aren't useful
// for that case.
if (F == BB->getParent())
isRecursive = true;
}
if (!isa<IntrinsicInst>(II) && !callIsSmall(CS.getCalledFunction())) {
// Each argument to a call takes on average one instruction to set up.
NumInsts += CS.arg_size();
// We don't want inline asm to count as a call - that would prevent loop
// unrolling. The argument setup cost is still real, though.
if (!isa<InlineAsm>(CS.getCalledValue()))
++NumCalls;
}
}
if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
if (!AI->isStaticAlloca())
this->usesDynamicAlloca = true;
}
if (isa<ExtractElementInst>(II) || II->getType()->isVectorTy())
++NumVectorInsts;
if (const CastInst *CI = dyn_cast<CastInst>(II)) {
// Noop casts, including ptr <-> int, don't count.
if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) ||
isa<PtrToIntInst>(CI))
continue;
// trunc to a native type is free (assuming the target has compare and
// shift-right of the same width).
if (isa<TruncInst>(CI) && TD &&
TD->isLegalInteger(TD->getTypeSizeInBits(CI->getType())))
continue;
// Result of a cmp instruction is often extended (to be used by other
// cmp instructions, logical or return instructions). These are usually
// nop on most sane targets.
if (isa<CmpInst>(CI->getOperand(0)))
continue;
} else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(II)){
// If a GEP has all constant indices, it will probably be folded with
// a load/store.
if (GEPI->hasAllConstantIndices())
continue;
}
++NumInsts;
}
if (isa<ReturnInst>(BB->getTerminator()))
++NumRets;
// 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. And as a QOI issue,
// if someone is using a blockaddress without an indirectbr, and that
// reference somehow ends up in another function or global, we probably
// don't want to inline this function.
if (isa<IndirectBrInst>(BB->getTerminator()))
containsIndirectBr = true;
// Remember NumInsts for this BB.
NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
}
unsigned InlineCostAnalyzer::FunctionInfo::countCodeReductionForConstant(
const CodeMetrics &Metrics, Value *V) {
unsigned Reduction = 0;
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
do {
Value *V = Worklist.pop_back_val();
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
User *U = *UI;
if (isa<BranchInst>(U) || isa<SwitchInst>(U)) {
// We will be able to eliminate all but one of the successors.
const TerminatorInst &TI = cast<TerminatorInst>(*U);
const unsigned NumSucc = TI.getNumSuccessors();
unsigned Instrs = 0;
for (unsigned I = 0; I != NumSucc; ++I)
Instrs += Metrics.NumBBInsts.lookup(TI.getSuccessor(I));
// We don't know which blocks will be eliminated, so use the average size.
Reduction += InlineConstants::InstrCost*Instrs*(NumSucc-1)/NumSucc;
continue;
}
// Figure out if this instruction will be removed due to simple constant
// propagation.
Instruction &Inst = cast<Instruction>(*U);
// We can't constant propagate instructions which have effects or
// read memory.
//
// FIXME: It would be nice to capture the fact that a load from a
// pointer-to-constant-global is actually a *really* good thing to zap.
// Unfortunately, we don't know the pointer that may get propagated here,
// so we can't make this decision.
if (Inst.mayReadFromMemory() || Inst.mayHaveSideEffects() ||
isa<AllocaInst>(Inst))
continue;
bool AllOperandsConstant = true;
for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) {
AllOperandsConstant = false;
break;
}
if (!AllOperandsConstant)
continue;
// We will get to remove this instruction...
Reduction += InlineConstants::InstrCost;
// And any other instructions that use it which become constants
// themselves.
Worklist.push_back(&Inst);
}
} while (!Worklist.empty());
return Reduction;
}
static unsigned countCodeReductionForAllocaICmp(const CodeMetrics &Metrics,
ICmpInst *ICI) {
unsigned Reduction = 0;
// Bail if this is comparing against a non-constant; there is nothing we can
// do there.
if (!isa<Constant>(ICI->getOperand(1)))
return Reduction;
// An icmp pred (alloca, C) becomes true if the predicate is true when
// equal and false otherwise.
bool Result = ICI->isTrueWhenEqual();
SmallVector<Instruction *, 4> Worklist;
Worklist.push_back(ICI);
do {
Instruction *U = Worklist.pop_back_val();
Reduction += InlineConstants::InstrCost;
for (Value::use_iterator UI = U->use_begin(), UE = U->use_end();
UI != UE; ++UI) {
Instruction *I = dyn_cast<Instruction>(*UI);
if (!I || I->mayHaveSideEffects()) continue;
if (I->getNumOperands() == 1)
Worklist.push_back(I);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
// If BO produces the same value as U, then the other operand is
// irrelevant and we can put it into the Worklist to continue
// deleting dead instructions. If BO produces the same value as the
// other operand, we can delete BO but that's it.
if (Result == true) {
if (BO->getOpcode() == Instruction::Or)
Worklist.push_back(I);
if (BO->getOpcode() == Instruction::And)
Reduction += InlineConstants::InstrCost;
} else {
if (BO->getOpcode() == Instruction::Or ||
BO->getOpcode() == Instruction::Xor)
Reduction += InlineConstants::InstrCost;
if (BO->getOpcode() == Instruction::And)
Worklist.push_back(I);
}
}
if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
BasicBlock *BB = BI->getSuccessor(Result ? 0 : 1);
if (BB->getSinglePredecessor())
Reduction
+= InlineConstants::InstrCost * Metrics.NumBBInsts.lookup(BB);
}
}
} while (!Worklist.empty());
return Reduction;
}
/// \brief Compute the reduction possible for a given instruction if we are able
/// to SROA an alloca.
///
/// The reduction for this instruction is added to the SROAReduction output
/// parameter. Returns false if this instruction is expected to defeat SROA in
/// general.
static bool countCodeReductionForSROAInst(Instruction *I,
SmallVectorImpl<Value *> &Worklist,
unsigned &SROAReduction) {
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (!LI->isSimple())
return false;
SROAReduction += InlineConstants::InstrCost;
return true;
}
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
if (!SI->isSimple())
return false;
SROAReduction += InlineConstants::InstrCost;
return true;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
// If the GEP has variable indices, we won't be able to do much with it.
if (!GEP->hasAllConstantIndices())
return false;
// A non-zero GEP will likely become a mask operation after SROA.
if (GEP->hasAllZeroIndices())
SROAReduction += InlineConstants::InstrCost;
Worklist.push_back(GEP);
return true;
}
if (BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
// Track pointer through bitcasts.
Worklist.push_back(BCI);
SROAReduction += InlineConstants::InstrCost;
return true;
}
// We just look for non-constant operands to ICmp instructions as those will
// defeat SROA. The actual reduction for these happens even without SROA.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
return isa<Constant>(ICI->getOperand(1));
if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
// SROA can handle a select of alloca iff all uses of the alloca are
// loads, and dereferenceable. We assume it's dereferenceable since
// we're told the input is an alloca.
for (Value::use_iterator UI = SI->use_begin(), UE = SI->use_end();
UI != UE; ++UI) {
LoadInst *LI = dyn_cast<LoadInst>(*UI);
if (LI == 0 || !LI->isSimple())
return false;
}
// We don't know whether we'll be deleting the rest of the chain of
// instructions from the SelectInst on, because we don't know whether
// the other side of the select is also an alloca or not.
return true;
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
return false;
case Intrinsic::memset:
case Intrinsic::memcpy:
case Intrinsic::memmove:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
// SROA can usually chew through these intrinsics.
SROAReduction += InlineConstants::InstrCost;
return true;
}
}
// If there is some other strange instruction, we're not going to be
// able to do much if we inline this.
return false;
}
unsigned InlineCostAnalyzer::FunctionInfo::countCodeReductionForAlloca(
const CodeMetrics &Metrics, Value *V) {
if (!V->getType()->isPointerTy()) return 0; // Not a pointer
unsigned Reduction = 0;
unsigned SROAReduction = 0;
bool CanSROAAlloca = true;
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
do {
Value *V = Worklist.pop_back_val();
for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI){
Instruction *I = cast<Instruction>(*UI);
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
Reduction += countCodeReductionForAllocaICmp(Metrics, ICI);
if (CanSROAAlloca)
CanSROAAlloca = countCodeReductionForSROAInst(I, Worklist,
SROAReduction);
}
} while (!Worklist.empty());
return Reduction + (CanSROAAlloca ? SROAReduction : 0);
}
void InlineCostAnalyzer::FunctionInfo::countCodeReductionForPointerPair(
const CodeMetrics &Metrics, DenseMap<Value *, unsigned> &PointerArgs,
Value *V, unsigned ArgIdx) {
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
do {
Value *V = Worklist.pop_back_val();
for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI){
Instruction *I = cast<Instruction>(*UI);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
// If the GEP has variable indices, we won't be able to do much with it.
if (!GEP->hasAllConstantIndices())
continue;
// Unless the GEP is in-bounds, some comparisons will be non-constant.
// Fortunately, the real-world cases where this occurs uses in-bounds
// GEPs, and so we restrict the optimization to them here.
if (!GEP->isInBounds())
continue;
// Constant indices just change the constant offset. Add the resulting
// value both to our worklist for this argument, and to the set of
// viable paired values with future arguments.
PointerArgs[GEP] = ArgIdx;
Worklist.push_back(GEP);
continue;
}
// Track pointer through casts. Even when the result is not a pointer, it
// remains a constant relative to constants derived from other constant
// pointers.
if (CastInst *CI = dyn_cast<CastInst>(I)) {
PointerArgs[CI] = ArgIdx;
Worklist.push_back(CI);
continue;
}
// There are two instructions which produce a strict constant value when
// applied to two related pointer values. Ignore everything else.
if (!isa<ICmpInst>(I) && I->getOpcode() != Instruction::Sub)
continue;
assert(I->getNumOperands() == 2);
// Ensure that the two operands are in our set of potentially paired
// pointers (or are derived from them).
Value *OtherArg = I->getOperand(0);
if (OtherArg == V)
OtherArg = I->getOperand(1);
DenseMap<Value *, unsigned>::const_iterator ArgIt
= PointerArgs.find(OtherArg);
if (ArgIt == PointerArgs.end())
continue;
assert(ArgIt->second < ArgIdx);
PointerArgPairWeights[std::make_pair(ArgIt->second, ArgIdx)]
+= countCodeReductionForConstant(Metrics, I);
}
} while (!Worklist.empty());
}
/// analyzeFunction - Fill in the current structure with information gleaned
/// from the specified function.
void CodeMetrics::analyzeFunction(Function *F, const TargetData *TD) {
// If this function contains a call that "returns twice" (e.g., setjmp or
// _setjmp) and it isn't marked with "returns twice" itself, never inline it.
// This is a hack because we depend on the user marking their local variables
// as volatile if they are live across a setjmp call, and they probably
// won't do this in callers.
exposesReturnsTwice = F->callsFunctionThatReturnsTwice() &&
!F->hasFnAttr(Attribute::ReturnsTwice);
// Look at the size of the callee.
for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
analyzeBasicBlock(&*BB, TD);
}
/// analyzeFunction - Fill in the current structure with information gleaned
/// from the specified function.
void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F,
const TargetData *TD) {
Metrics.analyzeFunction(F, TD);
// A function with exactly one return has it removed during the inlining
// process (see InlineFunction), so don't count it.
// FIXME: This knowledge should really be encoded outside of FunctionInfo.
if (Metrics.NumRets==1)
--Metrics.NumInsts;
ArgumentWeights.reserve(F->arg_size());
DenseMap<Value *, unsigned> PointerArgs;
unsigned ArgIdx = 0;
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
++I, ++ArgIdx) {
// Count how much code can be eliminated if one of the arguments is
// a constant or an alloca.
ArgumentWeights.push_back(ArgInfo(countCodeReductionForConstant(Metrics, I),
countCodeReductionForAlloca(Metrics, I)));
// If the argument is a pointer, also check for pairs of pointers where
// knowing a fixed offset between them allows simplification. This pattern
// arises mostly due to STL algorithm patterns where pointers are used as
// random access iterators.
if (!I->getType()->isPointerTy())
continue;
PointerArgs[I] = ArgIdx;
countCodeReductionForPointerPair(Metrics, PointerArgs, I, ArgIdx);
}
}
/// NeverInline - returns true if the function should never be inlined into
/// any caller
bool InlineCostAnalyzer::FunctionInfo::NeverInline() {
return (Metrics.exposesReturnsTwice || Metrics.isRecursive ||
Metrics.containsIndirectBr);
}
// getSpecializationBonus - The heuristic used to determine the per-call
// performance boost for using a specialization of Callee with argument
// specializedArgNo replaced by a constant.
int InlineCostAnalyzer::getSpecializationBonus(Function *Callee,
SmallVectorImpl<unsigned> &SpecializedArgNos)
{
if (Callee->mayBeOverridden())
return 0;
int Bonus = 0;
// If this function uses the coldcc calling convention, prefer not to
// specialize it.
if (Callee->getCallingConv() == CallingConv::Cold)
Bonus -= InlineConstants::ColdccPenalty;
// Get information about the callee.
FunctionInfo *CalleeFI = &CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI->Metrics.NumBlocks == 0)
CalleeFI->analyzeFunction(Callee, TD);
unsigned ArgNo = 0;
unsigned i = 0;
for (Function::arg_iterator I = Callee->arg_begin(), E = Callee->arg_end();
I != E; ++I, ++ArgNo)
if (ArgNo == SpecializedArgNos[i]) {
++i;
Bonus += CountBonusForConstant(I);
}
// Calls usually take a long time, so they make the specialization gain
// smaller.
Bonus -= CalleeFI->Metrics.NumCalls * InlineConstants::CallPenalty;
return Bonus;
}
// ConstantFunctionBonus - Figure out how much of a bonus we can get for
// possibly devirtualizing a function. We'll subtract the size of the function
// we may wish to inline from the indirect call bonus providing a limit on
// growth. Leave an upper limit of 0 for the bonus - we don't want to penalize
// inlining because we decide we don't want to give a bonus for
// devirtualizing.
int InlineCostAnalyzer::ConstantFunctionBonus(CallSite CS, Constant *C) {
// This could just be NULL.
if (!C) return 0;
Function *F = dyn_cast<Function>(C);
if (!F) return 0;
int Bonus = InlineConstants::IndirectCallBonus + getInlineSize(CS, F);
return (Bonus > 0) ? 0 : Bonus;
}
// CountBonusForConstant - Figure out an approximation for how much per-call
// performance boost we can expect if the specified value is constant.
int InlineCostAnalyzer::CountBonusForConstant(Value *V, Constant *C) {
unsigned Bonus = 0;
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
User *U = *UI;
if (CallInst *CI = dyn_cast<CallInst>(U)) {
// Turning an indirect call into a direct call is a BIG win
if (CI->getCalledValue() == V)
Bonus += ConstantFunctionBonus(CallSite(CI), C);
} else if (InvokeInst *II = dyn_cast<InvokeInst>(U)) {
// Turning an indirect call into a direct call is a BIG win
if (II->getCalledValue() == V)
Bonus += ConstantFunctionBonus(CallSite(II), C);
}
// FIXME: Eliminating conditional branches and switches should
// also yield a per-call performance boost.
else {
// Figure out the bonuses that wll accrue due to simple constant
// propagation.
Instruction &Inst = cast<Instruction>(*U);
// We can't constant propagate instructions which have effects or
// read memory.
//
// FIXME: It would be nice to capture the fact that a load from a
// pointer-to-constant-global is actually a *really* good thing to zap.
// Unfortunately, we don't know the pointer that may get propagated here,
// so we can't make this decision.
if (Inst.mayReadFromMemory() || Inst.mayHaveSideEffects() ||
isa<AllocaInst>(Inst))
continue;
bool AllOperandsConstant = true;
for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) {
AllOperandsConstant = false;
break;
}
if (AllOperandsConstant)
Bonus += CountBonusForConstant(&Inst);
}
}
return Bonus;
}
int InlineCostAnalyzer::getInlineSize(CallSite CS, Function *Callee) {
// Get information about the callee.
FunctionInfo *CalleeFI = &CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI->Metrics.NumBlocks == 0)
CalleeFI->analyzeFunction(Callee, TD);
// InlineCost - This value measures how good of an inline candidate this call
// site is to inline. A lower inline cost make is more likely for the call to
// be inlined. This value may go negative.
//
int InlineCost = 0;
// Compute any size reductions we can expect due to arguments being passed into
// the function.
//
unsigned ArgNo = 0;
CallSite::arg_iterator I = CS.arg_begin();
for (Function::arg_iterator FI = Callee->arg_begin(), FE = Callee->arg_end();
FI != FE; ++I, ++FI, ++ArgNo) {
// If an alloca is passed in, inlining this function is likely to allow
// significant future optimization possibilities (like scalar promotion, and
// scalarization), so encourage the inlining of the function.
//
if (isa<AllocaInst>(I))
InlineCost -= CalleeFI->ArgumentWeights[ArgNo].AllocaWeight;
// If this is a constant being passed into the function, use the argument
// weights calculated for the callee to determine how much will be folded
// away with this information.
else if (isa<Constant>(I))
InlineCost -= CalleeFI->ArgumentWeights[ArgNo].ConstantWeight;
}
const DenseMap<std::pair<unsigned, unsigned>, unsigned> &ArgPairWeights
= CalleeFI->PointerArgPairWeights;
for (DenseMap<std::pair<unsigned, unsigned>, unsigned>::const_iterator I
= ArgPairWeights.begin(), E = ArgPairWeights.end();
I != E; ++I)
if (CS.getArgument(I->first.first)->stripInBoundsConstantOffsets() ==
CS.getArgument(I->first.second)->stripInBoundsConstantOffsets())
InlineCost -= I->second;
// Each argument passed in has a cost at both the caller and the callee
// sides. Measurements show that each argument costs about the same as an
// instruction.
InlineCost -= (CS.arg_size() * InlineConstants::InstrCost);
// Now that we have considered all of the factors that make the call site more
// likely to be inlined, look at factors that make us not want to inline it.
// Calls usually take a long time, so they make the inlining gain smaller.
InlineCost += CalleeFI->Metrics.NumCalls * InlineConstants::CallPenalty;
// Look at the size of the callee. Each instruction counts as 5.
InlineCost += CalleeFI->Metrics.NumInsts * InlineConstants::InstrCost;
return InlineCost;
}
int InlineCostAnalyzer::getInlineBonuses(CallSite CS, Function *Callee) {
// Get information about the callee.
FunctionInfo *CalleeFI = &CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI->Metrics.NumBlocks == 0)
CalleeFI->analyzeFunction(Callee, TD);
bool isDirectCall = CS.getCalledFunction() == Callee;
Instruction *TheCall = CS.getInstruction();
int Bonus = 0;
// If there is only one call of the function, and it has internal linkage,
// make it almost guaranteed to be inlined.
//
if (Callee->hasLocalLinkage() && Callee->hasOneUse() && isDirectCall)
Bonus += InlineConstants::LastCallToStaticBonus;
// If the instruction after the call, or if the normal destination of the
// invoke is an unreachable instruction, the function is noreturn. As such,
// there is little point in inlining this.
if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) {
if (isa<UnreachableInst>(II->getNormalDest()->begin()))
Bonus += InlineConstants::NoreturnPenalty;
} else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
Bonus += InlineConstants::NoreturnPenalty;
// If this function uses the coldcc calling convention, prefer not to inline
// it.
if (Callee->getCallingConv() == CallingConv::Cold)
Bonus += InlineConstants::ColdccPenalty;
// Add to the inline quality for properties that make the call valuable to
// inline. This includes factors that indicate that the result of inlining
// the function will be optimizable. Currently this just looks at arguments
// passed into the function.
//
CallSite::arg_iterator I = CS.arg_begin();
for (Function::arg_iterator FI = Callee->arg_begin(), FE = Callee->arg_end();
FI != FE; ++I, ++FI)
// Compute any constant bonus due to inlining we want to give here.
if (isa<Constant>(I))
Bonus += CountBonusForConstant(FI, cast<Constant>(I));
return Bonus;
}
// getInlineCost - The heuristic used to determine if we should inline the
// function call or not.
//
InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
SmallPtrSet<const Function*, 16> &NeverInline) {
return getInlineCost(CS, CS.getCalledFunction(), NeverInline);
}
InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
Function *Callee,
SmallPtrSet<const Function*, 16> &NeverInline) {
Instruction *TheCall = CS.getInstruction();
Function *Caller = TheCall->getParent()->getParent();
// Don't inline functions which can be redefined at link-time to mean
// something else. Don't inline functions marked noinline or call sites
// marked noinline.
if (Callee->mayBeOverridden() ||
Callee->hasFnAttr(Attribute::NoInline) || NeverInline.count(Callee) ||
CS.isNoInline())
return llvm::InlineCost::getNever();
// Get information about the callee.
FunctionInfo *CalleeFI = &CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI->Metrics.NumBlocks == 0)
CalleeFI->analyzeFunction(Callee, TD);
// If we should never inline this, return a huge cost.
if (CalleeFI->NeverInline())
return InlineCost::getNever();
// FIXME: It would be nice to kill off CalleeFI->NeverInline. Then we
// could move this up and avoid computing the FunctionInfo for
// things we are going to just return always inline for. This
// requires handling setjmp somewhere else, however.
if (!Callee->isDeclaration() && Callee->hasFnAttr(Attribute::AlwaysInline))
return InlineCost::getAlways();
if (CalleeFI->Metrics.usesDynamicAlloca) {
// Get information about the caller.
FunctionInfo &CallerFI = CachedFunctionInfo[Caller];
// If we haven't calculated this information yet, do so now.
if (CallerFI.Metrics.NumBlocks == 0) {
CallerFI.analyzeFunction(Caller, TD);
// Recompute the CalleeFI pointer, getting Caller could have invalidated
// it.
CalleeFI = &CachedFunctionInfo[Callee];
}
// Don't inline a callee with dynamic alloca into a caller without them.
// Functions containing dynamic alloca's are inefficient in various ways;
// don't create more inefficiency.
if (!CallerFI.Metrics.usesDynamicAlloca)
return InlineCost::getNever();
}
// InlineCost - This value measures how good of an inline candidate this call
// site is to inline. A lower inline cost make is more likely for the call to
// be inlined. This value may go negative due to the fact that bonuses
// are negative numbers.
//
int InlineCost = getInlineSize(CS, Callee) + getInlineBonuses(CS, Callee);
return llvm::InlineCost::get(InlineCost);
}
// getSpecializationCost - The heuristic used to determine the code-size
// impact of creating a specialized version of Callee with argument
// SpecializedArgNo replaced by a constant.
InlineCost InlineCostAnalyzer::getSpecializationCost(Function *Callee,
SmallVectorImpl<unsigned> &SpecializedArgNos)
{
// Don't specialize functions which can be redefined at link-time to mean
// something else.
if (Callee->mayBeOverridden())
return llvm::InlineCost::getNever();
// Get information about the callee.
FunctionInfo *CalleeFI = &CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI->Metrics.NumBlocks == 0)
CalleeFI->analyzeFunction(Callee, TD);
int Cost = 0;
// Look at the original size of the callee. Each instruction counts as 5.
Cost += CalleeFI->Metrics.NumInsts * InlineConstants::InstrCost;
// Offset that with the amount of code that can be constant-folded
// away with the given arguments replaced by constants.
for (SmallVectorImpl<unsigned>::iterator an = SpecializedArgNos.begin(),
ae = SpecializedArgNos.end(); an != ae; ++an)
Cost -= CalleeFI->ArgumentWeights[*an].ConstantWeight;
return llvm::InlineCost::get(Cost);
}
// getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a
// higher threshold to determine if the function call should be inlined.
float InlineCostAnalyzer::getInlineFudgeFactor(CallSite CS) {
Function *Callee = CS.getCalledFunction();
// Get information about the callee.
FunctionInfo &CalleeFI = CachedFunctionInfo[Callee];
// If we haven't calculated this information yet, do so now.
if (CalleeFI.Metrics.NumBlocks == 0)
CalleeFI.analyzeFunction(Callee, TD);
float Factor = 1.0f;
// Single BB functions are often written to be inlined.
if (CalleeFI.Metrics.NumBlocks == 1)
Factor += 0.5f;
// Be more aggressive if the function contains a good chunk (if it mades up
// at least 10% of the instructions) of vector instructions.
if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/2)
Factor += 2.0f;
else if (CalleeFI.Metrics.NumVectorInsts > CalleeFI.Metrics.NumInsts/10)
Factor += 1.5f;
return Factor;
}
/// growCachedCostInfo - update the cached cost info for Caller after Callee has
/// been inlined.
void
InlineCostAnalyzer::growCachedCostInfo(Function *Caller, Function *Callee) {
CodeMetrics &CallerMetrics = CachedFunctionInfo[Caller].Metrics;
// For small functions we prefer to recalculate the cost for better accuracy.
if (CallerMetrics.NumBlocks < 10 && CallerMetrics.NumInsts < 1000) {
resetCachedCostInfo(Caller);
return;
}
// For large functions, we can save a lot of computation time by skipping
// recalculations.
if (CallerMetrics.NumCalls > 0)
--CallerMetrics.NumCalls;
if (Callee == 0) return;
CodeMetrics &CalleeMetrics = CachedFunctionInfo[Callee].Metrics;
// If we don't have metrics for the callee, don't recalculate them just to
// update an approximation in the caller. Instead, just recalculate the
// caller info from scratch.
if (CalleeMetrics.NumBlocks == 0) {
resetCachedCostInfo(Caller);
return;
}
// Since CalleeMetrics were already calculated, we know that the CallerMetrics
// reference isn't invalidated: both were in the DenseMap.
CallerMetrics.usesDynamicAlloca |= CalleeMetrics.usesDynamicAlloca;
// FIXME: If any of these three are true for the callee, the callee was
// not inlined into the caller, so I think they're redundant here.
CallerMetrics.exposesReturnsTwice |= CalleeMetrics.exposesReturnsTwice;
CallerMetrics.isRecursive |= CalleeMetrics.isRecursive;
CallerMetrics.containsIndirectBr |= CalleeMetrics.containsIndirectBr;
CallerMetrics.NumInsts += CalleeMetrics.NumInsts;
CallerMetrics.NumBlocks += CalleeMetrics.NumBlocks;
CallerMetrics.NumCalls += CalleeMetrics.NumCalls;
CallerMetrics.NumVectorInsts += CalleeMetrics.NumVectorInsts;
CallerMetrics.NumRets += CalleeMetrics.NumRets;
// analyzeBasicBlock counts each function argument as an inst.
if (CallerMetrics.NumInsts >= Callee->arg_size())
CallerMetrics.NumInsts -= Callee->arg_size();
else
CallerMetrics.NumInsts = 0;
// We are not updating the argument weights. We have already determined that
// Caller is a fairly large function, so we accept the loss of precision.
}
/// clear - empty the cache of inline costs
void InlineCostAnalyzer::clear() {
CachedFunctionInfo.clear();
}
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