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llvm-mirror/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/Support/CallSite.h"
#include "llvm/CallingConv.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace llvm;
// CountCodeReductionForConstant - Figure out an approximation for how many
// instructions will be constant folded if the specified value is constant.
//
unsigned InlineCostAnalyzer::FunctionInfo::
CountCodeReductionForConstant(Value *V) {
unsigned Reduction = 0;
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[TI.getSuccessor(I)];
// We don't know which blocks will be eliminated, so use the average size.
Reduction += InlineConstants::InstrCost*Instrs*(NumSucc-1)/NumSucc;
} else if (CallInst *CI = dyn_cast<CallInst>(U)) {
// Turning an indirect call into a direct call is a BIG win
if (CI->getCalledValue() == V)
Reduction += InlineConstants::IndirectCallBonus;
} else if (InvokeInst *II = dyn_cast<InvokeInst>(U)) {
// Turning an indirect call into a direct call is a BIG win
if (II->getCalledValue() == V)
Reduction += InlineConstants::IndirectCallBonus;
} else {
// 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) {
// We will get to remove this instruction...
Reduction += InlineConstants::InstrCost;
// And any other instructions that use it which become constants
// themselves.
Reduction += CountCodeReductionForConstant(&Inst);
}
}
}
return Reduction;
}
// CountCodeReductionForAlloca - Figure out an approximation of how much smaller
// the function will be if it is inlined into a context where an argument
// becomes an alloca.
//
unsigned InlineCostAnalyzer::FunctionInfo::
CountCodeReductionForAlloca(Value *V) {
if (!V->getType()->isPointerTy()) return 0; // Not a pointer
unsigned Reduction = 0;
for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
Instruction *I = cast<Instruction>(*UI);
if (isa<LoadInst>(I) || isa<StoreInst>(I))
Reduction += InlineConstants::InstrCost;
else 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())
Reduction += CountCodeReductionForAlloca(GEP);
} else if (BitCastInst *BCI = dyn_cast<BitCastInst>(I)) {
// Track pointer through bitcasts.
Reduction += CountCodeReductionForAlloca(BCI);
} else {
// If there is some other strange instruction, we're not going to be able
// to do much if we inline this.
return 0;
}
}
return Reduction;
}
/// 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) {
++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 (isa<DbgInfoIntrinsic>(II))
continue; // Debug intrinsics don't count as size.
CallSite CS = CallSite::get(const_cast<Instruction*>(&*II));
// If this function contains a call to setjmp or _setjmp, 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.
if (Function *F = CS.getCalledFunction()) {
if (F->isDeclaration() &&
(F->getName() == "setjmp" || F->getName() == "_setjmp"))
callsSetJmp = true;
// 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;
// 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.
if (isa<IndirectBrInst>(BB->getTerminator()))
containsIndirectBr = true;
// Remember NumInsts for this BB.
NumBBInsts[BB] = NumInsts - NumInstsBeforeThisBB;
}
/// analyzeFunction - Fill in the current structure with information gleaned
/// from the specified function.
void CodeMetrics::analyzeFunction(Function *F) {
// Look at the size of the callee.
for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
analyzeBasicBlock(&*BB);
}
/// analyzeFunction - Fill in the current structure with information gleaned
/// from the specified function.
void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) {
Metrics.analyzeFunction(F);
// 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;
// Don't bother calculating argument weights if we are never going to inline
// the function anyway.
if (NeverInline())
return;
// Check out all of the arguments to the function, figuring out how much
// code can be eliminated if one of the arguments is a constant.
ArgumentWeights.reserve(F->arg_size());
for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I),
CountCodeReductionForAlloca(I)));
}
/// NeverInline - returns true if the function should never be inlined into
/// any caller
bool InlineCostAnalyzer::FunctionInfo::NeverInline()
{
return (Metrics.callsSetJmp || Metrics.isRecursive ||
Metrics.containsIndirectBr);
}
// 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();
bool isDirectCall = CS.getCalledFunction() == Callee;
// 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();
// 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;
// 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)
InlineCost += InlineConstants::LastCallToStaticBonus;
// If this function uses the coldcc calling convention, prefer not to inline
// it.
if (Callee->getCallingConv() == CallingConv::Cold)
InlineCost += InlineConstants::ColdccPenalty;
// 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()))
InlineCost += InlineConstants::NoreturnPenalty;
} else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall)))
InlineCost += InlineConstants::NoreturnPenalty;
// 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);
// 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 infomation 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);
// 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();
}
// 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.
//
unsigned ArgNo = 0;
for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I, ++ArgNo) {
// 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 -= InlineConstants::InstrCost;
// 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)) {
if (ArgNo < CalleeFI->ArgumentWeights.size())
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)) {
if (ArgNo < CalleeFI->ArgumentWeights.size())
InlineCost -= CalleeFI->ArgumentWeights[ArgNo].ConstantWeight;
}
}
// 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 llvm::InlineCost::get(InlineCost);
}
// 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);
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.callsSetJmp |= CalleeMetrics.callsSetJmp;
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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