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Rewrite how the indirect call bonus is handled. This now works by:

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a) Making it a per call site bonus for functions that we can move from
indirect to direct calls.
b) Reduces the bonus from 500 to 100 per call site.
c) Subtracts the size of the possible newly inlineable call from the
bonus to only add a bonus if we can inline a small function to devirtualize
it.

Also changes the bonus from a positive that's subtracted to a negative
that's added.

Fixes the remainder of rdar://8546196 by reducing the object file size
after inlining by 84%.

llvm-svn: 124916
This commit is contained in:
Eric Christopher 2011-02-05 00:49:15 +00:00
parent 50efbf730f
commit ddc2157034
2 changed files with 130 additions and 80 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/llvm/Analysis/InlineCost.h
View File

@ -33,7 +33,7 @@ namespace llvm {
namespace InlineConstants {
// Various magic constants used to adjust heuristics.
const int InstrCost = 5;
const int IndirectCallBonus = 500;
const int IndirectCallBonus = -100;
const int CallPenalty = 25;
const int LastCallToStaticBonus = -15000;
const int ColdccPenalty = 2000;
@ -124,7 +124,10 @@ namespace llvm {
// the ValueMap will update itself when this happens.
ValueMap<const Function *, FunctionInfo> CachedFunctionInfo;
unsigned CountBonusForConstant(Value *V);
int CountBonusForConstant(Value *V, Constant *C = NULL);
int ConstantFunctionBonus(CallSite CS, Constant *C);
int getInlineSize(CallSite CS, Function *Callee);
int getInlineBonuses(CallSite CS, Function *Callee);
public:
/// getInlineCost - The heuristic used to determine if we should inline the

203
lib/Analysis/InlineCost.cpp
View File

@ -16,6 +16,7 @@
#include "llvm/CallingConv.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace llvm;
/// callIsSmall - If a call is likely to lower to a single target instruction,
@ -298,22 +299,38 @@ int InlineCostAnalyzer::getSpecializationBonus(Function *Callee,
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.
unsigned InlineCostAnalyzer::CountBonusForConstant(Value *V) {
int InlineCostAnalyzer::CountBonusForConstant(Value *V, Constant *C) {
unsigned Bonus = 0;
bool indirectCallBonus = false;
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)
indirectCallBonus = true;
}
else if (InvokeInst *II = dyn_cast<InvokeInst>(U)) {
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)
indirectCallBonus = true;
Bonus += ConstantFunctionBonus(CallSite(CI), C);
}
// FIXME: Eliminating conditional branches and switches should
// also yield a per-call performance boost.
@ -345,13 +362,106 @@ unsigned InlineCostAnalyzer::CountBonusForConstant(Value *V) {
}
}
// FIXME: The only reason we're applying the bonus once is while it's great
// to devirtualize calls the magnitude of the bonus x number of call sites
// can lead to a huge code explosion when we prefer to inline 1000 instruction
// functions that have 10 call sites. This should be made a function of the
// estimated inline penalty/benefit + the indirect call bonus.
if (indirectCallBonus) Bonus += InlineConstants::IndirectCallBonus;
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);
// 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;
}
// 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);
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;
}
@ -368,7 +478,6 @@ InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
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
@ -418,72 +527,10 @@ InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
// 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.
// be inlined. This value may go negative due to the fact that bonuses
// are negative numbers.
//
int InlineCost = 0;
// 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;
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;
// Compute any constant bonus due to inlining we want to give here.
InlineCost -= CountBonusForConstant(FI);
}
}
// 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);
// 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;
// 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.
// 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;
// If this function uses the coldcc calling convention, prefer not to inline
// it.
if (Callee->getCallingConv() == CallingConv::Cold)
InlineCost += InlineConstants::ColdccPenalty;
// 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;
int InlineCost = getInlineSize(CS, Callee) + getInlineBonuses(CS, Callee);
return llvm::InlineCost::get(InlineCost);
}