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Diffstat (limited to 'lib/Analysis/InlineCost.cpp')
| -rw-r--r-- | lib/Analysis/InlineCost.cpp | 338 |
1 files changed, 338 insertions, 0 deletions
diff --git a/lib/Analysis/InlineCost.cpp b/lib/Analysis/InlineCost.cpp new file mode 100644 index 0000000..3b0d2c9 --- /dev/null +++ b/lib/Analysis/InlineCost.cpp @@ -0,0 +1,338 @@ +//===- 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) + if (isa<BranchInst>(*UI)) + Reduction += 40; // Eliminating a conditional branch is a big win + else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI)) + // Eliminating a switch is a big win, proportional to the number of edges + // deleted. + Reduction += (SI->getNumSuccessors()-1) * 40; + else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { + // Turning an indirect call into a direct call is a BIG win + Reduction += CI->getCalledValue() == V ? 500 : 0; + } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { + // Turning an indirect call into a direct call is a BIG win + Reduction += II->getCalledValue() == V ? 500 : 0; + } else { + // Figure out if this instruction will be removed due to simple constant + // propagation. + Instruction &Inst = cast<Instruction>(**UI); + + // 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<AllocationInst>(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 += 7; + + // 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 (!isa<PointerType>(V->getType())) 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 += 10; + 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)+15; + } 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; +} + +/// analyzeBasicBlock - Fill in the current structure with information gleaned +/// from the specified block. +void CodeMetrics::analyzeBasicBlock(const BasicBlock *BB) { + ++NumBlocks; + + 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")) + NeverInline = true; + + // Calls often compile into many machine instructions. Bump up their + // cost to reflect this. + if (!isa<IntrinsicInst>(II)) + NumInsts += InlineConstants::CallPenalty; + } + + // These, too, are calls. + if (isa<MallocInst>(II) || isa<FreeInst>(II)) + NumInsts += InlineConstants::CallPenalty; + + if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) { + if (!AI->isStaticAlloca()) + this->usesDynamicAlloca = true; + } + + if (isa<ExtractElementInst>(II) || isa<VectorType>(II->getType())) + ++NumVectorInsts; + + // Noop casts, including ptr <-> int, don't count. + if (const CastInst *CI = dyn_cast<CastInst>(II)) { + if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) || + isa<PtrToIntInst>(CI)) + 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; + } + + if (isa<ReturnInst>(II)) + ++NumRets; + + ++NumInsts; + } +} + +/// 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; + + // 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. + for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) + ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I), + CountCodeReductionForAlloca(I))); +} + +// 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) { + Instruction *TheCall = CS.getInstruction(); + Function *Callee = CS.getCalledFunction(); + 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. + if (Callee->mayBeOverridden() || + Callee->hasFnAttr(Attribute::NoInline) || NeverInline.count(Callee)) + 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()) + 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.Metrics.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); + + // 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. This favors functions that take many arguments over functions + // that take few arguments. + InlineCost -= 20; + + // If this is a function being passed in, it is very likely that we will be + // able to turn an indirect function call into a direct function call. + if (isa<Function>(I)) + InlineCost -= 100; + + // 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. + // + else 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. + + // Don't inline into something too big, which would make it bigger. + // "size" here is the number of basic blocks, not instructions. + // + InlineCost += Caller->size()/15; + + // Look at the size of the callee. Each instruction counts as 5. + InlineCost += CalleeFI.Metrics.NumInsts*5; + + 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; +} |
