//===- 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/Transforms/Utils/InlineCost.h" #include "llvm/Support/CallSite.h" #include "llvm/CallingConv.h" #include "llvm/IntrinsicInst.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); 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; } /// analyzeFunction - Fill in the current structure with information gleaned /// from the specified function. void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) { unsigned NumInsts = 0, NumBlocks = 0, NumVectorInsts = 0; // Look at the size of the callee. Each basic block counts as 20 units, and // each instruction counts as 5. for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 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->isName("setjmp") || F->isName("_setjmp"))) { NeverInline = true; return; } // Calls often compile into many machine instructions. Bump up their // cost to reflect this. if (!isa<IntrinsicInst>(II)) NumInsts += 5; } 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; } ++NumInsts; } ++NumBlocks; } this->NumBlocks = NumBlocks; this->NumInsts = NumInsts; this->NumVectorInsts = NumVectorInsts; // 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. if (Callee->mayBeOverridden() || // Don't inline functions marked noinline. 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 -= 15000; // If this function uses the coldcc calling convention, prefer not to inline // it. if (Callee->getCallingConv() == CallingConv::Cold) InlineCost += 2000; // 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 += 10000; } else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall))) InlineCost += 10000; // Get information about the callee... FunctionInfo &CalleeFI = CachedFunctionInfo[Callee]; // If we haven't calculated this information yet, do so now. if (CalleeFI.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.usesDynamicAlloca) { // Get infomation about the caller... FunctionInfo &CallerFI = CachedFunctionInfo[Caller]; // If we haven't calculated this information yet, do so now. if (CallerFI.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.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. // InlineCost += Caller->size()/15; // Look at the size of the callee. Each instruction counts as 5. InlineCost += CalleeFI.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.NumBlocks == 0) CalleeFI.analyzeFunction(Callee); float Factor = 1.0f; // Single BB functions are often written to be inlined. if (CalleeFI.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.NumVectorInsts > CalleeFI.NumInsts/2) Factor += 2.0f; else if (CalleeFI.NumVectorInsts > CalleeFI.NumInsts/10) Factor += 1.5f; return Factor; }