//===- 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(*UI) || isa(*UI)) { // We will be able to eliminate all but one of the successors. const TerminatorInst &TI = cast(**UI); const unsigned NumSucc = TI.getNumSuccessors(); unsigned Instrs = 0; for (unsigned I = 0; I != NumSucc; ++I) Instrs += TI.getSuccessor(I)->size(); // 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(*UI)) { // 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(*UI)) { // 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(**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(Inst)) continue; bool AllOperandsConstant = true; for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i) if (!isa(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(*UI); if (isa(I) || isa(I)) Reduction += InlineConstants::InstrCost; else if (GetElementPtrInst *GEP = dyn_cast(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(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? static bool 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 == "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; for (BasicBlock::const_iterator II = BB->begin(), E = BB->end(); II != E; ++II) { if (isa(II)) continue; // PHI nodes don't count. // Special handling for calls. if (isa(II) || isa(II)) { if (isa(II)) continue; // Debug intrinsics don't count as size. CallSite CS = CallSite::get(const_cast(&*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; if (!isa(II) && !callIsSmall(CS.getCalledFunction())) { // Each argument to a call takes on average one instruction to set up. NumInsts += CS.arg_size(); ++NumCalls; } } if (const AllocaInst *AI = dyn_cast(II)) { if (!AI->isStaticAlloca()) this->usesDynamicAlloca = true; } if (isa(II) || II->getType()->isVectorTy()) ++NumVectorInsts; if (const CastInst *CI = dyn_cast(II)) { // Noop casts, including ptr <-> int, don't count. if (CI->isLosslessCast() || isa(CI) || isa(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(CI->getOperand(0))) continue; } else if (const GetElementPtrInst *GEPI = dyn_cast(II)){ // If a GEP has all constant indices, it will probably be folded with // a load/store. if (GEPI->hasAllConstantIndices()) continue; } ++NumInsts; } if (isa(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(BB->getTerminator())) NeverInline = true; } /// 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 (Metrics.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))); } // getInlineCost - The heuristic used to determine if we should inline the // function call or not. // InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS, SmallPtrSet &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(TheCall)) { if (isa(II->getNormalDest()->begin())) InlineCost += InlineConstants::NoreturnPenalty; } else if (isa(++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. 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(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(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) { FunctionInfo &CallerFI = CachedFunctionInfo[Caller]; // For small functions we prefer to recalculate the cost for better accuracy. if (CallerFI.Metrics.NumBlocks < 10 || CallerFI.Metrics.NumInsts < 1000) { resetCachedCostInfo(Caller); return; } // For large functions, we can save a lot of computation time by skipping // recalculations. if (CallerFI.Metrics.NumCalls > 0) --CallerFI.Metrics.NumCalls; if (Callee) { FunctionInfo &CalleeFI = CachedFunctionInfo[Callee]; if (!CalleeFI.Metrics.NumBlocks) { resetCachedCostInfo(Caller); return; } CallerFI.Metrics.NeverInline |= CalleeFI.Metrics.NeverInline; CallerFI.Metrics.usesDynamicAlloca |= CalleeFI.Metrics.usesDynamicAlloca; CallerFI.Metrics.NumInsts += CalleeFI.Metrics.NumInsts; CallerFI.Metrics.NumBlocks += CalleeFI.Metrics.NumBlocks; CallerFI.Metrics.NumCalls += CalleeFI.Metrics.NumCalls; CallerFI.Metrics.NumVectorInsts += CalleeFI.Metrics.NumVectorInsts; CallerFI.Metrics.NumRets += CalleeFI.Metrics.NumRets; // analyzeBasicBlock counts each function argument as an inst. if (CallerFI.Metrics.NumInsts >= Callee->arg_size()) CallerFI.Metrics.NumInsts -= Callee->arg_size(); else CallerFI.Metrics.NumInsts = 0; } // We are not updating the argumentweights. We have already determined that // Caller is a fairly large function, so we accept the loss of precision. }