| //===- 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); |
| |
| // 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; |
| } |
| |
| /// 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->getName() == "setjmp" || F->getName() == "_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; |
| } |
