| //===- InlineSimple.cpp - Code to perform simple function inlining --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements bottom-up inlining of functions into callees. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "Inliner.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Function.h" |
| #include "llvm/Type.h" |
| #include "llvm/Support/CallSite.h" |
| #include "llvm/Transforms/IPO.h" |
| using namespace llvm; |
| |
| namespace { |
| struct ArgInfo { |
| unsigned ConstantWeight; |
| unsigned AllocaWeight; |
| |
| ArgInfo(unsigned CWeight, unsigned AWeight) |
| : ConstantWeight(CWeight), AllocaWeight(AWeight) {} |
| }; |
| |
| // FunctionInfo - For each function, calculate the size of it in blocks and |
| // instructions. |
| struct FunctionInfo { |
| // HasAllocas - Keep track of whether or not a function contains an alloca |
| // instruction that is not in the entry block of the function. Inlining |
| // this call could cause us to blow out the stack, because the stack memory |
| // would never be released. |
| // |
| // FIXME: LLVM needs a way of dealloca'ing memory, which would make this |
| // irrelevant! |
| // |
| bool HasAllocas; |
| |
| // NumInsts, NumBlocks - Keep track of how large each function is, which is |
| // used to estimate the code size cost of inlining it. |
| unsigned NumInsts, NumBlocks; |
| |
| // ArgumentWeights - Each formal argument of the function is inspected to |
| // see if it is used in any contexts where making it a constant or alloca |
| // would reduce the code size. If so, we add some value to the argument |
| // entry here. |
| std::vector<ArgInfo> ArgumentWeights; |
| |
| FunctionInfo() : HasAllocas(false), NumInsts(0), NumBlocks(0) {} |
| |
| /// analyzeFunction - Fill in the current structure with information gleaned |
| /// from the specified function. |
| void analyzeFunction(Function *F); |
| }; |
| |
| class SimpleInliner : public Inliner { |
| std::map<const Function*, FunctionInfo> CachedFunctionInfo; |
| public: |
| int getInlineCost(CallSite CS); |
| }; |
| RegisterOpt<SimpleInliner> X("inline", "Function Integration/Inlining"); |
| } |
| |
| ModulePass *llvm::createFunctionInliningPass() { return new SimpleInliner(); } |
| |
| // CountCodeReductionForConstant - Figure out an approximation for how many |
| // instructions will be constant folded if the specified value is constant. |
| // |
| static unsigned 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. |
| // |
| static unsigned 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. |
| for (Instruction::op_iterator I = GEP->op_begin()+1, E = GEP->op_end(); |
| I != E; ++I) |
| if (!isa<Constant>(*I)) return 0; |
| 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 FunctionInfo::analyzeFunction(Function *F) { |
| unsigned NumInsts = 0, NumBlocks = 0; |
| |
| // Look at the size of the callee. Each basic block counts as 20 units, and |
| // each instruction counts as 10. |
| 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<DbgInfoIntrinsic>(II)) ++NumInsts; |
| |
| // If there is an alloca in the body of the function, we cannot currently |
| // inline the function without the risk of exploding the stack. |
| if (isa<AllocaInst>(II) && BB != F->begin()) { |
| HasAllocas = true; |
| this->NumBlocks = this->NumInsts = 1; |
| return; |
| } |
| } |
| |
| ++NumBlocks; |
| } |
| |
| this->NumBlocks = NumBlocks; |
| this->NumInsts = 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. |
| // |
| int SimpleInliner::getInlineCost(CallSite CS) { |
| Instruction *TheCall = CS.getInstruction(); |
| Function *Callee = CS.getCalledFunction(); |
| const Function *Caller = TheCall->getParent()->getParent(); |
| |
| // Don't inline a directly recursive call. |
| if (Caller == Callee) return 2000000000; |
| |
| // 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->hasInternalLinkage() && Callee->hasOneUse()) |
| InlineCost -= 30000; |
| |
| // 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); |
| |
| // Don't inline calls to functions with allocas that are not in the entry |
| // block of the function. |
| if (CalleeFI.HasAllocas) |
| return 2000000000; |
| |
| // 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 (AllocaInst *AI = dyn_cast<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. Here, we |
| // count each basic block as a single unit. |
| // |
| InlineCost += Caller->size()/20; |
| |
| |
| // Look at the size of the callee. Each basic block counts as 20 units, and |
| // each instruction counts as 5. |
| InlineCost += CalleeFI.NumInsts*5 + CalleeFI.NumBlocks*20; |
| return InlineCost; |
| } |
| |