InlineSimple.cpp revision 9133fe28954d498fc4de13064c7d65bd811de02c
1//===- InlineSimple.cpp - Code to perform simple function inlining --------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements bottom-up inlining of functions into callees. 11// 12//===----------------------------------------------------------------------===// 13 14#include "Inliner.h" 15#include "llvm/CallingConv.h" 16#include "llvm/Instructions.h" 17#include "llvm/IntrinsicInst.h" 18#include "llvm/Function.h" 19#include "llvm/Type.h" 20#include "llvm/Support/CallSite.h" 21#include "llvm/Support/Compiler.h" 22#include "llvm/Transforms/IPO.h" 23using namespace llvm; 24 25namespace { 26 struct VISIBILITY_HIDDEN ArgInfo { 27 unsigned ConstantWeight; 28 unsigned AllocaWeight; 29 30 ArgInfo(unsigned CWeight, unsigned AWeight) 31 : ConstantWeight(CWeight), AllocaWeight(AWeight) {} 32 }; 33 34 // FunctionInfo - For each function, calculate the size of it in blocks and 35 // instructions. 36 struct VISIBILITY_HIDDEN FunctionInfo { 37 // NumInsts, NumBlocks - Keep track of how large each function is, which is 38 // used to estimate the code size cost of inlining it. 39 unsigned NumInsts, NumBlocks; 40 41 // ArgumentWeights - Each formal argument of the function is inspected to 42 // see if it is used in any contexts where making it a constant or alloca 43 // would reduce the code size. If so, we add some value to the argument 44 // entry here. 45 std::vector<ArgInfo> ArgumentWeights; 46 47 FunctionInfo() : NumInsts(0), NumBlocks(0) {} 48 49 /// analyzeFunction - Fill in the current structure with information gleaned 50 /// from the specified function. 51 void analyzeFunction(Function *F); 52 }; 53 54 class VISIBILITY_HIDDEN SimpleInliner : public Inliner { 55 std::map<const Function*, FunctionInfo> CachedFunctionInfo; 56 public: 57 int getInlineCost(CallSite CS); 58 }; 59 RegisterPass<SimpleInliner> X("inline", "Function Integration/Inlining"); 60} 61 62Pass *llvm::createFunctionInliningPass() { return new SimpleInliner(); } 63 64// CountCodeReductionForConstant - Figure out an approximation for how many 65// instructions will be constant folded if the specified value is constant. 66// 67static unsigned CountCodeReductionForConstant(Value *V) { 68 unsigned Reduction = 0; 69 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) 70 if (isa<BranchInst>(*UI)) 71 Reduction += 40; // Eliminating a conditional branch is a big win 72 else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI)) 73 // Eliminating a switch is a big win, proportional to the number of edges 74 // deleted. 75 Reduction += (SI->getNumSuccessors()-1) * 40; 76 else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { 77 // Turning an indirect call into a direct call is a BIG win 78 Reduction += CI->getCalledValue() == V ? 500 : 0; 79 } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { 80 // Turning an indirect call into a direct call is a BIG win 81 Reduction += II->getCalledValue() == V ? 500 : 0; 82 } else { 83 // Figure out if this instruction will be removed due to simple constant 84 // propagation. 85 Instruction &Inst = cast<Instruction>(**UI); 86 bool AllOperandsConstant = true; 87 for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i) 88 if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) { 89 AllOperandsConstant = false; 90 break; 91 } 92 93 if (AllOperandsConstant) { 94 // We will get to remove this instruction... 95 Reduction += 7; 96 97 // And any other instructions that use it which become constants 98 // themselves. 99 Reduction += CountCodeReductionForConstant(&Inst); 100 } 101 } 102 103 return Reduction; 104} 105 106// CountCodeReductionForAlloca - Figure out an approximation of how much smaller 107// the function will be if it is inlined into a context where an argument 108// becomes an alloca. 109// 110static unsigned CountCodeReductionForAlloca(Value *V) { 111 if (!isa<PointerType>(V->getType())) return 0; // Not a pointer 112 unsigned Reduction = 0; 113 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ 114 Instruction *I = cast<Instruction>(*UI); 115 if (isa<LoadInst>(I) || isa<StoreInst>(I)) 116 Reduction += 10; 117 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { 118 // If the GEP has variable indices, we won't be able to do much with it. 119 for (Instruction::op_iterator I = GEP->op_begin()+1, E = GEP->op_end(); 120 I != E; ++I) 121 if (!isa<Constant>(*I)) return 0; 122 Reduction += CountCodeReductionForAlloca(GEP)+15; 123 } else { 124 // If there is some other strange instruction, we're not going to be able 125 // to do much if we inline this. 126 return 0; 127 } 128 } 129 130 return Reduction; 131} 132 133/// analyzeFunction - Fill in the current structure with information gleaned 134/// from the specified function. 135void FunctionInfo::analyzeFunction(Function *F) { 136 unsigned NumInsts = 0, NumBlocks = 0; 137 138 // Look at the size of the callee. Each basic block counts as 20 units, and 139 // each instruction counts as 10. 140 for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 141 for (BasicBlock::const_iterator II = BB->begin(), E = BB->end(); 142 II != E; ++II) { 143 if (isa<DbgInfoIntrinsic>(II)) continue; // Debug intrinsics don't count. 144 145 // Noop casts, including ptr <-> int, don't count. 146 if (const CastInst *CI = dyn_cast<CastInst>(II)) { 147 if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) || 148 isa<PtrToIntInst>(CI)) 149 continue; 150 } else if (const GetElementPtrInst *GEPI = 151 dyn_cast<GetElementPtrInst>(II)) { 152 // If a GEP has all constant indices, it will probably be folded with 153 // a load/store. 154 bool AllConstant = true; 155 for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) 156 if (!isa<ConstantInt>(GEPI->getOperand(i))) { 157 AllConstant = false; 158 break; 159 } 160 if (AllConstant) continue; 161 } 162 163 ++NumInsts; 164 } 165 166 ++NumBlocks; 167 } 168 169 this->NumBlocks = NumBlocks; 170 this->NumInsts = NumInsts; 171 172 // Check out all of the arguments to the function, figuring out how much 173 // code can be eliminated if one of the arguments is a constant. 174 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) 175 ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I), 176 CountCodeReductionForAlloca(I))); 177} 178 179 180// getInlineCost - The heuristic used to determine if we should inline the 181// function call or not. 182// 183int SimpleInliner::getInlineCost(CallSite CS) { 184 Instruction *TheCall = CS.getInstruction(); 185 Function *Callee = CS.getCalledFunction(); 186 const Function *Caller = TheCall->getParent()->getParent(); 187 188 // Don't inline a directly recursive call. 189 if (Caller == Callee) return 2000000000; 190 191 // InlineCost - This value measures how good of an inline candidate this call 192 // site is to inline. A lower inline cost make is more likely for the call to 193 // be inlined. This value may go negative. 194 // 195 int InlineCost = 0; 196 197 // If there is only one call of the function, and it has internal linkage, 198 // make it almost guaranteed to be inlined. 199 // 200 if (Callee->hasInternalLinkage() && Callee->hasOneUse()) 201 InlineCost -= 30000; 202 203 // If this function uses the coldcc calling convention, prefer not to inline 204 // it. 205 if (Callee->getCallingConv() == CallingConv::Cold) 206 InlineCost += 2000; 207 208 // If the instruction after the call, or if the normal destination of the 209 // invoke is an unreachable instruction, the function is noreturn. As such, 210 // there is little point in inlining this. 211 if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) { 212 if (isa<UnreachableInst>(II->getNormalDest()->begin())) 213 InlineCost += 10000; 214 } else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall))) 215 InlineCost += 10000; 216 217 // Get information about the callee... 218 FunctionInfo &CalleeFI = CachedFunctionInfo[Callee]; 219 220 // If we haven't calculated this information yet, do so now. 221 if (CalleeFI.NumBlocks == 0) 222 CalleeFI.analyzeFunction(Callee); 223 224 // Add to the inline quality for properties that make the call valuable to 225 // inline. This includes factors that indicate that the result of inlining 226 // the function will be optimizable. Currently this just looks at arguments 227 // passed into the function. 228 // 229 unsigned ArgNo = 0; 230 for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); 231 I != E; ++I, ++ArgNo) { 232 // Each argument passed in has a cost at both the caller and the callee 233 // sides. This favors functions that take many arguments over functions 234 // that take few arguments. 235 InlineCost -= 20; 236 237 // If this is a function being passed in, it is very likely that we will be 238 // able to turn an indirect function call into a direct function call. 239 if (isa<Function>(I)) 240 InlineCost -= 100; 241 242 // If an alloca is passed in, inlining this function is likely to allow 243 // significant future optimization possibilities (like scalar promotion, and 244 // scalarization), so encourage the inlining of the function. 245 // 246 else if (isa<AllocaInst>(I)) { 247 if (ArgNo < CalleeFI.ArgumentWeights.size()) 248 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].AllocaWeight; 249 250 // If this is a constant being passed into the function, use the argument 251 // weights calculated for the callee to determine how much will be folded 252 // away with this information. 253 } else if (isa<Constant>(I)) { 254 if (ArgNo < CalleeFI.ArgumentWeights.size()) 255 InlineCost -= CalleeFI.ArgumentWeights[ArgNo].ConstantWeight; 256 } 257 } 258 259 // Now that we have considered all of the factors that make the call site more 260 // likely to be inlined, look at factors that make us not want to inline it. 261 262 // Don't inline into something too big, which would make it bigger. Here, we 263 // count each basic block as a single unit. 264 // 265 InlineCost += Caller->size()/20; 266 267 268 // Look at the size of the callee. Each basic block counts as 20 units, and 269 // each instruction counts as 5. 270 InlineCost += CalleeFI.NumInsts*5 + CalleeFI.NumBlocks*20; 271 return InlineCost; 272} 273 274