Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 1 | //===- InlineCoast.cpp - Cost analysis for inliner ------------------------===// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
Chris Lattner | 4ee451d | 2007-12-29 20:36:04 +0000 | [diff] [blame] | 5 | // This file is distributed under the University of Illinois Open Source |
| 6 | // License. See LICENSE.TXT for details. |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | // |
| 10 | // This file implements inline cost analysis. |
| 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
| 14 | |
| 15 | #include "llvm/Transforms/Utils/InlineCost.h" |
| 16 | #include "llvm/Support/CallSite.h" |
| 17 | #include "llvm/CallingConv.h" |
| 18 | #include "llvm/IntrinsicInst.h" |
| 19 | |
| 20 | using namespace llvm; |
| 21 | |
| 22 | // CountCodeReductionForConstant - Figure out an approximation for how many |
| 23 | // instructions will be constant folded if the specified value is constant. |
| 24 | // |
| 25 | unsigned InlineCostAnalyzer::FunctionInfo:: |
| 26 | CountCodeReductionForConstant(Value *V) { |
| 27 | unsigned Reduction = 0; |
| 28 | for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI) |
| 29 | if (isa<BranchInst>(*UI)) |
| 30 | Reduction += 40; // Eliminating a conditional branch is a big win |
| 31 | else if (SwitchInst *SI = dyn_cast<SwitchInst>(*UI)) |
| 32 | // Eliminating a switch is a big win, proportional to the number of edges |
| 33 | // deleted. |
| 34 | Reduction += (SI->getNumSuccessors()-1) * 40; |
| 35 | else if (CallInst *CI = dyn_cast<CallInst>(*UI)) { |
| 36 | // Turning an indirect call into a direct call is a BIG win |
| 37 | Reduction += CI->getCalledValue() == V ? 500 : 0; |
| 38 | } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) { |
| 39 | // Turning an indirect call into a direct call is a BIG win |
| 40 | Reduction += II->getCalledValue() == V ? 500 : 0; |
| 41 | } else { |
| 42 | // Figure out if this instruction will be removed due to simple constant |
| 43 | // propagation. |
| 44 | Instruction &Inst = cast<Instruction>(**UI); |
| 45 | bool AllOperandsConstant = true; |
| 46 | for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i) |
| 47 | if (!isa<Constant>(Inst.getOperand(i)) && Inst.getOperand(i) != V) { |
| 48 | AllOperandsConstant = false; |
| 49 | break; |
| 50 | } |
| 51 | |
| 52 | if (AllOperandsConstant) { |
| 53 | // We will get to remove this instruction... |
| 54 | Reduction += 7; |
| 55 | |
| 56 | // And any other instructions that use it which become constants |
| 57 | // themselves. |
| 58 | Reduction += CountCodeReductionForConstant(&Inst); |
| 59 | } |
| 60 | } |
| 61 | |
| 62 | return Reduction; |
| 63 | } |
| 64 | |
| 65 | // CountCodeReductionForAlloca - Figure out an approximation of how much smaller |
| 66 | // the function will be if it is inlined into a context where an argument |
| 67 | // becomes an alloca. |
| 68 | // |
| 69 | unsigned InlineCostAnalyzer::FunctionInfo:: |
| 70 | CountCodeReductionForAlloca(Value *V) { |
| 71 | if (!isa<PointerType>(V->getType())) return 0; // Not a pointer |
| 72 | unsigned Reduction = 0; |
| 73 | for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ |
| 74 | Instruction *I = cast<Instruction>(*UI); |
| 75 | if (isa<LoadInst>(I) || isa<StoreInst>(I)) |
| 76 | Reduction += 10; |
| 77 | else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) { |
| 78 | // If the GEP has variable indices, we won't be able to do much with it. |
| 79 | for (Instruction::op_iterator I = GEP->op_begin()+1, E = GEP->op_end(); |
| 80 | I != E; ++I) |
| 81 | if (!isa<Constant>(*I)) return 0; |
| 82 | Reduction += CountCodeReductionForAlloca(GEP)+15; |
| 83 | } else { |
| 84 | // If there is some other strange instruction, we're not going to be able |
| 85 | // to do much if we inline this. |
| 86 | return 0; |
| 87 | } |
| 88 | } |
| 89 | |
| 90 | return Reduction; |
| 91 | } |
| 92 | |
| 93 | /// analyzeFunction - Fill in the current structure with information gleaned |
| 94 | /// from the specified function. |
| 95 | void InlineCostAnalyzer::FunctionInfo::analyzeFunction(Function *F) { |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 96 | unsigned NumInsts = 0, NumBlocks = 0, NumVectorInsts = 0; |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 97 | |
| 98 | // Look at the size of the callee. Each basic block counts as 20 units, and |
Devang Patel | 161660e | 2007-09-17 20:07:40 +0000 | [diff] [blame] | 99 | // each instruction counts as 5. |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 100 | for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { |
| 101 | for (BasicBlock::const_iterator II = BB->begin(), E = BB->end(); |
| 102 | II != E; ++II) { |
| 103 | if (isa<DbgInfoIntrinsic>(II)) continue; // Debug intrinsics don't count. |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 104 | if (isa<PHINode>(II)) continue; // PHI nodes don't count. |
| 105 | |
| 106 | if (isa<InsertElementInst>(II) || isa<ExtractElementInst>(II) || |
| 107 | isa<ShuffleVectorInst>(II) || isa<VectorType>(II->getType())) |
| 108 | ++NumVectorInsts; |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 109 | |
| 110 | // Noop casts, including ptr <-> int, don't count. |
| 111 | if (const CastInst *CI = dyn_cast<CastInst>(II)) { |
| 112 | if (CI->isLosslessCast() || isa<IntToPtrInst>(CI) || |
| 113 | isa<PtrToIntInst>(CI)) |
| 114 | continue; |
| 115 | } else if (const GetElementPtrInst *GEPI = |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 116 | dyn_cast<GetElementPtrInst>(II)) { |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 117 | // If a GEP has all constant indices, it will probably be folded with |
| 118 | // a load/store. |
| 119 | bool AllConstant = true; |
| 120 | for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i) |
| 121 | if (!isa<ConstantInt>(GEPI->getOperand(i))) { |
| 122 | AllConstant = false; |
| 123 | break; |
| 124 | } |
| 125 | if (AllConstant) continue; |
| 126 | } |
| 127 | |
| 128 | ++NumInsts; |
| 129 | } |
| 130 | |
| 131 | ++NumBlocks; |
| 132 | } |
| 133 | |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 134 | this->NumBlocks = NumBlocks; |
| 135 | this->NumInsts = NumInsts; |
| 136 | this->NumVectorInsts = NumVectorInsts; |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 137 | |
| 138 | // Check out all of the arguments to the function, figuring out how much |
| 139 | // code can be eliminated if one of the arguments is a constant. |
| 140 | for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I) |
| 141 | ArgumentWeights.push_back(ArgInfo(CountCodeReductionForConstant(I), |
| 142 | CountCodeReductionForAlloca(I))); |
| 143 | } |
| 144 | |
| 145 | |
| 146 | |
| 147 | // getInlineCost - The heuristic used to determine if we should inline the |
| 148 | // function call or not. |
| 149 | // |
Evan Cheng | 71d8374 | 2008-03-20 00:20:23 +0000 | [diff] [blame] | 150 | int InlineCostAnalyzer::getInlineCost(CallSite CS, |
| 151 | SmallPtrSet<const Function *, 16> &NeverInline) { |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 152 | Instruction *TheCall = CS.getInstruction(); |
| 153 | Function *Callee = CS.getCalledFunction(); |
| 154 | const Function *Caller = TheCall->getParent()->getParent(); |
| 155 | |
| 156 | // Don't inline a directly recursive call. |
| 157 | if (Caller == Callee || |
| 158 | // Don't inline functions which can be redefined at link-time to mean |
| 159 | // something else. link-once linkage is ok though. |
| 160 | Callee->hasWeakLinkage() || |
| 161 | |
| 162 | // Don't inline functions marked noinline. |
| 163 | NeverInline.count(Callee)) |
| 164 | return 2000000000; |
| 165 | |
| 166 | // InlineCost - This value measures how good of an inline candidate this call |
| 167 | // site is to inline. A lower inline cost make is more likely for the call to |
| 168 | // be inlined. This value may go negative. |
| 169 | // |
| 170 | int InlineCost = 0; |
| 171 | |
| 172 | // If there is only one call of the function, and it has internal linkage, |
| 173 | // make it almost guaranteed to be inlined. |
| 174 | // |
| 175 | if (Callee->hasInternalLinkage() && Callee->hasOneUse()) |
| 176 | InlineCost -= 30000; |
| 177 | |
| 178 | // If this function uses the coldcc calling convention, prefer not to inline |
| 179 | // it. |
| 180 | if (Callee->getCallingConv() == CallingConv::Cold) |
| 181 | InlineCost += 2000; |
| 182 | |
| 183 | // If the instruction after the call, or if the normal destination of the |
| 184 | // invoke is an unreachable instruction, the function is noreturn. As such, |
| 185 | // there is little point in inlining this. |
| 186 | if (InvokeInst *II = dyn_cast<InvokeInst>(TheCall)) { |
| 187 | if (isa<UnreachableInst>(II->getNormalDest()->begin())) |
| 188 | InlineCost += 10000; |
| 189 | } else if (isa<UnreachableInst>(++BasicBlock::iterator(TheCall))) |
| 190 | InlineCost += 10000; |
| 191 | |
| 192 | // Get information about the callee... |
| 193 | FunctionInfo &CalleeFI = CachedFunctionInfo[Callee]; |
| 194 | |
| 195 | // If we haven't calculated this information yet, do so now. |
| 196 | if (CalleeFI.NumBlocks == 0) |
| 197 | CalleeFI.analyzeFunction(Callee); |
| 198 | |
| 199 | // Add to the inline quality for properties that make the call valuable to |
| 200 | // inline. This includes factors that indicate that the result of inlining |
| 201 | // the function will be optimizable. Currently this just looks at arguments |
| 202 | // passed into the function. |
| 203 | // |
| 204 | unsigned ArgNo = 0; |
| 205 | for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); |
| 206 | I != E; ++I, ++ArgNo) { |
| 207 | // Each argument passed in has a cost at both the caller and the callee |
| 208 | // sides. This favors functions that take many arguments over functions |
| 209 | // that take few arguments. |
| 210 | InlineCost -= 20; |
| 211 | |
| 212 | // If this is a function being passed in, it is very likely that we will be |
| 213 | // able to turn an indirect function call into a direct function call. |
| 214 | if (isa<Function>(I)) |
| 215 | InlineCost -= 100; |
| 216 | |
| 217 | // If an alloca is passed in, inlining this function is likely to allow |
| 218 | // significant future optimization possibilities (like scalar promotion, and |
| 219 | // scalarization), so encourage the inlining of the function. |
| 220 | // |
| 221 | else if (isa<AllocaInst>(I)) { |
| 222 | if (ArgNo < CalleeFI.ArgumentWeights.size()) |
| 223 | InlineCost -= CalleeFI.ArgumentWeights[ArgNo].AllocaWeight; |
| 224 | |
| 225 | // If this is a constant being passed into the function, use the argument |
| 226 | // weights calculated for the callee to determine how much will be folded |
| 227 | // away with this information. |
| 228 | } else if (isa<Constant>(I)) { |
| 229 | if (ArgNo < CalleeFI.ArgumentWeights.size()) |
| 230 | InlineCost -= CalleeFI.ArgumentWeights[ArgNo].ConstantWeight; |
| 231 | } |
| 232 | } |
| 233 | |
| 234 | // Now that we have considered all of the factors that make the call site more |
| 235 | // likely to be inlined, look at factors that make us not want to inline it. |
| 236 | |
Evan Cheng | 7c3becd | 2008-04-01 23:59:29 +0000 | [diff] [blame] | 237 | // Don't inline into something too big, which would make it bigger. |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 238 | // |
| 239 | InlineCost += Caller->size()/20; |
| 240 | |
Evan Cheng | 7c3becd | 2008-04-01 23:59:29 +0000 | [diff] [blame] | 241 | // Look at the size of the callee. Each instruction counts as 5. |
| 242 | InlineCost += CalleeFI.NumInsts*5; |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 243 | |
Devang Patel | 6899b31 | 2007-07-25 18:00:25 +0000 | [diff] [blame] | 244 | return InlineCost; |
| 245 | } |
| 246 | |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 247 | // getInlineFudgeFactor - Return a > 1.0 factor if the inliner should use a |
| 248 | // higher threshold to determine if the function call should be inlined. |
| 249 | float InlineCostAnalyzer::getInlineFudgeFactor(CallSite CS) { |
| 250 | Function *Callee = CS.getCalledFunction(); |
| 251 | |
| 252 | // Get information about the callee... |
| 253 | FunctionInfo &CalleeFI = CachedFunctionInfo[Callee]; |
| 254 | |
| 255 | // If we haven't calculated this information yet, do so now. |
| 256 | if (CalleeFI.NumBlocks == 0) |
| 257 | CalleeFI.analyzeFunction(Callee); |
| 258 | |
Evan Cheng | 7c3becd | 2008-04-01 23:59:29 +0000 | [diff] [blame] | 259 | float Factor = 1.0f; |
| 260 | // Single BB functions are often written to be inlined. |
| 261 | if (CalleeFI.NumBlocks == 1) |
| 262 | Factor += 0.5f; |
| 263 | |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 264 | // Be more aggressive if the function contains a good chunk (if it mades up |
| 265 | // at least 10% of the instructions) of vector instructions. |
Evan Cheng | 7c3becd | 2008-04-01 23:59:29 +0000 | [diff] [blame] | 266 | if (CalleeFI.NumVectorInsts > CalleeFI.NumInsts/2) |
| 267 | Factor += 2.0f; |
| 268 | else if (CalleeFI.NumVectorInsts > CalleeFI.NumInsts/10) |
| 269 | Factor += 1.5f; |
| 270 | return Factor; |
Evan Cheng | 8d84d5b | 2008-03-24 06:37:48 +0000 | [diff] [blame] | 271 | } |