1 //===- CostModel.cpp ------ Cost Model Analysis ---------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines the cost model analysis. It provides a very basic cost 10 // estimation for LLVM-IR. This analysis uses the services of the codegen 11 // to approximate the cost of any IR instruction when lowered to machine 12 // instructions. The cost results are unit-less and the cost number represents 13 // the throughput of the machine assuming that all loads hit the cache, all 14 // branches are predicted, etc. The cost numbers can be added in order to 15 // compare two or more transformation alternatives. 16 // 17 //===----------------------------------------------------------------------===// 18 19 #include "llvm/Analysis/CostModel.h" 20 #include "llvm/Analysis/Passes.h" 21 #include "llvm/Analysis/TargetTransformInfo.h" 22 #include "llvm/IR/Function.h" 23 #include "llvm/IR/PassManager.h" 24 #include "llvm/InitializePasses.h" 25 #include "llvm/Pass.h" 26 #include "llvm/Support/CommandLine.h" 27 #include "llvm/Support/raw_ostream.h" 28 #include "llvm/IR/IntrinsicInst.h" 29 using namespace llvm; 30 31 static cl::opt<TargetTransformInfo::TargetCostKind> CostKind( 32 "cost-kind", cl::desc("Target cost kind"), 33 cl::init(TargetTransformInfo::TCK_RecipThroughput), 34 cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput, 35 "throughput", "Reciprocal throughput"), 36 clEnumValN(TargetTransformInfo::TCK_Latency, 37 "latency", "Instruction latency"), 38 clEnumValN(TargetTransformInfo::TCK_CodeSize, 39 "code-size", "Code size"), 40 clEnumValN(TargetTransformInfo::TCK_SizeAndLatency, 41 "size-latency", "Code size and latency"))); 42 43 static cl::opt<bool> TypeBasedIntrinsicCost("type-based-intrinsic-cost", 44 cl::desc("Calculate intrinsics cost based only on argument types"), 45 cl::init(false)); 46 47 #define CM_NAME "cost-model" 48 #define DEBUG_TYPE CM_NAME 49 50 namespace { 51 class CostModelAnalysis : public FunctionPass { 52 53 public: 54 static char ID; // Class identification, replacement for typeinfo 55 CostModelAnalysis() : FunctionPass(ID) { 56 initializeCostModelAnalysisPass( 57 *PassRegistry::getPassRegistry()); 58 } 59 60 private: 61 void getAnalysisUsage(AnalysisUsage &AU) const override; 62 bool runOnFunction(Function &F) override; 63 void print(raw_ostream &OS, const Module*) const override; 64 65 /// The function that we analyze. 66 Function *F = nullptr; 67 /// Target information. 68 const TargetTransformInfo *TTI = nullptr; 69 }; 70 } // End of anonymous namespace 71 72 // Register this pass. 73 char CostModelAnalysis::ID = 0; 74 static const char cm_name[] = "Cost Model Analysis"; 75 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true) 76 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true) 77 78 FunctionPass *llvm::createCostModelAnalysisPass() { 79 return new CostModelAnalysis(); 80 } 81 82 void 83 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 84 AU.setPreservesAll(); 85 } 86 87 bool 88 CostModelAnalysis::runOnFunction(Function &F) { 89 this->F = &F; 90 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); 91 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr; 92 93 return false; 94 } 95 96 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const { 97 if (!F) 98 return; 99 100 for (BasicBlock &B : *F) { 101 for (Instruction &Inst : B) { 102 InstructionCost Cost; 103 auto *II = dyn_cast<IntrinsicInst>(&Inst); 104 if (II && TypeBasedIntrinsicCost) { 105 IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II, 106 InstructionCost::getInvalid(), true); 107 Cost = TTI->getIntrinsicInstrCost(ICA, CostKind); 108 } 109 else { 110 Cost = TTI->getInstructionCost(&Inst, CostKind); 111 } 112 113 if (auto CostVal = Cost.getValue()) 114 OS << "Cost Model: Found an estimated cost of " << *CostVal; 115 else 116 OS << "Cost Model: Invalid cost"; 117 118 OS << " for instruction: " << Inst << "\n"; 119 } 120 } 121 } 122 123 PreservedAnalyses CostModelPrinterPass::run(Function &F, 124 FunctionAnalysisManager &AM) { 125 auto &TTI = AM.getResult<TargetIRAnalysis>(F); 126 OS << "Printing analysis 'Cost Model Analysis' for function '" << F.getName() << "':\n"; 127 for (BasicBlock &B : F) { 128 for (Instruction &Inst : B) { 129 // TODO: Use a pass parameter instead of cl::opt CostKind to determine 130 // which cost kind to print. 131 InstructionCost Cost; 132 auto *II = dyn_cast<IntrinsicInst>(&Inst); 133 if (II && TypeBasedIntrinsicCost) { 134 IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II, 135 InstructionCost::getInvalid(), true); 136 Cost = TTI.getIntrinsicInstrCost(ICA, CostKind); 137 } 138 else { 139 Cost = TTI.getInstructionCost(&Inst, CostKind); 140 } 141 142 if (auto CostVal = Cost.getValue()) 143 OS << "Cost Model: Found an estimated cost of " << *CostVal; 144 else 145 OS << "Cost Model: Invalid cost"; 146 147 OS << " for instruction: " << Inst << "\n"; 148 } 149 } 150 return PreservedAnalyses::all(); 151 } 152