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/ADT/STLExtras.h" 21 #include "llvm/Analysis/Passes.h" 22 #include "llvm/Analysis/TargetTransformInfo.h" 23 #include "llvm/IR/Function.h" 24 #include "llvm/IR/PassManager.h" 25 #include "llvm/InitializePasses.h" 26 #include "llvm/Pass.h" 27 #include "llvm/Support/CommandLine.h" 28 #include "llvm/Support/Debug.h" 29 #include "llvm/Support/raw_ostream.h" 30 using namespace llvm; 31 32 static cl::opt<TargetTransformInfo::TargetCostKind> CostKind( 33 "cost-kind", cl::desc("Target cost kind"), 34 cl::init(TargetTransformInfo::TCK_RecipThroughput), 35 cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput, 36 "throughput", "Reciprocal throughput"), 37 clEnumValN(TargetTransformInfo::TCK_Latency, 38 "latency", "Instruction latency"), 39 clEnumValN(TargetTransformInfo::TCK_CodeSize, 40 "code-size", "Code size"), 41 clEnumValN(TargetTransformInfo::TCK_SizeAndLatency, 42 "size-latency", "Code size and latency"))); 43 44 45 #define CM_NAME "cost-model" 46 #define DEBUG_TYPE CM_NAME 47 48 namespace { 49 class CostModelAnalysis : public FunctionPass { 50 51 public: 52 static char ID; // Class identification, replacement for typeinfo 53 CostModelAnalysis() : FunctionPass(ID) { 54 initializeCostModelAnalysisPass( 55 *PassRegistry::getPassRegistry()); 56 } 57 58 /// Returns the expected cost of the instruction. 59 /// Returns -1 if the cost is unknown. 60 /// Note, this method does not cache the cost calculation and it 61 /// can be expensive in some cases. 62 InstructionCost getInstructionCost(const Instruction *I) const { 63 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput); 64 } 65 66 private: 67 void getAnalysisUsage(AnalysisUsage &AU) const override; 68 bool runOnFunction(Function &F) override; 69 void print(raw_ostream &OS, const Module*) const override; 70 71 /// The function that we analyze. 72 Function *F = nullptr; 73 /// Target information. 74 const TargetTransformInfo *TTI = nullptr; 75 }; 76 } // End of anonymous namespace 77 78 // Register this pass. 79 char CostModelAnalysis::ID = 0; 80 static const char cm_name[] = "Cost Model Analysis"; 81 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true) 82 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true) 83 84 FunctionPass *llvm::createCostModelAnalysisPass() { 85 return new CostModelAnalysis(); 86 } 87 88 void 89 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 90 AU.setPreservesAll(); 91 } 92 93 bool 94 CostModelAnalysis::runOnFunction(Function &F) { 95 this->F = &F; 96 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); 97 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr; 98 99 return false; 100 } 101 102 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const { 103 if (!F) 104 return; 105 106 for (BasicBlock &B : *F) { 107 for (Instruction &Inst : B) { 108 InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind); 109 if (auto CostVal = Cost.getValue()) 110 OS << "Cost Model: Found an estimated cost of " << *CostVal; 111 else 112 OS << "Cost Model: Invalid cost"; 113 114 OS << " for instruction: " << Inst << "\n"; 115 } 116 } 117 } 118 119 PreservedAnalyses CostModelPrinterPass::run(Function &F, 120 FunctionAnalysisManager &AM) { 121 auto &TTI = AM.getResult<TargetIRAnalysis>(F); 122 OS << "Cost Model for function '" << F.getName() << "'\n"; 123 for (BasicBlock &B : F) { 124 for (Instruction &Inst : B) { 125 // TODO: Use a pass parameter instead of cl::opt CostKind to determine 126 // which cost kind to print. 127 InstructionCost Cost = TTI.getInstructionCost(&Inst, CostKind); 128 if (auto CostVal = Cost.getValue()) 129 OS << "Cost Model: Found an estimated cost of " << *CostVal; 130 else 131 OS << "Cost Model: Invalid cost"; 132 133 OS << " for instruction: " << Inst << "\n"; 134 } 135 } 136 return PreservedAnalyses::all(); 137 } 138