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/ADT/STLExtras.h" 20 #include "llvm/Analysis/Passes.h" 21 #include "llvm/Analysis/TargetTransformInfo.h" 22 #include "llvm/IR/Function.h" 23 #include "llvm/InitializePasses.h" 24 #include "llvm/Pass.h" 25 #include "llvm/Support/CommandLine.h" 26 #include "llvm/Support/Debug.h" 27 #include "llvm/Support/raw_ostream.h" 28 using namespace llvm; 29 30 static cl::opt<TargetTransformInfo::TargetCostKind> CostKind( 31 "cost-kind", cl::desc("Target cost kind"), 32 cl::init(TargetTransformInfo::TCK_RecipThroughput), 33 cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput, 34 "throughput", "Reciprocal throughput"), 35 clEnumValN(TargetTransformInfo::TCK_Latency, 36 "latency", "Instruction latency"), 37 clEnumValN(TargetTransformInfo::TCK_CodeSize, 38 "code-size", "Code size"))); 39 40 #define CM_NAME "cost-model" 41 #define DEBUG_TYPE CM_NAME 42 43 namespace { 44 class CostModelAnalysis : public FunctionPass { 45 46 public: 47 static char ID; // Class identification, replacement for typeinfo 48 CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) { 49 initializeCostModelAnalysisPass( 50 *PassRegistry::getPassRegistry()); 51 } 52 53 /// Returns the expected cost of the instruction. 54 /// Returns -1 if the cost is unknown. 55 /// Note, this method does not cache the cost calculation and it 56 /// can be expensive in some cases. 57 unsigned getInstructionCost(const Instruction *I) const { 58 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput); 59 } 60 61 private: 62 void getAnalysisUsage(AnalysisUsage &AU) const override; 63 bool runOnFunction(Function &F) override; 64 void print(raw_ostream &OS, const Module*) const override; 65 66 /// The function that we analyze. 67 Function *F; 68 /// Target information. 69 const TargetTransformInfo *TTI; 70 }; 71 } // End of anonymous namespace 72 73 // Register this pass. 74 char CostModelAnalysis::ID = 0; 75 static const char cm_name[] = "Cost Model Analysis"; 76 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true) 77 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true) 78 79 FunctionPass *llvm::createCostModelAnalysisPass() { 80 return new CostModelAnalysis(); 81 } 82 83 void 84 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 85 AU.setPreservesAll(); 86 } 87 88 bool 89 CostModelAnalysis::runOnFunction(Function &F) { 90 this->F = &F; 91 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); 92 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr; 93 94 return false; 95 } 96 97 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const { 98 if (!F) 99 return; 100 101 for (BasicBlock &B : *F) { 102 for (Instruction &Inst : B) { 103 unsigned Cost = TTI->getInstructionCost(&Inst, CostKind); 104 if (Cost != (unsigned)-1) 105 OS << "Cost Model: Found an estimated cost of " << Cost; 106 else 107 OS << "Cost Model: Unknown cost"; 108 109 OS << " for instruction: " << Inst << "\n"; 110 } 111 } 112 } 113