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/Pass.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Support/Debug.h" 26 #include "llvm/Support/raw_ostream.h" 27 using namespace llvm; 28 29 static cl::opt<TargetTransformInfo::TargetCostKind> CostKind( 30 "cost-kind", cl::desc("Target cost kind"), 31 cl::init(TargetTransformInfo::TCK_RecipThroughput), 32 cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput, 33 "throughput", "Reciprocal throughput"), 34 clEnumValN(TargetTransformInfo::TCK_Latency, 35 "latency", "Instruction latency"), 36 clEnumValN(TargetTransformInfo::TCK_CodeSize, 37 "code-size", "Code size"))); 38 39 #define CM_NAME "cost-model" 40 #define DEBUG_TYPE CM_NAME 41 42 namespace { 43 class CostModelAnalysis : public FunctionPass { 44 45 public: 46 static char ID; // Class identification, replacement for typeinfo 47 CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) { 48 initializeCostModelAnalysisPass( 49 *PassRegistry::getPassRegistry()); 50 } 51 52 /// Returns the expected cost of the instruction. 53 /// Returns -1 if the cost is unknown. 54 /// Note, this method does not cache the cost calculation and it 55 /// can be expensive in some cases. 56 unsigned getInstructionCost(const Instruction *I) const { 57 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput); 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; 67 /// Target information. 68 const TargetTransformInfo *TTI; 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 unsigned Cost = TTI->getInstructionCost(&Inst, CostKind); 103 if (Cost != (unsigned)-1) 104 OS << "Cost Model: Found an estimated cost of " << Cost; 105 else 106 OS << "Cost Model: Unknown cost"; 107 108 OS << " for instruction: " << Inst << "\n"; 109 } 110 } 111 } 112