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 /// Returns the expected cost of the instruction. 61 /// Returns -1 if the cost is unknown. 62 /// Note, this method does not cache the cost calculation and it 63 /// can be expensive in some cases. 64 InstructionCost getInstructionCost(const Instruction *I) const { 65 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput); 66 } 67 68 private: 69 void getAnalysisUsage(AnalysisUsage &AU) const override; 70 bool runOnFunction(Function &F) override; 71 void print(raw_ostream &OS, const Module*) const override; 72 73 /// The function that we analyze. 74 Function *F = nullptr; 75 /// Target information. 76 const TargetTransformInfo *TTI = nullptr; 77 }; 78 } // End of anonymous namespace 79 80 // Register this pass. 81 char CostModelAnalysis::ID = 0; 82 static const char cm_name[] = "Cost Model Analysis"; 83 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true) 84 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true) 85 86 FunctionPass *llvm::createCostModelAnalysisPass() { 87 return new CostModelAnalysis(); 88 } 89 90 void 91 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { 92 AU.setPreservesAll(); 93 } 94 95 bool 96 CostModelAnalysis::runOnFunction(Function &F) { 97 this->F = &F; 98 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); 99 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr; 100 101 return false; 102 } 103 104 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const { 105 if (!F) 106 return; 107 108 for (BasicBlock &B : *F) { 109 for (Instruction &Inst : B) { 110 InstructionCost Cost; 111 if (TypeBasedIntrinsicCost && isa<IntrinsicInst>(&Inst)) { 112 auto *II = dyn_cast<IntrinsicInst>(&Inst); 113 IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II, 114 InstructionCost::getInvalid(), true); 115 Cost = TTI->getIntrinsicInstrCost(ICA, CostKind); 116 } 117 else { 118 Cost = TTI->getInstructionCost(&Inst, CostKind); 119 } 120 if (auto CostVal = Cost.getValue()) 121 OS << "Cost Model: Found an estimated cost of " << *CostVal; 122 else 123 OS << "Cost Model: Invalid cost"; 124 125 OS << " for instruction: " << Inst << "\n"; 126 } 127 } 128 } 129 130 PreservedAnalyses CostModelPrinterPass::run(Function &F, 131 FunctionAnalysisManager &AM) { 132 auto &TTI = AM.getResult<TargetIRAnalysis>(F); 133 OS << "Printing analysis 'Cost Model Analysis' for function '" << F.getName() << "':\n"; 134 for (BasicBlock &B : F) { 135 for (Instruction &Inst : B) { 136 // TODO: Use a pass parameter instead of cl::opt CostKind to determine 137 // which cost kind to print. 138 InstructionCost Cost; 139 if (TypeBasedIntrinsicCost && isa<IntrinsicInst>(&Inst)) { 140 auto *II = dyn_cast<IntrinsicInst>(&Inst); 141 IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II, 142 InstructionCost::getInvalid(), true); 143 Cost = TTI.getIntrinsicInstrCost(ICA, CostKind); 144 } 145 else { 146 Cost = TTI.getInstructionCost(&Inst, CostKind); 147 } 148 if (auto CostVal = Cost.getValue()) 149 OS << "Cost Model: Found an estimated cost of " << *CostVal; 150 else 151 OS << "Cost Model: Invalid cost"; 152 153 OS << " for instruction: " << Inst << "\n"; 154 } 155 } 156 return PreservedAnalyses::all(); 157 } 158