| //===- CostModel.cpp ------ Cost Model Analysis ---------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines the cost model analysis. It provides a very basic cost |
| // estimation for LLVM-IR. This analysis uses the services of the codegen |
| // to approximate the cost of any IR instruction when lowered to machine |
| // instructions. The cost results are unit-less and the cost number represents |
| // the throughput of the machine assuming that all loads hit the cache, all |
| // branches are predicted, etc. The cost numbers can be added in order to |
| // compare two or more transformation alternatives. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/Analysis/Passes.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| using namespace llvm; |
| |
| static cl::opt<TargetTransformInfo::TargetCostKind> CostKind( |
| "cost-kind", cl::desc("Target cost kind"), |
| cl::init(TargetTransformInfo::TCK_RecipThroughput), |
| cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput, |
| "throughput", "Reciprocal throughput"), |
| clEnumValN(TargetTransformInfo::TCK_Latency, |
| "latency", "Instruction latency"), |
| clEnumValN(TargetTransformInfo::TCK_CodeSize, |
| "code-size", "Code size"), |
| clEnumValN(TargetTransformInfo::TCK_SizeAndLatency, |
| "size-latency", "Code size and latency"))); |
| |
| |
| #define CM_NAME "cost-model" |
| #define DEBUG_TYPE CM_NAME |
| |
| namespace { |
| class CostModelAnalysis : public FunctionPass { |
| |
| public: |
| static char ID; // Class identification, replacement for typeinfo |
| CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) { |
| initializeCostModelAnalysisPass( |
| *PassRegistry::getPassRegistry()); |
| } |
| |
| /// Returns the expected cost of the instruction. |
| /// Returns -1 if the cost is unknown. |
| /// Note, this method does not cache the cost calculation and it |
| /// can be expensive in some cases. |
| InstructionCost getInstructionCost(const Instruction *I) const { |
| return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput); |
| } |
| |
| private: |
| void getAnalysisUsage(AnalysisUsage &AU) const override; |
| bool runOnFunction(Function &F) override; |
| void print(raw_ostream &OS, const Module*) const override; |
| |
| /// The function that we analyze. |
| Function *F; |
| /// Target information. |
| const TargetTransformInfo *TTI; |
| }; |
| } // End of anonymous namespace |
| |
| // Register this pass. |
| char CostModelAnalysis::ID = 0; |
| static const char cm_name[] = "Cost Model Analysis"; |
| INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true) |
| INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true) |
| |
| FunctionPass *llvm::createCostModelAnalysisPass() { |
| return new CostModelAnalysis(); |
| } |
| |
| void |
| CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesAll(); |
| } |
| |
| bool |
| CostModelAnalysis::runOnFunction(Function &F) { |
| this->F = &F; |
| auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>(); |
| TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr; |
| |
| return false; |
| } |
| |
| void CostModelAnalysis::print(raw_ostream &OS, const Module*) const { |
| if (!F) |
| return; |
| |
| for (BasicBlock &B : *F) { |
| for (Instruction &Inst : B) { |
| InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind); |
| if (auto CostVal = Cost.getValue()) |
| OS << "Cost Model: Found an estimated cost of " << *CostVal; |
| else |
| OS << "Cost Model: Invalid cost"; |
| |
| OS << " for instruction: " << Inst << "\n"; |
| } |
| } |
| } |