llvm/lib/Analysis/CostModel.cpp

   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   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 = nullptr;
  67     /// Target information.
  68     const TargetTransformInfo *TTI = nullptr;
  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       InstructionCost Cost;
 103       auto *II = dyn_cast<IntrinsicInst>(&Inst);
 104       if (II && TypeBasedIntrinsicCost) {
 105         IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II,
 106                                     InstructionCost::getInvalid(), true);
 107         Cost = TTI->getIntrinsicInstrCost(ICA, CostKind);
 108       }
 109       else {
 110         Cost = TTI->getInstructionCost(&Inst, CostKind);
 111       }
 112
 113       if (auto CostVal = Cost.getValue())
 114         OS << "Cost Model: Found an estimated cost of " << *CostVal;
 115       else
 116         OS << "Cost Model: Invalid cost";
 117
 118       OS << " for instruction: " << Inst << "\n";
 119     }
 120   }
 121 }
 122
 123 PreservedAnalyses CostModelPrinterPass::run(Function &F,
 124                                             FunctionAnalysisManager &AM) {
 125   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
 126   OS << "Printing analysis 'Cost Model Analysis' for function '" << F.getName() << "':\n";
 127   for (BasicBlock &B : F) {
 128     for (Instruction &Inst : B) {
 129       // TODO: Use a pass parameter instead of cl::opt CostKind to determine
 130       // which cost kind to print.
 131       InstructionCost Cost;
 132       auto *II = dyn_cast<IntrinsicInst>(&Inst);
 133       if (II && TypeBasedIntrinsicCost) {
 134         IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II,
 135                                     InstructionCost::getInvalid(), true);
 136         Cost = TTI.getIntrinsicInstrCost(ICA, CostKind);
 137       }
 138       else {
 139         Cost = TTI.getInstructionCost(&Inst, CostKind);
 140       }
 141
 142       if (auto CostVal = Cost.getValue())
 143         OS << "Cost Model: Found an estimated cost of " << *CostVal;
 144       else
 145         OS << "Cost Model: Invalid cost";
 146
 147       OS << " for instruction: " << Inst << "\n";
 148     }
 149   }
 150   return PreservedAnalyses::all();
 151 }