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/TargetTransformInfo.h"
  21 #include "llvm/IR/Function.h"
  22 #include "llvm/IR/IntrinsicInst.h"
  23 #include "llvm/IR/PassManager.h"
  24 #include "llvm/Pass.h"
  25 #include "llvm/Support/CommandLine.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                clEnumValN(TargetTransformInfo::TCK_SizeAndLatency,
  39                           "size-latency", "Code size and latency")));
  40
  41 static cl::opt<bool> TypeBasedIntrinsicCost("type-based-intrinsic-cost",
  42     cl::desc("Calculate intrinsics cost based only on argument types"),
  43     cl::init(false));
  44
  45 #define CM_NAME "cost-model"
  46 #define DEBUG_TYPE CM_NAME
  47
  48 PreservedAnalyses CostModelPrinterPass::run(Function &F,
  49                                             FunctionAnalysisManager &AM) {
  50   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
  51   OS << "Printing analysis 'Cost Model Analysis' for function '" << F.getName() << "':\n";
  52   for (BasicBlock &B : F) {
  53     for (Instruction &Inst : B) {
  54       // TODO: Use a pass parameter instead of cl::opt CostKind to determine
  55       // which cost kind to print.
  56       InstructionCost Cost;
  57       auto *II = dyn_cast<IntrinsicInst>(&Inst);
  58       if (II && TypeBasedIntrinsicCost) {
  59         IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II,
  60                                     InstructionCost::getInvalid(), true);
  61         Cost = TTI.getIntrinsicInstrCost(ICA, CostKind);
  62       }
  63       else {
  64         Cost = TTI.getInstructionCost(&Inst, CostKind);
  65       }
  66
  67       if (auto CostVal = Cost.getValue())
  68         OS << "Cost Model: Found an estimated cost of " << *CostVal;
  69       else
  70         OS << "Cost Model: Invalid cost";
  71
  72       OS << " for instruction: " << Inst << "\n";
  73     }
  74   }
  75   return PreservedAnalyses::all();
  76 }