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 PreservedAnalyses CostModelPrinterPass::run(Function &F,
  51                                             FunctionAnalysisManager &AM) {
  52   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
  53   OS << "Printing analysis 'Cost Model Analysis' for function '" << F.getName() << "':\n";
  54   for (BasicBlock &B : F) {
  55     for (Instruction &Inst : B) {
  56       // TODO: Use a pass parameter instead of cl::opt CostKind to determine
  57       // which cost kind to print.
  58       InstructionCost Cost;
  59       auto *II = dyn_cast<IntrinsicInst>(&Inst);
  60       if (II && TypeBasedIntrinsicCost) {
  61         IntrinsicCostAttributes ICA(II->getIntrinsicID(), *II,
  62                                     InstructionCost::getInvalid(), true);
  63         Cost = TTI.getIntrinsicInstrCost(ICA, CostKind);
  64       }
  65       else {
  66         Cost = TTI.getInstructionCost(&Inst, CostKind);
  67       }
  68
  69       if (auto CostVal = Cost.getValue())
  70         OS << "Cost Model: Found an estimated cost of " << *CostVal;
  71       else
  72         OS << "Cost Model: Invalid cost";
  73
  74       OS << " for instruction: " << Inst << "\n";
  75     }
  76   }
  77   return PreservedAnalyses::all();
  78 }