Line data    Source code

       1             : //===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This file defines the cost model analysis. It provides a very basic cost
      11             : // estimation for LLVM-IR. This analysis uses the services of the codegen
      12             : // to approximate the cost of any IR instruction when lowered to machine
      13             : // instructions. The cost results are unit-less and the cost number represents
      14             : // the throughput of the machine assuming that all loads hit the cache, all
      15             : // branches are predicted, etc. The cost numbers can be added in order to
      16             : // compare two or more transformation alternatives.
      17             : //
      18             : //===----------------------------------------------------------------------===//
      19             : 
      20             : #include "llvm/ADT/STLExtras.h"
      21             : #include "llvm/Analysis/Passes.h"
      22             : #include "llvm/Analysis/TargetTransformInfo.h"
      23             : #include "llvm/IR/Function.h"
      24             : #include "llvm/Pass.h"
      25             : #include "llvm/Support/CommandLine.h"
      26             : #include "llvm/Support/Debug.h"
      27             : #include "llvm/Support/raw_ostream.h"
      28             : using namespace llvm;
      29             : 
      30             : static cl::opt<TargetTransformInfo::TargetCostKind> CostKind(
      31             :     "cost-kind", cl::desc("Target cost kind"),
      32             :     cl::init(TargetTransformInfo::TCK_RecipThroughput),
      33             :     cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput,
      34             :                           "throughput", "Reciprocal throughput"),
      35             :                clEnumValN(TargetTransformInfo::TCK_Latency,
      36             :                           "latency", "Instruction latency"),
      37             :                clEnumValN(TargetTransformInfo::TCK_CodeSize,
      38             :                           "code-size", "Code size")));
      39             : 
      40             : #define CM_NAME "cost-model"
      41             : #define DEBUG_TYPE CM_NAME
      42             : 
      43             : namespace {
      44             :   class CostModelAnalysis : public FunctionPass {
      45             : 
      46             :   public:
      47             :     static char ID; // Class identification, replacement for typeinfo
      48         405 :     CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
      49         405 :       initializeCostModelAnalysisPass(
      50         405 :         *PassRegistry::getPassRegistry());
      51         405 :     }
      52             : 
      53             :     /// Returns the expected cost of the instruction.
      54             :     /// Returns -1 if the cost is unknown.
      55             :     /// Note, this method does not cache the cost calculation and it
      56             :     /// can be expensive in some cases.
      57             :     unsigned getInstructionCost(const Instruction *I) const {
      58             :       return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
      59             :     }
      60             : 
      61             :   private:
      62             :     void getAnalysisUsage(AnalysisUsage &AU) const override;
      63             :     bool runOnFunction(Function &F) override;
      64             :     void print(raw_ostream &OS, const Module*) const override;
      65             : 
      66             :     /// The function that we analyze.
      67             :     Function *F;
      68             :     /// Target information.
      69             :     const TargetTransformInfo *TTI;
      70             :   };
      71             : }  // End of anonymous namespace
      72             : 
      73             : // Register this pass.
      74             : char CostModelAnalysis::ID = 0;
      75             : static const char cm_name[] = "Cost Model Analysis";
      76       10756 : INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
      77       21917 : INITIALIZE_PASS_END  (CostModelAnalysis, CM_NAME, cm_name, false, true)
      78             : 
      79           0 : FunctionPass *llvm::createCostModelAnalysisPass() {
      80           0 :   return new CostModelAnalysis();
      81             : }
      82             : 
      83             : void
      84         405 : CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
      85             :   AU.setPreservesAll();
      86         405 : }
      87             : 
      88             : bool
      89        6773 : CostModelAnalysis::runOnFunction(Function &F) {
      90        6773 :  this->F = &F;
      91        6773 :  auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
      92        6773 :  TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
      93             : 
      94        6773 :  return false;
      95             : }
      96             : 
      97        6773 : void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
      98        6773 :   if (!F)
      99             :     return;
     100             : 
     101       13571 :   for (BasicBlock &B : *F) {
     102       34568 :     for (Instruction &Inst : B) {
     103       55540 :       unsigned Cost = TTI->getInstructionCost(&Inst, CostKind);
     104       27770 :       if (Cost != (unsigned)-1)
     105       27769 :         OS << "Cost Model: Found an estimated cost of " << Cost;
     106             :       else
     107           1 :         OS << "Cost Model: Unknown cost";
     108             : 
     109       27770 :       OS << " for instruction: " << Inst << "\n";
     110             :     }
     111             :   }
     112             : }