CostModel.cpp revision 243789 
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. The cost result can be thought of as cycles, but it
12// is really unit-less. The estimated cost is ment to be used for comparing
13// alternatives.
14//
15//===----------------------------------------------------------------------===//
16
17#define CM_NAME "cost-model"
18#define DEBUG_TYPE CM_NAME
19#include "llvm/Analysis/Passes.h"
20#include "llvm/Function.h"
21#include "llvm/Instructions.h"
22#include "llvm/Pass.h"
23#include "llvm/TargetTransformInfo.h"
24#include "llvm/Value.h"
25#include "llvm/Support/Debug.h"
26#include "llvm/Support/raw_ostream.h"
27using namespace llvm;
28
29namespace {
30  class CostModelAnalysis : public FunctionPass {
31
32  public:
33    static char ID; // Class identification, replacement for typeinfo
34    CostModelAnalysis() : FunctionPass(ID), F(0), VTTI(0) {
35      initializeCostModelAnalysisPass(
36        *PassRegistry::getPassRegistry());
37    }
38
39    /// Returns the expected cost of the instruction.
40    /// Returns -1 if the cost is unknown.
41    /// Note, this method does not cache the cost calculation and it
42    /// can be expensive in some cases.
43    unsigned getInstructionCost(Instruction *I) const;
44
45  private:
46    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
47    virtual bool runOnFunction(Function &F);
48    virtual void print(raw_ostream &OS, const Module*) const;
49
50    /// The function that we analyze.
51    Function *F;
52    /// Vector target information.
53    const VectorTargetTransformInfo *VTTI;
54  };
55}  // End of anonymous namespace
56
57// Register this pass.
58char CostModelAnalysis::ID = 0;
59static const char cm_name[] = "Cost Model Analysis";
60INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
61INITIALIZE_PASS_END  (CostModelAnalysis, CM_NAME, cm_name, false, true)
62
63FunctionPass *llvm::createCostModelAnalysisPass() {
64  return new CostModelAnalysis();
65}
66
67void
68CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
69  AU.setPreservesAll();
70}
71
72bool
73CostModelAnalysis::runOnFunction(Function &F) {
74 this->F = &F;
75
76 // Target information.
77 TargetTransformInfo *TTI;
78 TTI = getAnalysisIfAvailable<TargetTransformInfo>();
79 if (TTI)
80   VTTI = TTI->getVectorTargetTransformInfo();
81
82 return false;
83}
84
85unsigned CostModelAnalysis::getInstructionCost(Instruction *I) const {
86  if (!VTTI)
87    return -1;
88
89  switch (I->getOpcode()) {
90  case Instruction::Ret:
91  case Instruction::PHI:
92  case Instruction::Br: {
93    return VTTI->getCFInstrCost(I->getOpcode());
94  }
95  case Instruction::Add:
96  case Instruction::FAdd:
97  case Instruction::Sub:
98  case Instruction::FSub:
99  case Instruction::Mul:
100  case Instruction::FMul:
101  case Instruction::UDiv:
102  case Instruction::SDiv:
103  case Instruction::FDiv:
104  case Instruction::URem:
105  case Instruction::SRem:
106  case Instruction::FRem:
107  case Instruction::Shl:
108  case Instruction::LShr:
109  case Instruction::AShr:
110  case Instruction::And:
111  case Instruction::Or:
112  case Instruction::Xor: {
113    return VTTI->getArithmeticInstrCost(I->getOpcode(), I->getType());
114  }
115  case Instruction::Select: {
116    SelectInst *SI = cast<SelectInst>(I);
117    Type *CondTy = SI->getCondition()->getType();
118    return VTTI->getCmpSelInstrCost(I->getOpcode(), I->getType(), CondTy);
119  }
120  case Instruction::ICmp:
121  case Instruction::FCmp: {
122    Type *ValTy = I->getOperand(0)->getType();
123    return VTTI->getCmpSelInstrCost(I->getOpcode(), ValTy);
124  }
125  case Instruction::Store: {
126    StoreInst *SI = cast<StoreInst>(I);
127    Type *ValTy = SI->getValueOperand()->getType();
128    return VTTI->getMemoryOpCost(I->getOpcode(), ValTy,
129                                 SI->getAlignment(),
130                                 SI->getPointerAddressSpace());
131  }
132  case Instruction::Load: {
133    LoadInst *LI = cast<LoadInst>(I);
134    return VTTI->getMemoryOpCost(I->getOpcode(), I->getType(),
135                                 LI->getAlignment(),
136                                 LI->getPointerAddressSpace());
137  }
138  case Instruction::ZExt:
139  case Instruction::SExt:
140  case Instruction::FPToUI:
141  case Instruction::FPToSI:
142  case Instruction::FPExt:
143  case Instruction::PtrToInt:
144  case Instruction::IntToPtr:
145  case Instruction::SIToFP:
146  case Instruction::UIToFP:
147  case Instruction::Trunc:
148  case Instruction::FPTrunc:
149  case Instruction::BitCast: {
150    Type *SrcTy = I->getOperand(0)->getType();
151    return VTTI->getCastInstrCost(I->getOpcode(), I->getType(), SrcTy);
152  }
153  case Instruction::ExtractElement: {
154    ExtractElementInst * EEI = cast<ExtractElementInst>(I);
155    ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1));
156    unsigned Idx = -1;
157    if (CI)
158      Idx = CI->getZExtValue();
159    return VTTI->getVectorInstrCost(I->getOpcode(),
160                                    EEI->getOperand(0)->getType(), Idx);
161  }
162  case Instruction::InsertElement: {
163      InsertElementInst * IE = cast<InsertElementInst>(I);
164      ConstantInt *CI = dyn_cast<ConstantInt>(IE->getOperand(2));
165      unsigned Idx = -1;
166      if (CI)
167        Idx = CI->getZExtValue();
168      return VTTI->getVectorInstrCost(I->getOpcode(),
169                                      IE->getType(), Idx);
170    }
171  default:
172    // We don't have any information on this instruction.
173    return -1;
174  }
175}
176
177void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
178  if (!F)
179    return;
180
181  for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
182    for (BasicBlock::iterator it = B->begin(), e = B->end(); it != e; ++it) {
183      Instruction *Inst = it;
184      unsigned Cost = getInstructionCost(Inst);
185      if (Cost != (unsigned)-1)
186        OS << "Cost Model: Found an estimated cost of " << Cost;
187      else
188        OS << "Cost Model: Unknown cost";
189
190      OS << " for instruction: "<< *Inst << "\n";
191    }
192  }
193}
194