1 //===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
18 //===----------------------------------------------------------------------===//
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/IR/Instructions.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Support/CommandLine.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/raw_ostream.h"
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")));
41 #define CM_NAME "cost-model"
42 #define DEBUG_TYPE CM_NAME
45 class CostModelAnalysis : public FunctionPass {
48 static char ID; // Class identification, replacement for typeinfo
49 CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
50 initializeCostModelAnalysisPass(
51 *PassRegistry::getPassRegistry());
54 /// Returns the expected cost of the instruction.
55 /// Returns -1 if the cost is unknown.
56 /// Note, this method does not cache the cost calculation and it
57 /// can be expensive in some cases.
58 unsigned getInstructionCost(const Instruction *I) const {
59 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
63 void getAnalysisUsage(AnalysisUsage &AU) const override;
64 bool runOnFunction(Function &F) override;
65 void print(raw_ostream &OS, const Module*) const override;
67 /// The function that we analyze.
69 /// Target information.
70 const TargetTransformInfo *TTI;
72 } // End of anonymous namespace
74 // Register this pass.
75 char CostModelAnalysis::ID = 0;
76 static const char cm_name[] = "Cost Model Analysis";
77 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
78 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
80 FunctionPass *llvm::createCostModelAnalysisPass() {
81 return new CostModelAnalysis();
85 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
90 CostModelAnalysis::runOnFunction(Function &F) {
92 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
93 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
98 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
102 for (BasicBlock &B : *F) {
103 for (Instruction &Inst : B) {
104 unsigned Cost = TTI->getInstructionCost(&Inst, CostKind);
105 if (Cost != (unsigned)-1)
106 OS << "Cost Model: Found an estimated cost of " << Cost;
108 OS << "Cost Model: Unknown cost";
110 OS << " for instruction: " << Inst << "\n";