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/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/PassManager.h"
25 #include "llvm/InitializePasses.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Support/CommandLine.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/raw_ostream.h"
30 using namespace llvm;
31
32 static cl::opt<TargetTransformInfo::TargetCostKind> CostKind(
33 "cost-kind", cl::desc("Target cost kind"),
34 cl::init(TargetTransformInfo::TCK_RecipThroughput),
35 cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput,
36 "throughput", "Reciprocal throughput"),
37 clEnumValN(TargetTransformInfo::TCK_Latency,
38 "latency", "Instruction latency"),
39 clEnumValN(TargetTransformInfo::TCK_CodeSize,
40 "code-size", "Code size"),
41 clEnumValN(TargetTransformInfo::TCK_SizeAndLatency,
42 "size-latency", "Code size and latency")));
43
44
45 #define CM_NAME "cost-model"
46 #define DEBUG_TYPE CM_NAME
47
48 namespace {
49 class CostModelAnalysis : public FunctionPass {
50
51 public:
52 static char ID; // Class identification, replacement for typeinfo
CostModelAnalysis()53 CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
54 initializeCostModelAnalysisPass(
55 *PassRegistry::getPassRegistry());
56 }
57
58 /// Returns the expected cost of the instruction.
59 /// Returns -1 if the cost is unknown.
60 /// Note, this method does not cache the cost calculation and it
61 /// can be expensive in some cases.
getInstructionCost(const Instruction * I) const62 InstructionCost getInstructionCost(const Instruction *I) const {
63 return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
64 }
65
66 private:
67 void getAnalysisUsage(AnalysisUsage &AU) const override;
68 bool runOnFunction(Function &F) override;
69 void print(raw_ostream &OS, const Module*) const override;
70
71 /// The function that we analyze.
72 Function *F;
73 /// Target information.
74 const TargetTransformInfo *TTI;
75 };
76 } // End of anonymous namespace
77
78 // Register this pass.
79 char CostModelAnalysis::ID = 0;
80 static const char cm_name[] = "Cost Model Analysis";
INITIALIZE_PASS_BEGIN(CostModelAnalysis,CM_NAME,cm_name,false,true)81 INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
82 INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
83
84 FunctionPass *llvm::createCostModelAnalysisPass() {
85 return new CostModelAnalysis();
86 }
87
88 void
getAnalysisUsage(AnalysisUsage & AU) const89 CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
90 AU.setPreservesAll();
91 }
92
93 bool
runOnFunction(Function & F)94 CostModelAnalysis::runOnFunction(Function &F) {
95 this->F = &F;
96 auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
97 TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
98
99 return false;
100 }
101
print(raw_ostream & OS,const Module *) const102 void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
103 if (!F)
104 return;
105
106 for (BasicBlock &B : *F) {
107 for (Instruction &Inst : B) {
108 InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind);
109 if (auto CostVal = Cost.getValue())
110 OS << "Cost Model: Found an estimated cost of " << *CostVal;
111 else
112 OS << "Cost Model: Invalid cost";
113
114 OS << " for instruction: " << Inst << "\n";
115 }
116 }
117 }
118
run(Function & F,FunctionAnalysisManager & AM)119 PreservedAnalyses CostModelPrinterPass::run(Function &F,
120 FunctionAnalysisManager &AM) {
121 auto &TTI = AM.getResult<TargetIRAnalysis>(F);
122 OS << "Cost Model for function '" << F.getName() << "'\n";
123 for (BasicBlock &B : F) {
124 for (Instruction &Inst : B) {
125 // TODO: Use a pass parameter instead of cl::opt CostKind to determine
126 // which cost kind to print.
127 InstructionCost Cost = TTI.getInstructionCost(&Inst, CostKind);
128 if (auto CostVal = Cost.getValue())
129 OS << "Cost Model: Found an estimated cost of " << *CostVal;
130 else
131 OS << "Cost Model: Invalid cost";
132
133 OS << " for instruction: " << Inst << "\n";
134 }
135 }
136 return PreservedAnalyses::all();
137 }
138