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//===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the cost model analysis. It provides a very basic cost
// estimation for LLVM-IR. This analysis uses the services of the codegen
// to approximate the cost of any IR instruction when lowered to machine
// instructions. The cost results are unit-less and the cost number represents
// the throughput of the machine assuming that all loads hit the cache, all
// branches are predicted, etc. The cost numbers can be added in order to
// compare two or more transformation alternatives.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
static cl::opt<TargetTransformInfo::TargetCostKind> CostKind(
"cost-kind", cl::desc("Target cost kind"),
cl::init(TargetTransformInfo::TCK_RecipThroughput),
cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput,
"throughput", "Reciprocal throughput"),
clEnumValN(TargetTransformInfo::TCK_Latency,
"latency", "Instruction latency"),
clEnumValN(TargetTransformInfo::TCK_CodeSize,
"code-size", "Code size"),
clEnumValN(TargetTransformInfo::TCK_SizeAndLatency,
"size-latency", "Code size and latency")));
#define CM_NAME "cost-model"
#define DEBUG_TYPE CM_NAME
namespace {
class CostModelAnalysis : public FunctionPass {
public:
static char ID; // Class identification, replacement for typeinfo
CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
initializeCostModelAnalysisPass(
*PassRegistry::getPassRegistry());
}
/// Returns the expected cost of the instruction.
/// Returns -1 if the cost is unknown.
/// Note, this method does not cache the cost calculation and it
/// can be expensive in some cases.
InstructionCost getInstructionCost(const Instruction *I) const {
return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
}
private:
void getAnalysisUsage(AnalysisUsage &AU) const override;
bool runOnFunction(Function &F) override;
void print(raw_ostream &OS, const Module*) const override;
/// The function that we analyze.
Function *F;
/// Target information.
const TargetTransformInfo *TTI;
};
} // End of anonymous namespace
// Register this pass.
char CostModelAnalysis::ID = 0;
static const char cm_name[] = "Cost Model Analysis";
INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
FunctionPass *llvm::createCostModelAnalysisPass() {
return new CostModelAnalysis();
}
void
CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
}
bool
CostModelAnalysis::runOnFunction(Function &F) {
this->F = &F;
auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
return false;
}
void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
if (!F)
return;
for (BasicBlock &B : *F) {
for (Instruction &Inst : B) {
InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind);
if (auto CostVal = Cost.getValue())
OS << "Cost Model: Found an estimated cost of " << *CostVal;
else
OS << "Cost Model: Unknown cost";
OS << " for instruction: " << Inst << "\n";
}
}
}
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