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76e5989934
We previously made a change to getUserCost to return a Invalid cost when one of the TTI costs returned '-1' (meaning 'unknown' or 'infinitely expensive'). It makes no sense to say that: shufflevector <2 x i8> %x, <2 x i8> %y, <4 x i32> <i32 0, i32 1, i32 2, i32 3> has an invalid cost. Perhaps the cost is not known, but the IR is valid and can be code-generated. Invalid should only be used for IR that cannot possibly be code-generated and where a cost is nonsensical. With more passes now asserting that the cost must be valid, it is possible that those assertions will fail for perfectly valid IR. An incomplete cost-model probably shouldn't be a reason for the compiler to break. It's better to consider these costs as 'very expensive' and ignore them for other reasons. At some point, we should consider replacing -1 with some other mechanism. Reviewed By: paulwalker-arm, dmgreen Differential Revision: https://reviews.llvm.org/D99502
116 lines
4.0 KiB
C++
116 lines
4.0 KiB
C++
//===- CostModel.cpp ------ Cost Model Analysis ---------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the cost model analysis. It provides a very basic cost
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// estimation for LLVM-IR. This analysis uses the services of the codegen
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// to approximate the cost of any IR instruction when lowered to machine
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// instructions. The cost results are unit-less and the cost number represents
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// the throughput of the machine assuming that all loads hit the cache, all
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// branches are predicted, etc. The cost numbers can be added in order to
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// compare two or more transformation alternatives.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/Function.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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static cl::opt<TargetTransformInfo::TargetCostKind> CostKind(
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"cost-kind", cl::desc("Target cost kind"),
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cl::init(TargetTransformInfo::TCK_RecipThroughput),
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cl::values(clEnumValN(TargetTransformInfo::TCK_RecipThroughput,
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"throughput", "Reciprocal throughput"),
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clEnumValN(TargetTransformInfo::TCK_Latency,
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"latency", "Instruction latency"),
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clEnumValN(TargetTransformInfo::TCK_CodeSize,
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"code-size", "Code size"),
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clEnumValN(TargetTransformInfo::TCK_SizeAndLatency,
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"size-latency", "Code size and latency")));
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#define CM_NAME "cost-model"
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#define DEBUG_TYPE CM_NAME
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namespace {
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class CostModelAnalysis : public FunctionPass {
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public:
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static char ID; // Class identification, replacement for typeinfo
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CostModelAnalysis() : FunctionPass(ID), F(nullptr), TTI(nullptr) {
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initializeCostModelAnalysisPass(
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*PassRegistry::getPassRegistry());
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}
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/// Returns the expected cost of the instruction.
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/// Returns -1 if the cost is unknown.
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/// Note, this method does not cache the cost calculation and it
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/// can be expensive in some cases.
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InstructionCost getInstructionCost(const Instruction *I) const {
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return TTI->getInstructionCost(I, TargetTransformInfo::TCK_RecipThroughput);
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}
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private:
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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bool runOnFunction(Function &F) override;
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void print(raw_ostream &OS, const Module*) const override;
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/// The function that we analyze.
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Function *F;
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/// Target information.
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const TargetTransformInfo *TTI;
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};
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} // End of anonymous namespace
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// Register this pass.
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char CostModelAnalysis::ID = 0;
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static const char cm_name[] = "Cost Model Analysis";
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INITIALIZE_PASS_BEGIN(CostModelAnalysis, CM_NAME, cm_name, false, true)
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INITIALIZE_PASS_END (CostModelAnalysis, CM_NAME, cm_name, false, true)
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FunctionPass *llvm::createCostModelAnalysisPass() {
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return new CostModelAnalysis();
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}
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void
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CostModelAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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}
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bool
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CostModelAnalysis::runOnFunction(Function &F) {
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this->F = &F;
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auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
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TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
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return false;
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}
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void CostModelAnalysis::print(raw_ostream &OS, const Module*) const {
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if (!F)
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return;
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for (BasicBlock &B : *F) {
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for (Instruction &Inst : B) {
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InstructionCost Cost = TTI->getInstructionCost(&Inst, CostKind);
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if (auto CostVal = Cost.getValue())
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OS << "Cost Model: Found an estimated cost of " << *CostVal;
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else
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OS << "Cost Model: Invalid cost";
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OS << " for instruction: " << Inst << "\n";
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}
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}
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}
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