4a9fdda988
Currently MCA takes instruction properties from scheduling model. However, some instructions may execute differently depending on external factors - for example, latency of memory instructions may vary differently depending on whether the load comes from L1 cache, L2 or DRAM. While MCA as a static analysis tool cannot model such differences (and currently takes some static decision, e.g. all memory ops are treated as L1 accesses), it makes sense to allow manual modification of instruction properties to model different behavior (e.g. sensitivity of code performance to cache misses in particular load instruction). This patch addresses this need. The library modification is intentionally generic - arbitrary modifications to InstrDesc are allowed. The tool support is currently limited to changing instruction latencies (single number applies to all output arguments and MaxLatency) via coments in the input assembler code; the format is the like this: add (%eax), eax // LLVM-MCA-LATENCY:100 Users of MCA library can already make additional customizations; command line tool can be extended in the future. Note that InstructionView currently shows per-instruction information according to scheduling model and is not affected by this change. See https://github.com/llvm/llvm-project/issues/133429 for additional clarifications (including explanation why existing customization mechanisms do not provide required functionality) --------- Co-authored-by: Min-Yih Hsu <min@myhsu.dev>
100 lines
3.2 KiB
C++
100 lines
3.2 KiB
C++
//===--------------------- CustomBehaviour.cpp ------------------*- C++ -*-===//
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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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/// \file
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///
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/// This file implements methods from the CustomBehaviour interface.
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///
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//===----------------------------------------------------------------------===//
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#include "llvm/MCA/CustomBehaviour.h"
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#include "llvm/MCA/Instruction.h"
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namespace llvm {
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namespace mca {
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CustomBehaviour::~CustomBehaviour() = default;
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unsigned CustomBehaviour::checkCustomHazard(ArrayRef<InstRef> IssuedInst,
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const InstRef &IR) {
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// 0 signifies that there are no hazards that need to be waited on
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return 0;
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}
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std::vector<std::unique_ptr<View>>
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CustomBehaviour::getStartViews(llvm::MCInstPrinter &IP,
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llvm::ArrayRef<llvm::MCInst> Insts) {
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return std::vector<std::unique_ptr<View>>();
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}
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std::vector<std::unique_ptr<View>>
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CustomBehaviour::getPostInstrInfoViews(llvm::MCInstPrinter &IP,
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llvm::ArrayRef<llvm::MCInst> Insts) {
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return std::vector<std::unique_ptr<View>>();
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}
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std::vector<std::unique_ptr<View>>
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CustomBehaviour::getEndViews(llvm::MCInstPrinter &IP,
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llvm::ArrayRef<llvm::MCInst> Insts) {
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return std::vector<std::unique_ptr<View>>();
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}
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const llvm::StringRef LatencyInstrument::DESC_NAME = "LATENCY";
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bool InstrumentManager::supportsInstrumentType(StringRef Type) const {
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return EnableInstruments && Type == LatencyInstrument::DESC_NAME;
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}
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bool InstrumentManager::canCustomize(const ArrayRef<Instrument *> IVec) const {
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for (const auto I : IVec) {
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if (I->getDesc() == LatencyInstrument::DESC_NAME) {
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auto LatInst = static_cast<LatencyInstrument *>(I);
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return LatInst->hasValue();
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}
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}
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return false;
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}
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void InstrumentManager::customize(const ArrayRef<Instrument *> IVec,
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InstrDesc &ID) const {
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for (const auto I : IVec) {
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if (I->getDesc() == LatencyInstrument::DESC_NAME) {
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auto LatInst = static_cast<LatencyInstrument *>(I);
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if (LatInst->hasValue()) {
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unsigned Latency = LatInst->getLatency();
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// TODO Allow to customize a subset of ID.Writes
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for (auto &W : ID.Writes)
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W.Latency = Latency;
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ID.MaxLatency = Latency;
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}
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}
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}
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}
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UniqueInstrument InstrumentManager::createInstrument(StringRef Desc,
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StringRef Data) {
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if (EnableInstruments) {
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if (Desc == LatencyInstrument::DESC_NAME)
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return std::make_unique<LatencyInstrument>(Data);
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}
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return std::make_unique<Instrument>(Desc, Data);
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}
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SmallVector<UniqueInstrument>
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InstrumentManager::createInstruments(const MCInst &Inst) {
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return SmallVector<UniqueInstrument>();
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}
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unsigned InstrumentManager::getSchedClassID(
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const MCInstrInfo &MCII, const MCInst &MCI,
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const llvm::SmallVector<Instrument *> &IVec) const {
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return MCII.get(MCI.getOpcode()).getSchedClass();
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}
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} // namespace mca
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} // namespace llvm
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