llvm-project/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

//===-- BenchmarkRunner.cpp -------------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include <array>
#include <memory>
#include <string>

#include "Assembler.h"
#include "BenchmarkRunner.h"
#include "Error.h"
#include "MCInstrDescView.h"
#include "PerfHelper.h"
#include "Target.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Program.h"

namespace llvm {
namespace exegesis {

BenchmarkRunner::BenchmarkRunner(const LLVMState &State,
                                 InstructionBenchmark::ModeE Mode,
                                 BenchmarkPhaseSelectorE BenchmarkPhaseSelector)
    : State(State), Mode(Mode), BenchmarkPhaseSelector(BenchmarkPhaseSelector),
      Scratch(std::make_unique<ScratchSpace>()) {}

BenchmarkRunner::~BenchmarkRunner() = default;

namespace {
class FunctionExecutorImpl : public BenchmarkRunner::FunctionExecutor {
public:
  FunctionExecutorImpl(const LLVMState &State,
                       object::OwningBinary<object::ObjectFile> Obj,
                       BenchmarkRunner::ScratchSpace *Scratch)
      : State(State), Function(State.createTargetMachine(), std::move(Obj)),
        Scratch(Scratch) {}

private:
  Expected<int64_t> runAndMeasure(const char *Counters) const override {
    auto ResultOrError = runAndSample(Counters);
    if (ResultOrError)
      return ResultOrError.get()[0];
    return ResultOrError.takeError();
  }

  static void
  accumulateCounterValues(const llvm::SmallVector<int64_t, 4> &NewValues,
                          llvm::SmallVector<int64_t, 4> *Result) {
    const size_t NumValues = std::max(NewValues.size(), Result->size());
    if (NumValues > Result->size())
      Result->resize(NumValues, 0);
    for (size_t I = 0, End = NewValues.size(); I < End; ++I)
      (*Result)[I] += NewValues[I];
  }

  Expected<llvm::SmallVector<int64_t, 4>>
  runAndSample(const char *Counters) const override {
    // We sum counts when there are several counters for a single ProcRes
    // (e.g. P23 on SandyBridge).
    llvm::SmallVector<int64_t, 4> CounterValues;
    int Reserved = 0;
    SmallVector<StringRef, 2> CounterNames;
    StringRef(Counters).split(CounterNames, '+');
    char *const ScratchPtr = Scratch->ptr();
    const ExegesisTarget &ET = State.getExegesisTarget();
    for (auto &CounterName : CounterNames) {
      CounterName = CounterName.trim();
      auto CounterOrError = ET.createCounter(CounterName, State);

      if (!CounterOrError)
        return CounterOrError.takeError();

      pfm::Counter *Counter = CounterOrError.get().get();
      if (Reserved == 0) {
        Reserved = Counter->numValues();
        CounterValues.reserve(Reserved);
      } else if (Reserved != Counter->numValues())
        // It'd be wrong to accumulate vectors of different sizes.
        return make_error<Failure>(
            llvm::Twine("Inconsistent number of values for counter ")
                .concat(CounterName)
                .concat(std::to_string(Counter->numValues()))
                .concat(" vs expected of ")
                .concat(std::to_string(Reserved)));
      Scratch->clear();
      {
        auto PS = ET.withSavedState();
        CrashRecoveryContext CRC;
        CrashRecoveryContext::Enable();
        const bool Crashed = !CRC.RunSafely([this, Counter, ScratchPtr]() {
          Counter->start();
          this->Function(ScratchPtr);
          Counter->stop();
        });
        CrashRecoveryContext::Disable();
        PS.reset();
        if (Crashed) {
          std::string Msg = "snippet crashed while running";
#ifdef LLVM_ON_UNIX
          // See "Exit Status for Commands":
          // https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html
          constexpr const int kSigOffset = 128;
          if (const char *const SigName = strsignal(CRC.RetCode - kSigOffset)) {
            Msg += ": ";
            Msg += SigName;
          }
#endif
          return make_error<SnippetCrash>(std::move(Msg));
        }
      }

      auto ValueOrError = Counter->readOrError(Function.getFunctionBytes());
      if (!ValueOrError)
        return ValueOrError.takeError();
      accumulateCounterValues(ValueOrError.get(), &CounterValues);
    }
    return CounterValues;
  }

  const LLVMState &State;
  const ExecutableFunction Function;
  BenchmarkRunner::ScratchSpace *const Scratch;
};
} // namespace

Expected<SmallString<0>> BenchmarkRunner::assembleSnippet(
    const BenchmarkCode &BC, const SnippetRepetitor &Repetitor,
    unsigned MinInstructions, unsigned LoopBodySize) const {
  const std::vector<MCInst> &Instructions = BC.Key.Instructions;
  SmallString<0> Buffer;
  raw_svector_ostream OS(Buffer);
  if (Error E = assembleToStream(
          State.getExegesisTarget(), State.createTargetMachine(), BC.LiveIns,
          BC.Key.RegisterInitialValues,
          Repetitor.Repeat(Instructions, MinInstructions, LoopBodySize), OS)) {
    return std::move(E);
  }
  return Buffer;
}

Expected<BenchmarkRunner::RunnableConfiguration>
BenchmarkRunner::getRunnableConfiguration(
    const BenchmarkCode &BC, unsigned NumRepetitions, unsigned LoopBodySize,
    const SnippetRepetitor &Repetitor) const {
  RunnableConfiguration RC;

  InstructionBenchmark &InstrBenchmark = RC.InstrBenchmark;
  InstrBenchmark.Mode = Mode;
  InstrBenchmark.CpuName = std::string(State.getTargetMachine().getTargetCPU());
  InstrBenchmark.LLVMTriple =
      State.getTargetMachine().getTargetTriple().normalize();
  InstrBenchmark.NumRepetitions = NumRepetitions;
  InstrBenchmark.Info = BC.Info;

  const std::vector<MCInst> &Instructions = BC.Key.Instructions;

  InstrBenchmark.Key = BC.Key;

  // Assemble at least kMinInstructionsForSnippet instructions by repeating
  // the snippet for debug/analysis. This is so that the user clearly
  // understands that the inside instructions are repeated.
  if (BenchmarkPhaseSelector > BenchmarkPhaseSelectorE::PrepareSnippet) {
    const int MinInstructionsForSnippet = 4 * Instructions.size();
    const int LoopBodySizeForSnippet = 2 * Instructions.size();
    auto Snippet = assembleSnippet(BC, Repetitor, MinInstructionsForSnippet,
                                   LoopBodySizeForSnippet);
    if (Error E = Snippet.takeError())
      return std::move(E);
    const ExecutableFunction EF(State.createTargetMachine(),
                                getObjectFromBuffer(*Snippet));
    const auto FnBytes = EF.getFunctionBytes();
    llvm::append_range(InstrBenchmark.AssembledSnippet, FnBytes);
  }

  // Assemble NumRepetitions instructions repetitions of the snippet for
  // measurements.
  if (BenchmarkPhaseSelector > BenchmarkPhaseSelectorE::PrepareAndAssembleSnippet) {
    auto Snippet = assembleSnippet(BC, Repetitor, InstrBenchmark.NumRepetitions,
                                   LoopBodySize);
    if (Error E = Snippet.takeError())
      return std::move(E);
    RC.ObjectFile = getObjectFromBuffer(*Snippet);
  }

  return std::move(RC);
}

Expected<InstructionBenchmark>
BenchmarkRunner::runConfiguration(RunnableConfiguration &&RC,
                                  bool DumpObjectToDisk) const {
  InstructionBenchmark &InstrBenchmark = RC.InstrBenchmark;
  object::OwningBinary<object::ObjectFile> &ObjectFile = RC.ObjectFile;

  if (DumpObjectToDisk &&
      BenchmarkPhaseSelector > BenchmarkPhaseSelectorE::PrepareAndAssembleSnippet) {
    auto ObjectFilePath = writeObjectFile(ObjectFile.getBinary()->getData());
    if (Error E = ObjectFilePath.takeError()) {
      InstrBenchmark.Error = toString(std::move(E));
      return std::move(InstrBenchmark);
    }
    outs() << "Check generated assembly with: /usr/bin/objdump -d "
           << *ObjectFilePath << "\n";
  }

  if (BenchmarkPhaseSelector < BenchmarkPhaseSelectorE::Measure) {
    InstrBenchmark.Error = "actual measurements skipped.";
    return std::move(InstrBenchmark);
  }

  const FunctionExecutorImpl Executor(State, std::move(ObjectFile),
                                      Scratch.get());
  auto NewMeasurements = runMeasurements(Executor);
  if (Error E = NewMeasurements.takeError()) {
    if (!E.isA<SnippetCrash>())
      return std::move(E);
    InstrBenchmark.Error = toString(std::move(E));
    return std::move(InstrBenchmark);
  }
  assert(InstrBenchmark.NumRepetitions > 0 && "invalid NumRepetitions");
  for (BenchmarkMeasure &BM : *NewMeasurements) {
    // Scale the measurements by instruction.
    BM.PerInstructionValue /= InstrBenchmark.NumRepetitions;
    // Scale the measurements by snippet.
    BM.PerSnippetValue *=
        static_cast<double>(InstrBenchmark.Key.Instructions.size()) /
        InstrBenchmark.NumRepetitions;
  }
  InstrBenchmark.Measurements = std::move(*NewMeasurements);

  return std::move(InstrBenchmark);
}

Expected<std::string> BenchmarkRunner::writeObjectFile(StringRef Buffer) const {
  int ResultFD = 0;
  SmallString<256> ResultPath;
  if (Error E = errorCodeToError(
          sys::fs::createTemporaryFile("snippet", "o", ResultFD, ResultPath)))
    return std::move(E);
  raw_fd_ostream OFS(ResultFD, true /*ShouldClose*/);
  OFS.write(Buffer.data(), Buffer.size());
  OFS.flush();
  return std::string(ResultPath.str());
}

BenchmarkRunner::FunctionExecutor::~FunctionExecutor() {}

} // namespace exegesis
} // namespace llvm