tools/llvm-exegesis/lib/BenchmarkRunner.h

//===-- BenchmarkRunner.h ---------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Defines the abstract BenchmarkRunner class for measuring a certain execution
/// property of instructions (e.g. latency).
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H
#define LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H

#include "Assembler.h"
#include "BenchmarkResult.h"
#include "LlvmState.h"
#include "MCInstrDescView.h"
#include "RegisterAliasing.h"
#include "llvm/MC/MCInst.h"
#include "llvm/Support/Error.h"
#include <cstdlib>
#include <memory>
#include <vector>

namespace exegesis {

// A class representing failures that happened during Benchmark, they are used
// to report informations to the user.
class BenchmarkFailure : public llvm::StringError {
public:
  BenchmarkFailure(const llvm::Twine &S);
};

// A collection of instructions that are to be assembled, executed and measured.
struct BenchmarkConfiguration {
  // This code is run before the Snippet is iterated. Since it is part of the
  // measurement it should be as short as possible. It is usually used to setup
  // the content of the Registers.
  struct Setup {
    std::vector<unsigned> LiveIns; // The registers that are live on entry.
    std::vector<unsigned> RegsToDef;
  };
  Setup SnippetSetup;

  // The sequence of instructions that are to be repeated.
  std::vector<llvm::MCInst> Snippet;

  // Informations about how this configuration was built.
  std::string Info;
};

// Common code for all benchmark modes.
class BenchmarkRunner {
public:
  explicit BenchmarkRunner(const LLVMState &State,
                           InstructionBenchmark::ModeE Mode);

  virtual ~BenchmarkRunner();

  llvm::Expected<std::vector<InstructionBenchmark>>
  run(unsigned Opcode, unsigned NumRepetitions);

  // Given a snippet, computes which registers the setup code needs to define.
  std::vector<unsigned>
  computeRegsToDef(const std::vector<InstructionBuilder> &Snippet) const;

  // Scratch space to run instructions that touch memory.
  struct ScratchSpace {
    static constexpr const size_t kAlignment = 1024;
    static constexpr const size_t kSize = 1 << 20; // 1MB.
    ScratchSpace()
        : UnalignedPtr(llvm::make_unique<char[]>(kSize + kAlignment)),
          AlignedPtr(
              UnalignedPtr.get() + kAlignment -
              (reinterpret_cast<intptr_t>(UnalignedPtr.get()) % kAlignment)) {}
    char *ptr() const { return AlignedPtr; }
    void clear() { std::memset(ptr(), 0, kSize); }

  private:
    const std::unique_ptr<char[]> UnalignedPtr;
    char *const AlignedPtr;
  };

protected:
  const LLVMState &State;
  const RegisterAliasingTrackerCache RATC;

  // Generates a single instruction prototype that has a self-dependency.
  llvm::Expected<SnippetPrototype>
  generateSelfAliasingPrototype(const Instruction &Instr) const;
  // Generates a single instruction prototype without assignment constraints.
  llvm::Expected<SnippetPrototype>
  generateUnconstrainedPrototype(const Instruction &Instr,
                                 llvm::StringRef Msg) const;

private:
  // API to be implemented by subclasses.
  virtual llvm::Expected<SnippetPrototype>
  generatePrototype(unsigned Opcode) const = 0;

  virtual std::vector<BenchmarkMeasure>
  runMeasurements(const ExecutableFunction &EF, ScratchSpace &Scratch,
                  const unsigned NumRepetitions) const = 0;

  // Internal helpers.
  InstructionBenchmark runOne(const BenchmarkConfiguration &Configuration,
                              unsigned Opcode, unsigned NumRepetitions) const;

  // Calls generatePrototype and expands the SnippetPrototype into one or more
  // BenchmarkConfiguration.
  llvm::Expected<std::vector<BenchmarkConfiguration>>
  generateConfigurations(unsigned Opcode) const;

  llvm::Expected<std::string>
  writeObjectFile(const BenchmarkConfiguration::Setup &Setup,
                  llvm::ArrayRef<llvm::MCInst> Code) const;

  const InstructionBenchmark::ModeE Mode;

  const std::unique_ptr<ScratchSpace> Scratch;
};

} // namespace exegesis

#endif // LLVM_TOOLS_LLVM_EXEGESIS_BENCHMARKRUNNER_H