llvm/tools/llvm-exegesis/lib/ParallelSnippetGenerator.h

//===-- ParallelSnippetGenerator.h ------------------------------*- 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// A SnippetGenerator implementation to create parallel instruction snippets.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_TOOLS_LLVM_EXEGESIS_PARALLELSNIPPETGENERATOR_H
#define LLVM_TOOLS_LLVM_EXEGESIS_PARALLELSNIPPETGENERATOR_H

#include "SnippetGenerator.h"

namespace llvm {
namespace exegesis {

class ParallelSnippetGenerator : public SnippetGenerator {
public:
  using SnippetGenerator::SnippetGenerator;
  ~ParallelSnippetGenerator() override;

  Expected<std::vector<CodeTemplate>>
  generateCodeTemplates(InstructionTemplate Variant,
                        const BitVector &ForbiddenRegisters) const override;

  static constexpr const size_t kMinNumDifferentAddresses = 6;

private:
  // Instantiates memory operands within a snippet.
  // To make computations as parallel as possible, we generate independant
  // memory locations for instructions that load and store. If there are less
  // than kMinNumDifferentAddresses in the original snippet, we duplicate
  // instructions until there are this number of instructions.
  // For example, assuming kMinNumDifferentAddresses=5 and
  // getMaxMemoryAccessSize()=64, if the original snippet is:
  //   mov eax, [memory]
  // we might generate:
  //   mov eax, [rdi]
  //   mov eax, [rdi + 64]
  //   mov eax, [rdi + 128]
  //   mov eax, [rdi + 192]
  //   mov eax, [rdi + 256]
  // If the original snippet is:
  //   mov eax, [memory]
  //   add eax, [memory]
  // we might generate:
  //   mov eax, [rdi]
  //   add eax, [rdi + 64]
  //   mov eax, [rdi + 128]
  //   add eax, [rdi + 192]
  //   mov eax, [rdi + 256]
  void instantiateMemoryOperands(
      unsigned ScratchSpaceReg,
      std::vector<InstructionTemplate> &SnippetTemplate) const;
};

} // namespace exegesis
} // namespace llvm

#endif // LLVM_TOOLS_LLVM_EXEGESIS_PARALLELSNIPPETGENERATOR_H