tools/llvm-exegesis/lib/SnippetGenerator.h

   1 //===-- SnippetGenerator.h --------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// Defines the abstract SnippetGenerator class for generating code that allows
  11 /// measuring a certain property of instructions (e.g. latency).
  12 ///
  13 //===----------------------------------------------------------------------===//
  14
  15 #ifndef LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
  16 #define LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
  17
  18 #include "Assembler.h"
  19 #include "BenchmarkCode.h"
  20 #include "CodeTemplate.h"
  21 #include "LlvmState.h"
  22 #include "MCInstrDescView.h"
  23 #include "RegisterAliasing.h"
  24 #include "llvm/MC/MCInst.h"
  25 #include "llvm/Support/Error.h"
  26 #include <cstdlib>
  27 #include <memory>
  28 #include <vector>
  29
  30 namespace llvm {
  31 namespace exegesis {
  32
  33 std::vector<CodeTemplate> getSingleton(CodeTemplate &&CT);
  34
  35 // Generates code templates that has a self-dependency.
  36 Expected<std::vector<CodeTemplate>>
  37 generateSelfAliasingCodeTemplates(const Instruction &Instr);
  38
  39 // Generates code templates without assignment constraints.
  40 Expected<std::vector<CodeTemplate>>
  41 generateUnconstrainedCodeTemplates(const Instruction &Instr, StringRef Msg);
  42
  43 // A class representing failures that happened during Benchmark, they are used
  44 // to report informations to the user.
  45 class SnippetGeneratorFailure : public StringError {
  46 public:
  47   SnippetGeneratorFailure(const Twine &S);
  48 };
  49
  50 // Common code for all benchmark modes.
  51 class SnippetGenerator {
  52 public:
  53   struct Options {
  54     unsigned MaxConfigsPerOpcode = 1;
  55   };
  56
  57   explicit SnippetGenerator(const LLVMState &State, const Options &Opts);
  58
  59   virtual ~SnippetGenerator();
  60
  61   // Calls generateCodeTemplate and expands it into one or more BenchmarkCode.
  62   Expected<std::vector<BenchmarkCode>>
  63   generateConfigurations(const Instruction &Instr,
  64                          const BitVector &ExtraForbiddenRegs) const;
  65
  66   // Given a snippet, computes which registers the setup code needs to define.
  67   std::vector<RegisterValue> computeRegisterInitialValues(
  68       const std::vector<InstructionTemplate> &Snippet) const;
  69
  70 protected:
  71   const LLVMState &State;
  72   const Options Opts;
  73
  74 private:
  75   // API to be implemented by subclasses.
  76   virtual Expected<std::vector<CodeTemplate>>
  77   generateCodeTemplates(const Instruction &Instr,
  78                         const BitVector &ForbiddenRegisters) const = 0;
  79 };
  80
  81 // A global Random Number Generator to randomize configurations.
  82 // FIXME: Move random number generation into an object and make it seedable for
  83 // unit tests.
  84 std::mt19937 &randomGenerator();
  85
  86 // Picks a random unsigned integer from 0 to Max (inclusive).
  87 size_t randomIndex(size_t Max);
  88
  89 // Picks a random bit among the bits set in Vector and returns its index.
  90 // Precondition: Vector must have at least one bit set.
  91 size_t randomBit(const BitVector &Vector);
  92
  93 // Picks a random configuration, then selects a random def and a random use from
  94 // it and finally set the selected values in the provided InstructionInstances.
  95 void setRandomAliasing(const AliasingConfigurations &AliasingConfigurations,
  96                        InstructionTemplate &DefIB, InstructionTemplate &UseIB);
  97
  98 // Assigns a Random Value to all Variables in IT that are still Invalid.
  99 // Do not use any of the registers in `ForbiddenRegs`.
 100 void randomizeUnsetVariables(const ExegesisTarget &Target,
 101                              const BitVector &ForbiddenRegs,
 102                              InstructionTemplate &IT);
 103
 104 } // namespace exegesis
 105 } // namespace llvm
 106
 107 #endif // LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H