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/ADT/CombinationGenerator.h"
25 #include "llvm/MC/MCInst.h"
26 #include "llvm/Support/Error.h"
27 #include <cstdlib>
28 #include <memory>
29 #include <vector>
30 
31 namespace llvm {
32 namespace exegesis {
33 
34 std::vector<CodeTemplate> getSingleton(CodeTemplate &&CT);
35 
36 // Generates code templates that has a self-dependency.
37 Expected<std::vector<CodeTemplate>>
38 generateSelfAliasingCodeTemplates(InstructionTemplate Variant,
39                                   const BitVector &ForbiddenRegisters);
40 
41 // Generates code templates without assignment constraints.
42 Expected<std::vector<CodeTemplate>>
43 generateUnconstrainedCodeTemplates(const InstructionTemplate &Variant,
44                                    StringRef Msg);
45 
46 // A class representing failures that happened during Benchmark, they are used
47 // to report informations to the user.
48 class SnippetGeneratorFailure : public StringError {
49 public:
50   SnippetGeneratorFailure(const Twine &S);
51 };
52 
53 // Common code for all benchmark modes.
54 class SnippetGenerator {
55 public:
56   struct Options {
57     unsigned MaxConfigsPerOpcode = 1;
58   };
59 
60   explicit SnippetGenerator(const LLVMState &State, const Options &Opts);
61 
62   virtual ~SnippetGenerator();
63 
64   // Calls generateCodeTemplate and expands it into one or more BenchmarkCode.
65   Error generateConfigurations(const InstructionTemplate &Variant,
66                                std::vector<BenchmarkCode> &Benchmarks,
67                                const BitVector &ExtraForbiddenRegs) const;
68 
69   // Given a snippet, computes which registers the setup code needs to define.
70   std::vector<RegisterValue> computeRegisterInitialValues(
71       const std::vector<InstructionTemplate> &Snippet) const;
72 
73 protected:
74   const LLVMState &State;
75   const Options Opts;
76 
77 private:
78   // API to be implemented by subclasses.
79   virtual Expected<std::vector<CodeTemplate>>
80   generateCodeTemplates(InstructionTemplate Variant,
81                         const BitVector &ForbiddenRegisters) const = 0;
82 };
83 
84 // A global Random Number Generator to randomize configurations.
85 // FIXME: Move random number generation into an object and make it seedable for
86 // unit tests.
87 std::mt19937 &randomGenerator();
88 
89 // Picks a random unsigned integer from 0 to Max (inclusive).
90 size_t randomIndex(size_t Max);
91 
92 // Picks a random bit among the bits set in Vector and returns its index.
93 // Precondition: Vector must have at least one bit set.
94 size_t randomBit(const BitVector &Vector);
95 
96 // Picks a first bit that is common to these two vectors.
97 std::optional<int> getFirstCommonBit(const BitVector &A, const BitVector &B);
98 
99 // Picks a random configuration, then selects a random def and a random use from
100 // it and finally set the selected values in the provided InstructionInstances.
101 void setRandomAliasing(const AliasingConfigurations &AliasingConfigurations,
102                        InstructionTemplate &DefIB, InstructionTemplate &UseIB);
103 
104 // Assigns a Random Value to all Variables in IT that are still Invalid.
105 // Do not use any of the registers in `ForbiddenRegs`.
106 Error randomizeUnsetVariables(const LLVMState &State,
107                               const BitVector &ForbiddenRegs,
108                               InstructionTemplate &IT);
109 
110 } // namespace exegesis
111 } // namespace llvm
112 
113 #endif // LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
114