231 lines
8.5 KiB
C
231 lines
8.5 KiB
C
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//===-- SnippetGenerator.h --------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// Defines the abstract SnippetGenerator class for generating code that allows
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/// measuring a certain property of instructions (e.g. latency).
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
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#define LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
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#include "Assembler.h"
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#include "BenchmarkCode.h"
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#include "CodeTemplate.h"
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#include "LlvmState.h"
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#include "MCInstrDescView.h"
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#include "RegisterAliasing.h"
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#include "llvm/MC/MCInst.h"
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#include "llvm/Support/Error.h"
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#include <cstdlib>
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#include <memory>
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#include <vector>
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namespace llvm {
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namespace exegesis {
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std::vector<CodeTemplate> getSingleton(CodeTemplate &&CT);
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// Generates code templates that has a self-dependency.
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Expected<std::vector<CodeTemplate>>
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generateSelfAliasingCodeTemplates(InstructionTemplate Variant);
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// Generates code templates without assignment constraints.
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Expected<std::vector<CodeTemplate>>
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generateUnconstrainedCodeTemplates(const InstructionTemplate &Variant,
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StringRef Msg);
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// A class representing failures that happened during Benchmark, they are used
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// to report informations to the user.
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class SnippetGeneratorFailure : public StringError {
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public:
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SnippetGeneratorFailure(const Twine &S);
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};
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// Common code for all benchmark modes.
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class SnippetGenerator {
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public:
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struct Options {
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unsigned MaxConfigsPerOpcode = 1;
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};
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explicit SnippetGenerator(const LLVMState &State, const Options &Opts);
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virtual ~SnippetGenerator();
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// Calls generateCodeTemplate and expands it into one or more BenchmarkCode.
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Error generateConfigurations(const InstructionTemplate &Variant,
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std::vector<BenchmarkCode> &Benchmarks,
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const BitVector &ExtraForbiddenRegs) const;
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// Given a snippet, computes which registers the setup code needs to define.
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std::vector<RegisterValue> computeRegisterInitialValues(
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const std::vector<InstructionTemplate> &Snippet) const;
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protected:
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const LLVMState &State;
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const Options Opts;
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private:
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// API to be implemented by subclasses.
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virtual Expected<std::vector<CodeTemplate>>
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generateCodeTemplates(InstructionTemplate Variant,
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const BitVector &ForbiddenRegisters) const = 0;
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};
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// A global Random Number Generator to randomize configurations.
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// FIXME: Move random number generation into an object and make it seedable for
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// unit tests.
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std::mt19937 &randomGenerator();
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// Picks a random unsigned integer from 0 to Max (inclusive).
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size_t randomIndex(size_t Max);
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// Picks a random bit among the bits set in Vector and returns its index.
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// Precondition: Vector must have at least one bit set.
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size_t randomBit(const BitVector &Vector);
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// Picks a random configuration, then selects a random def and a random use from
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// it and finally set the selected values in the provided InstructionInstances.
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void setRandomAliasing(const AliasingConfigurations &AliasingConfigurations,
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InstructionTemplate &DefIB, InstructionTemplate &UseIB);
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// Assigns a Random Value to all Variables in IT that are still Invalid.
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// Do not use any of the registers in `ForbiddenRegs`.
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Error randomizeUnsetVariables(const LLVMState &State,
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const BitVector &ForbiddenRegs,
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InstructionTemplate &IT);
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// Combination generator.
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//
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// Example: given input {{0, 1}, {2}, {3, 4}} it will produce the following
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// combinations: {0, 2, 3}, {0, 2, 4}, {1, 2, 3}, {1, 2, 4}.
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//
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// It is important to think of input as vector-of-vectors, where the
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// outer vector is the variable space, and inner vector is choice space.
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// The number of choices for each variable can be different.
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//
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// As for implementation, it is useful to think of this as a weird number,
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// where each digit (==variable) may have different base (==number of choices).
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// Thus modelling of 'produce next combination' is exactly analogous to the
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// incrementing of an number - increment lowest digit (pick next choice for the
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// variable), and if it wrapped to the beginning then increment next digit.
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template <typename choice_type, typename choices_storage_type,
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int variable_smallsize>
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class CombinationGenerator {
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template <typename T> struct WrappingIterator {
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using value_type = T;
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const ArrayRef<value_type> Range;
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typename decltype(Range)::const_iterator Position;
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// Rewind the tape, placing the position to again point at the beginning.
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void rewind() { Position = Range.begin(); }
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// Advance position forward, possibly wrapping to the beginning.
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// Returns whether the wrap happened.
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bool operator++() {
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++Position;
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bool Wrapped = Position == Range.end();
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if (Wrapped)
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rewind();
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return Wrapped;
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}
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// Get the value at which we are currently pointing.
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operator const value_type &() const { return *Position; }
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WrappingIterator(ArrayRef<value_type> Range_) : Range(Range_) {
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assert(!Range.empty() && "The range must not be empty.");
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rewind();
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}
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};
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const ArrayRef<choices_storage_type> VariablesChoices;
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void performGeneration(
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const function_ref<bool(ArrayRef<choice_type>)> Callback) const {
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SmallVector<WrappingIterator<choice_type>, variable_smallsize>
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VariablesState;
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// 'increment' of the the whole VariablesState is defined identically to the
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// increment of a number: starting from the least significant element,
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// increment it, and if it wrapped, then propagate that carry by also
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// incrementing next (more significant) element.
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auto IncrementState =
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[](MutableArrayRef<WrappingIterator<choice_type>> VariablesState)
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-> bool {
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for (WrappingIterator<choice_type> &Variable :
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llvm::reverse(VariablesState)) {
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bool Wrapped = ++Variable;
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if (!Wrapped)
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return false; // There you go, next combination is ready.
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// We have carry - increment more significant variable next..
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}
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return true; // MSB variable wrapped, no more unique combinations.
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};
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// Initialize the per-variable state to refer to the possible choices for
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// that variable.
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VariablesState.reserve(VariablesChoices.size());
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for (ArrayRef<choice_type> VC : VariablesChoices)
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VariablesState.emplace_back(VC);
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// Temporary buffer to store each combination before performing Callback.
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SmallVector<choice_type, variable_smallsize> CurrentCombination;
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CurrentCombination.resize(VariablesState.size());
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while (true) {
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// Gather the currently-selected variable choices into a vector.
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for (auto I : llvm::zip(VariablesState, CurrentCombination))
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std::get<1>(I) = std::get<0>(I);
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// And pass the new combination into callback, as intended.
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if (/*Abort=*/Callback(CurrentCombination))
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return;
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// And tick the state to next combination, which will be unique.
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if (IncrementState(VariablesState))
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return; // All combinations produced.
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}
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};
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public:
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CombinationGenerator(ArrayRef<choices_storage_type> VariablesChoices_)
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: VariablesChoices(VariablesChoices_) {
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#ifndef NDEBUG
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assert(!VariablesChoices.empty() && "There should be some variables.");
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llvm::for_each(VariablesChoices, [](ArrayRef<choice_type> VariableChoices) {
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assert(!VariableChoices.empty() &&
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"There must always be some choice, at least a placeholder one.");
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});
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#endif
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}
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// How many combinations can we produce, max?
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// This is at most how many times the callback will be called.
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size_t numCombinations() const {
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size_t NumVariants = 1;
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for (ArrayRef<choice_type> VariableChoices : VariablesChoices)
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NumVariants *= VariableChoices.size();
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assert(NumVariants >= 1 &&
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"We should always end up producing at least one combination");
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return NumVariants;
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}
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// Actually perform exhaustive combination generation.
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// Each result will be passed into the callback.
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void generate(const function_ref<bool(ArrayRef<choice_type>)> Callback) {
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performGeneration(Callback);
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}
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};
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} // namespace exegesis
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} // namespace llvm
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#endif // LLVM_TOOLS_LLVM_EXEGESIS_SNIPPETGENERATOR_H
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