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//===-- Benchmark memory specific tools -------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file complements the `benchmark` header with memory specific tools and
// benchmarking facilities.
#include "LibcBenchmark.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Alignment.h"
#include <cstdint>
#include <random>
namespace llvm {
namespace libc_benchmarks {
// Configuration
struct StudyConfiguration {
// One of 'memcpy', 'memset', 'memcmp'.
// The underlying implementation is always the llvm libc one.
// e.g. 'memcpy' will test '__llvm_libc::memcpy'
std::string Function;
// The number of trials to run for this benchmark.
// If in SweepMode, each individual sizes are measured 'NumTrials' time.
// i.e 'NumTrials' measurements for 0, 'NumTrials' measurements for 1 ...
uint32_t NumTrials = 1;
// Toggles between Sweep Mode and Distribution Mode (default).
// See 'SweepModeMaxSize' and 'SizeDistributionName' below.
bool IsSweepMode = false;
// Maximum size to use when measuring a ramp of size values (SweepMode).
// The benchmark measures all sizes from 0 to SweepModeMaxSize.
// Note: in sweep mode the same size is sampled several times in a row this
// will allow the processor to learn it and optimize the branching pattern.
// The resulting measurement is likely to be idealized.
uint32_t SweepModeMaxSize = 0; // inclusive
// The name of the distribution to be used to randomize the size parameter.
// This is used when SweepMode is false (default).
std::string SizeDistributionName;
// This parameter allows to control how the buffers are accessed during
// benchmark:
// None : Use a fixed address that is at least cache line aligned,
// 1 : Use random address,
// >1 : Use random address aligned to value.
MaybeAlign AccessAlignment = None;
// When Function == 'memcmp', this is the buffers mismatch position.
// 0 : Buffers always compare equal,
// >0 : Buffers compare different at byte N-1.
uint32_t MemcmpMismatchAt = 0;
struct Runtime {
// Details about the Host (cpu name, cpu frequency, cache hierarchy).
HostState Host;
// The framework will populate this value so all data accessed during the
// benchmark will stay in L1 data cache. This includes bookkeeping data.
uint32_t BufferSize = 0;
// This is the number of distinct parameters used in a single batch.
// The framework always tests a batch of randomized parameter to prevent the
// cpu from learning branching patterns.
uint32_t BatchParameterCount = 0;
// The benchmark options that were used to perform the measurement.
// This is decided by the framework.
BenchmarkOptions BenchmarkOptions;
// Results
// The root object containing all the data (configuration and measurements).
struct Study {
std::string StudyName;
Runtime Runtime;
StudyConfiguration Configuration;
std::vector<Duration> Measurements;
// Utils
// Provides an aligned, dynamically allocated buffer.
class AlignedBuffer {
char *const Buffer = nullptr;
size_t Size = 0;
static constexpr size_t Alignment = 1024;
explicit AlignedBuffer(size_t Size)
: Buffer(static_cast<char *>(aligned_alloc(Alignment, Size))),
Size(Size) {}
~AlignedBuffer() { free(Buffer); }
inline char *operator+(size_t Index) { return Buffer + Index; }
inline const char *operator+(size_t Index) const { return Buffer + Index; }
inline char &operator[](size_t Index) { return Buffer[Index]; }
inline const char &operator[](size_t Index) const { return Buffer[Index]; }
inline char *begin() { return Buffer; }
inline char *end() { return Buffer + Size; }
// Helper to generate random buffer offsets that satisfy the configuration
// constraints.
class OffsetDistribution {
std::uniform_int_distribution<uint32_t> Distribution;
uint32_t Factor;
explicit OffsetDistribution(size_t BufferSize, size_t MaxSizeValue,
MaybeAlign AccessAlignment);
template <class Generator> uint32_t operator()(Generator &G) {
return Distribution(G) * Factor;
// Helper to generate random buffer offsets that satisfy the configuration
// constraints. It is specifically designed to benchmark `memcmp` functions
// where we may want the Nth byte to differ.
class MismatchOffsetDistribution {
std::uniform_int_distribution<size_t> MismatchIndexSelector;
llvm::SmallVector<uint32_t, 16> MismatchIndices;
const uint32_t MismatchAt;
explicit MismatchOffsetDistribution(size_t BufferSize, size_t MaxSizeValue,
size_t MismatchAt);
explicit operator bool() const { return !MismatchIndices.empty(); }
const llvm::SmallVectorImpl<uint32_t> &getMismatchIndices() const {
return MismatchIndices;
template <class Generator> uint32_t operator()(Generator &G, uint32_t Size) {
const uint32_t MismatchIndex = MismatchIndices[MismatchIndexSelector(G)];
// We need to position the offset so that a mismatch occurs at MismatchAt.
if (Size >= MismatchAt)
return MismatchIndex - MismatchAt;
// Size is too small to trigger the mismatch.
return MismatchIndex - Size - 1;
} // namespace libc_benchmarks
} // namespace llvm