| //===-- Implementation of memcpy ------------------------------------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "src/string/memcpy.h" |
| #include "src/__support/common.h" |
| #include "src/string/memory_utils/elements.h" |
| |
| namespace __llvm_libc { |
| |
| // Whether to use only rep;movsb. |
| constexpr bool kUseOnlyRepMovsb = |
| LLVM_LIBC_IS_DEFINED(LLVM_LIBC_MEMCPY_X86_USE_ONLY_REPMOVSB); |
| |
| // kRepMovsBSize == -1 : Only CopyAligned is used. |
| // kRepMovsBSize == 0 : Only RepMovsb is used. |
| // else CopyAligned is used up to kRepMovsBSize and then RepMovsb. |
| constexpr size_t kRepMovsBSize = |
| #ifdef LLVM_LIBC_MEMCPY_X86_USE_REPMOVSB_FROM_SIZE |
| LLVM_LIBC_MEMCPY_X86_USE_REPMOVSB_FROM_SIZE; |
| #else |
| -1; |
| #endif // LLVM_LIBC_MEMCPY_X86_USE_REPMOVSB_FROM_SIZE |
| |
| // Whether target supports AVX instructions. |
| constexpr bool kHasAvx = LLVM_LIBC_IS_DEFINED(__AVX__); |
| |
| #ifdef __AVX__ |
| using LoopBlockSize = __llvm_libc::x86::_64; |
| #else |
| using LoopBlockSize = __llvm_libc::x86::_32; |
| #endif |
| |
| static void CopyRepMovsb(char *__restrict dst, const char *__restrict src, |
| size_t count) { |
| // FIXME: Add MSVC support with |
| // #include <intrin.h> |
| // __movsb(reinterpret_cast<unsigned char *>(dst), |
| // reinterpret_cast<const unsigned char *>(src), count); |
| asm volatile("rep movsb" : "+D"(dst), "+S"(src), "+c"(count) : : "memory"); |
| } |
| |
| // Design rationale |
| // ================ |
| // |
| // Using a profiler to observe size distributions for calls into libc |
| // functions, it was found most operations act on a small number of bytes. |
| // This makes it important to favor small sizes. |
| // |
| // The tests for `count` are in ascending order so the cost of branching is |
| // proportional to the cost of copying. |
| // |
| // The function is written in C++ for several reasons: |
| // - The compiler can __see__ the code, this is useful when performing Profile |
| // Guided Optimization as the optimized code can take advantage of branching |
| // probabilities. |
| // - It also allows for easier customization and favors testing multiple |
| // implementation parameters. |
| // - As compilers and processors get better, the generated code is improved |
| // with little change on the code side. |
| static void memcpy_x86(char *__restrict dst, const char *__restrict src, |
| size_t count) { |
| // Use x86 strategies (_1, _2, _3 ...) |
| using namespace __llvm_libc::x86; |
| |
| if (kUseOnlyRepMovsb) |
| return CopyRepMovsb(dst, src, count); |
| |
| if (count == 0) |
| return; |
| if (count == 1) |
| return Copy<_1>(dst, src); |
| if (count == 2) |
| return Copy<_2>(dst, src); |
| if (count == 3) |
| return Copy<_3>(dst, src); |
| if (count == 4) |
| return Copy<_4>(dst, src); |
| if (count < 8) |
| return Copy<HeadTail<_4>>(dst, src, count); |
| if (count < 16) |
| return Copy<HeadTail<_8>>(dst, src, count); |
| if (count < 32) |
| return Copy<HeadTail<_16>>(dst, src, count); |
| if (count < 64) |
| return Copy<HeadTail<_32>>(dst, src, count); |
| if (count < 128) |
| return Copy<HeadTail<_64>>(dst, src, count); |
| if (kHasAvx && count < 256) |
| return Copy<HeadTail<_128>>(dst, src, count); |
| if (count <= kRepMovsBSize) |
| return Copy<Align<_32, Arg::Dst>::Then<Loop<LoopBlockSize>>>(dst, src, |
| count); |
| return CopyRepMovsb(dst, src, count); |
| } |
| |
| LLVM_LIBC_FUNCTION(void *, memcpy, |
| (void *__restrict dst, const void *__restrict src, |
| size_t size)) { |
| memcpy_x86(reinterpret_cast<char *>(dst), reinterpret_cast<const char *>(src), |
| size); |
| return dst; |
| } |
| |
| } // namespace __llvm_libc |