From 1603f99a37c5b179a21dbb8000c39a471a950927 Mon Sep 17 00:00:00 2001 From: Nikolas Klauser Date: Tue, 17 Sep 2024 12:04:54 +0200 Subject: [PATCH] [libc++] Explicitly convert to masks in SIMD code (#107983) This makes it clearer when we use masks and avoids MSan complaining. --- libcxx/include/__algorithm/mismatch.h | 8 +-- libcxx/include/__algorithm/simd_utils.h | 77 ++++++++++++++++--------- 2 files changed, 54 insertions(+), 31 deletions(-) diff --git a/libcxx/include/__algorithm/mismatch.h b/libcxx/include/__algorithm/mismatch.h index cb83347584b1a5..006ddbd80c306b 100644 --- a/libcxx/include/__algorithm/mismatch.h +++ b/libcxx/include/__algorithm/mismatch.h @@ -79,7 +79,7 @@ __mismatch_vectorized(_Iter __first1, _Iter __last1, _Iter __first2) { } for (size_t __i = 0; __i != __unroll_count; ++__i) { - if (auto __cmp_res = __lhs[__i] == __rhs[__i]; !std::__all_of(__cmp_res)) { + if (auto __cmp_res = std::__as_mask(__lhs[__i] == __rhs[__i]); !std::__all_of(__cmp_res)) { auto __offset = __i * __vec_size + std::__find_first_not_set(__cmp_res); return {__first1 + __offset, __first2 + __offset}; } @@ -91,7 +91,7 @@ __mismatch_vectorized(_Iter __first1, _Iter __last1, _Iter __first2) { // check the remaining 0-3 vectors while (static_cast(__last1 - __first1) >= __vec_size) { - if (auto __cmp_res = std::__load_vector<__vec>(__first1) == std::__load_vector<__vec>(__first2); + if (auto __cmp_res = std::__as_mask(std::__load_vector<__vec>(__first1) == std::__load_vector<__vec>(__first2)); !std::__all_of(__cmp_res)) { auto __offset = std::__find_first_not_set(__cmp_res); return {__first1 + __offset, __first2 + __offset}; @@ -108,8 +108,8 @@ __mismatch_vectorized(_Iter __first1, _Iter __last1, _Iter __first2) { if (static_cast(__first1 - __orig_first1) >= __vec_size) { __first1 = __last1 - __vec_size; __first2 = __last2 - __vec_size; - auto __offset = - std::__find_first_not_set(std::__load_vector<__vec>(__first1) == std::__load_vector<__vec>(__first2)); + auto __offset = std::__find_first_not_set( + std::__as_mask(std::__load_vector<__vec>(__first1) == std::__load_vector<__vec>(__first2))); return {__first1 + __offset, __first2 + __offset}; } // else loop over the elements individually } diff --git a/libcxx/include/__algorithm/simd_utils.h b/libcxx/include/__algorithm/simd_utils.h index 56518dafa3193b..ec9840f60d87c0 100644 --- a/libcxx/include/__algorithm/simd_utils.h +++ b/libcxx/include/__algorithm/simd_utils.h @@ -116,42 +116,65 @@ template }(make_index_sequence<__simd_vector_size_v<_VecT>>{}); } -template -[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool __all_of(__simd_vector<_Tp, _Np> __vec) noexcept { - return __builtin_reduce_and(__builtin_convertvector(__vec, __simd_vector)); +template +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool __all_of(__simd_vector __vec) noexcept { + return __builtin_reduce_and(__vec); } template -[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_set(__simd_vector<_Tp, _Np> __vec) noexcept { - using __mask_vec = __simd_vector; +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI auto __as_mask(__simd_vector<_Tp, _Np> __vec) noexcept { + static_assert(!is_same<_Tp, bool>::value, "vector type should not be a bool!"); + return __builtin_convertvector(__vec, __simd_vector); +} - // This has MSan disabled du to https://github.com/llvm/llvm-project/issues/85876 - auto __impl = [&](_MaskT) _LIBCPP_NO_SANITIZE("memory") noexcept { -# if defined(_LIBCPP_BIG_ENDIAN) - return std::min( - _Np, std::__countl_zero(__builtin_bit_cast(_MaskT, __builtin_convertvector(__vec, __mask_vec)))); -# else - return std::min( - _Np, std::__countr_zero(__builtin_bit_cast(_MaskT, __builtin_convertvector(__vec, __mask_vec)))); -# endif - }; - - if constexpr (sizeof(__mask_vec) == sizeof(uint8_t)) { - return __impl(uint8_t{}); - } else if constexpr (sizeof(__mask_vec) == sizeof(uint16_t)) { - return __impl(uint16_t{}); - } else if constexpr (sizeof(__mask_vec) == sizeof(uint32_t)) { - return __impl(uint32_t{}); - } else if constexpr (sizeof(__mask_vec) == sizeof(uint64_t)) { - return __impl(uint64_t{}); +// This uses __builtin_convertvector around the __builtin_shufflevector to work around #107981. +template +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI __simd_vector +__extend_vector(__simd_vector __vec) noexcept { + using _VecT = __simd_vector; + if constexpr (_Np == 4) { + return __builtin_convertvector( + __builtin_shufflevector(__vec, _VecT{}, 0, 1, 2, 3, 4, 5, 6, 7), __simd_vector); + } else if constexpr (_Np == 2) { + return std::__extend_vector( + __builtin_convertvector(__builtin_shufflevector(__vec, _VecT{}, 0, 1, 2, 3), __simd_vector)); + } else if constexpr (_Np == 1) { + return std::__extend_vector( + __builtin_convertvector(__builtin_shufflevector(__vec, _VecT{}, 0, 1), __simd_vector)); } else { - static_assert(sizeof(__mask_vec) == 0, "unexpected required size for mask integer type"); + static_assert(sizeof(_VecT) == 0, "Unexpected vector size"); + } +} + +template +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI auto __to_int_mask(__simd_vector __vec) { + if constexpr (_Np < 8) { + return std::__bit_cast(std::__extend_vector(__vec)); + } else if constexpr (_Np == 8) { + return std::__bit_cast(__vec); + } else if constexpr (_Np == 16) { + return std::__bit_cast(__vec); + } else if constexpr (_Np == 32) { + return std::__bit_cast(__vec); + } else if constexpr (_Np == 64) { + return std::__bit_cast(__vec); + } else { + static_assert(sizeof(__simd_vector) == 0, "Unexpected vector size"); return 0; } } -template -[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_not_set(__simd_vector<_Tp, _Np> __vec) noexcept { +template +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_set(__simd_vector __vec) noexcept { +# if defined(_LIBCPP_BIG_ENDIAN) + return std::min(_Np, std::__countl_zero(std::__to_int_mask(__vec))); +# else + return std::min(_Np, std::__countr_zero(std::__to_int_mask(__vec))); +# endif +} + +template +[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t __find_first_not_set(__simd_vector __vec) noexcept { return std::__find_first_set(~__vec); }