vectorize replace 🎭

benchmarks/src/replace.cpp

@@ -37,6 +37,17 @@ const char src[] =
     "euismod eros, ut posuere ligula ullamcorper id. Nullam aliquam malesuada est at dignissim. Pellentesque finibus "
     "sagittis libero nec bibendum. Phasellus dolor ipsum, finibus quis turpis quis, mollis interdum felis.";
 
+template <class T>
+void r(benchmark::State& state) {
+    const std::vector<T> a(std::begin(src), std::end(src));
+    std::vector<T> b(std::size(src));
+
+    for (auto _ : state) {
+        b = a;
+        std::replace(std::begin(b), std::end(b), T{'m'}, T{'w'});
+    }
+}
+
 template <class T>
 void rc(benchmark::State& state) {
     const std::vector<T> a(std::begin(src), std::end(src));
@@ -58,6 +69,10 @@ void rc_if(benchmark::State& state) {
     }
 }
 
+// replace() is vectorized for 4 and 8 bytes only.
+BENCHMARK(r<std::uint32_t>);
+BENCHMARK(r<std::uint64_t>);
+
 BENCHMARK(rc<std::uint8_t>);
 BENCHMARK(rc<std::uint16_t>);
 BENCHMARK(rc<std::uint32_t>);

stl/inc/algorithm

@@ -73,6 +73,12 @@ __declspec(noalias) _Min_max_8i __stdcall __std_minmax_8i(const void* _First, co
 __declspec(noalias) _Min_max_8u __stdcall __std_minmax_8u(const void* _First, const void* _Last) noexcept;
 __declspec(noalias) _Min_max_f __stdcall __std_minmax_f(const void* _First, const void* _Last) noexcept;
 __declspec(noalias) _Min_max_d __stdcall __std_minmax_d(const void* _First, const void* _Last) noexcept;
+
+// TRANSITION, DevCom-10610477
+__declspec(noalias) void __stdcall __std_replace_4(
+    void* _First, void* _Last, uint32_t _Old_val, uint32_t _New_val) noexcept;
+__declspec(noalias) void __stdcall __std_replace_8(
+    void* _First, void* _Last, uint64_t _Old_val, uint64_t _New_val) noexcept;
 } // extern "C"
 
 _STD_BEGIN
@@ -180,6 +186,24 @@ _Ty1* __std_find_first_of_trivial(
     }
 }
 
+template <class _Ty, class _TVal1, class _TVal2>
+__declspec(noalias) void _Replace_vectorized(
+    _Ty* const _First, _Ty* const _Last, const _TVal1 _Old_val, const _TVal2 _New_val) noexcept {
+    if constexpr (is_pointer_v<_Ty>) {
+#ifdef _WIN64
+        ::__std_replace_8(_First, _Last, reinterpret_cast<uint64_t>(_Old_val), reinterpret_cast<uint64_t>(_New_val));
+#else // ^^^ defined(_WIN64) / !defined(_WIN64) vvv
+        ::__std_replace_4(_First, _Last, reinterpret_cast<uint32_t>(_Old_val), reinterpret_cast<uint32_t>(_New_val));
+#endif // ^^^ !defined(_WIN64) ^^^
+    } else if constexpr (sizeof(_Ty) == 4) {
+        ::__std_replace_4(_First, _Last, static_cast<uint32_t>(_Old_val), static_cast<uint32_t>(_New_val));
+    } else if constexpr (sizeof(_Ty) == 8) {
+        ::__std_replace_8(_First, _Last, static_cast<uint64_t>(_Old_val), static_cast<uint64_t>(_New_val));
+    } else {
+        static_assert(_Always_false<_Ty>, "Unexpected size");
+    }
+}
+
 // find_first_of vectorization is likely to be a win after this size (in elements)
 _INLINE_VAR constexpr ptrdiff_t _Threshold_find_first_of = 16;
 
@@ -188,6 +212,17 @@ template <class _It1, class _It2, class _Pr>
 _INLINE_VAR constexpr bool _Vector_alg_in_find_first_of_is_safe =
     _Equal_memcmp_is_safe<_It1, _It2, _Pr> // can replace value comparison with bitwise comparison
     && sizeof(_Iter_value_t<_It1>) <= 2; // pcmpestri compatible size
+
+// Can we activate the vector algorithms for replace?
+template <class _Iter, class _Ty1>
+constexpr bool _Vector_alg_in_replace_is_safe = _Vector_alg_in_find_is_safe<_Iter, _Ty1> // can search for the value
+                                             && sizeof(_Iter_value_t<_Iter>) >= 4; // avx masked op compatible size
+
+// Can we activate the vector algorithms for ranges::replace?
+template <class _Iter, class _Ty1, class _Ty2>
+constexpr bool _Vector_alg_in_ranges_replace_is_safe =
+    _Vector_alg_in_replace_is_safe<_Iter, _Ty1> // can search and replace
+    && _Vector_alg_in_find_is_safe_elem<_Ty2, _Iter_value_t<_Iter>>; // replacement fits
 _STD_END
 #endif // _USE_STD_VECTOR_ALGORITHMS
 
@@ -3807,6 +3842,22 @@ _CONSTEXPR20 void replace(const _FwdIt _First, const _FwdIt _Last, const _Ty& _O
     _STD _Adl_verify_range(_First, _Last);
     auto _UFirst      = _STD _Get_unwrapped(_First);
     const auto _ULast = _STD _Get_unwrapped(_Last);
+
+#if _USE_STD_VECTOR_ALGORITHMS
+    if constexpr (_Vector_alg_in_replace_is_safe<decltype(_UFirst), _Ty>) {
+#if _HAS_CXX20
+        if (!_STD is_constant_evaluated())
+#endif // _HAS_CXX20
+        {
+            if (_STD _Could_compare_equal_to_value_type<decltype(_UFirst)>(_Oldval)) {
+                _STD _Replace_vectorized(_STD _To_address(_UFirst), _STD _To_address(_ULast), _Oldval, _Newval);
+            }
+
+            return;
+        }
+    }
+#endif // _USE_STD_VECTOR_ALGORITHMS
+
     for (; _UFirst != _ULast; ++_UFirst) {
         if (*_UFirst == _Oldval) {
             *_UFirst = _Newval;
@@ -3860,6 +3911,23 @@ namespace ranges {
             _STL_INTERNAL_STATIC_ASSERT(indirectly_writable<_It, const _Ty2&>);
             _STL_INTERNAL_STATIC_ASSERT(indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty1*>);
 
+#if _USE_STD_VECTOR_ALGORITHMS
+            if constexpr (is_same_v<_Pj, identity> && sized_sentinel_for<_Se, _It>
+                          && _Vector_alg_in_ranges_replace_is_safe<_It, _Ty1, _Ty2>) {
+                if (!_STD is_constant_evaluated()) {
+                    const auto _Count = _Last - _First;
+
+                    if (_STD _Could_compare_equal_to_value_type<_It>(_Oldval)) {
+                        const auto _First_ptr = _STD to_address(_First);
+                        const auto _Last_ptr  = _First_ptr + _Count;
+                        _STD _Replace_vectorized(_First_ptr, _Last_ptr, _Oldval, _Newval);
+                    }
+
+                    return _First + _Count;
+                }
+            }
+#endif // _USE_STD_VECTOR_ALGORITHMS
+
             for (; _First != _Last; ++_First) {
                 if (_STD invoke(_Proj, *_First) == _Oldval) {
                     *_First = _Newval;

stl/inc/xutility

@@ -5830,30 +5830,34 @@ struct _Vector_alg_in_find_is_safe_object_pointers<_Ty1*, _Ty2*>
           // either _Ty1 is the same as _Ty2 (ignoring cv-qualifiers), or one of the two is void
           disjunction<is_same<remove_cv_t<_Ty1>, remove_cv_t<_Ty2>>, is_void<_Ty1>, is_void<_Ty2>>> {};
 
+// Can we activate the vector algorithms to find a value in a range of elements?
+template <class _Ty, class _Elem>
+constexpr bool _Vector_alg_in_find_is_safe_elem = disjunction_v<
+#ifdef __cpp_lib_byte
+    // We're finding a std::byte in a range of std::byte.
+    conjunction<is_same<_Ty, byte>, is_same<_Elem, byte>>,
+#endif // defined(__cpp_lib_byte)
+    // We're finding an integer in a range of integers.
+    // This case is the one that requires careful runtime handling in _Could_compare_equal_to_value_type.
+    conjunction<is_integral<_Ty>, is_integral<_Elem>>,
+    // We're finding an (object or function) pointer in a range of pointers of the same type.
+    conjunction<is_pointer<_Ty>, is_same<_Ty, _Elem>>,
+    // We're finding a nullptr in a range of (object or function) pointers.
+    conjunction<is_same<_Ty, nullptr_t>, is_pointer<_Elem>>,
+    // We're finding an object pointer in a range of object pointers, and:
+    // - One of the pointer types is a cv void*.
+    // - One of the pointer types is a cv1 U* and the other is a cv2 U*.
+    _Vector_alg_in_find_is_safe_object_pointers<_Ty, _Elem>>;
+
 // Can we activate the vector algorithms for find/count?
-template <class _Iter, class _Ty, class _Elem = _Iter_value_t<_Iter>>
-_INLINE_VAR constexpr bool _Vector_alg_in_find_is_safe =
+template <class _Iter, class _Ty>
+constexpr bool _Vector_alg_in_find_is_safe =
     // The iterator must be contiguous so we can get raw pointers.
     _Iterator_is_contiguous<_Iter>
     // The iterator must not be volatile.
     && !_Iterator_is_volatile<_Iter>
-    // And one of the following conditions must be met:
-    && disjunction_v<
-#ifdef __cpp_lib_byte
-        // We're finding a std::byte in a range of std::byte.
-        conjunction<is_same<_Ty, byte>, is_same<_Elem, byte>>,
-#endif // defined(__cpp_lib_byte)
-       // We're finding an integer in a range of integers.
-       // This case is the one that requires careful runtime handling in _Could_compare_equal_to_value_type.
-        conjunction<is_integral<_Ty>, is_integral<_Elem>>,
-        // We're finding an (object or function) pointer in a range of pointers of the same type.
-        conjunction<is_pointer<_Ty>, is_same<_Ty, _Elem>>,
-        // We're finding a nullptr in a range of (object or function) pointers.
-        conjunction<is_same<_Ty, nullptr_t>, is_pointer<_Elem>>,
-        // We're finding an object pointer in a range of object pointers, and:
-        // - One of the pointer types is a cv void*.
-        // - One of the pointer types is a cv1 U* and the other is a cv2 U*.
-        _Vector_alg_in_find_is_safe_object_pointers<_Ty, _Elem>>;
+    // The type of the value to find must be compatible with the type of the elements.
+    && _Vector_alg_in_find_is_safe_elem<_Ty, _Iter_value_t<_Iter>>;
 
 template <class _InIt, class _Ty>
 _NODISCARD constexpr bool _Could_compare_equal_to_value_type(const _Ty& _Val) {

stl/src/vector_algorithms.cpp

@@ -2272,6 +2272,83 @@ __declspec(noalias) size_t
     return __std_mismatch_impl<_Find_traits_8, uint64_t>(_First1, _First2, _Count);
 }
 
+__declspec(noalias) void __stdcall __std_replace_4(
+    void* _First, void* const _Last, const uint32_t _Old_val, const uint32_t _New_val) noexcept {
+#ifndef _M_ARM64EC
+    if (_Use_avx2()) {
+        const __m256i _Comparand   = _mm256_broadcastd_epi32(_mm_cvtsi32_si128(_Old_val));
+        const __m256i _Replacement = _mm256_broadcastd_epi32(_mm_cvtsi32_si128(_New_val));
+        const size_t _Full_length  = _Byte_length(_First, _Last);
+
+        void* _Stop_at = _First;
+        _Advance_bytes(_Stop_at, _Full_length & ~size_t{0x1F});
+
+        while (_First != _Stop_at) {
+            const __m256i _Data = _mm256_loadu_si256(reinterpret_cast<const __m256i*>(_First));
+            const __m256i _Mask = _mm256_cmpeq_epi32(_Comparand, _Data);
+            _mm256_maskstore_epi32(reinterpret_cast<int*>(_First), _Mask, _Replacement);
+
+            _Advance_bytes(_First, 32);
+        }
+
+        if (const size_t _Tail_length = _Full_length & 0x1C; _Tail_length != 0) {
+            const __m256i _Tail_mask = _Avx2_tail_mask_32(_Tail_length >> 2);
+            const __m256i _Data      = _mm256_maskload_epi32(reinterpret_cast<const int*>(_First), _Tail_mask);
+            const __m256i _Mask      = _mm256_and_si256(_mm256_cmpeq_epi32(_Comparand, _Data), _Tail_mask);
+            _mm256_maskstore_epi32(reinterpret_cast<int*>(_First), _Mask, _Replacement);
+        }
+    } else
+#endif // !defined(_M_ARM64EC)
+    {
+        for (auto _Cur = reinterpret_cast<uint32_t*>(_First); _Cur != _Last; ++_Cur) {
+            if (*_Cur == _Old_val) {
+                *_Cur = _New_val;
+            }
+        }
+    }
+}
+
+__declspec(noalias) void __stdcall __std_replace_8(
+    void* _First, void* const _Last, const uint64_t _Old_val, const uint64_t _New_val) noexcept {
+#ifndef _M_ARM64EC
+    if (_Use_avx2()) {
+#ifdef _WIN64
+        const __m256i _Comparand   = _mm256_broadcastq_epi64(_mm_cvtsi64_si128(_Old_val));
+        const __m256i _Replacement = _mm256_broadcastq_epi64(_mm_cvtsi64_si128(_New_val));
+#else // ^^^ defined(_WIN64) / !defined(_WIN64), workaround, _mm_cvtsi64_si128 does not compile vvv
+        const __m256i _Comparand   = _mm256_set1_epi64x(_Old_val);
+        const __m256i _Replacement = _mm256_set1_epi64x(_New_val);
+#endif // ^^^ !defined(_WIN64) ^^^
+        const size_t _Full_length = _Byte_length(_First, _Last);
+
+        void* _Stop_at = _First;
+        _Advance_bytes(_Stop_at, _Full_length & ~size_t{0x1F});
+
+        while (_First != _Stop_at) {
+            const __m256i _Data = _mm256_loadu_si256(reinterpret_cast<const __m256i*>(_First));
+            const __m256i _Mask = _mm256_cmpeq_epi64(_Comparand, _Data);
+            _mm256_maskstore_epi64(reinterpret_cast<long long*>(_First), _Mask, _Replacement);
+
+            _Advance_bytes(_First, 32);
+        }
+
+        if (const size_t _Tail_length = _Full_length & 0x18; _Tail_length != 0) {
+            const __m256i _Tail_mask = _Avx2_tail_mask_32(_Tail_length >> 2);
+            const __m256i _Data      = _mm256_maskload_epi64(reinterpret_cast<const long long*>(_First), _Tail_mask);
+            const __m256i _Mask      = _mm256_and_si256(_mm256_cmpeq_epi64(_Comparand, _Data), _Tail_mask);
+            _mm256_maskstore_epi64(reinterpret_cast<long long*>(_First), _Mask, _Replacement);
+        }
+    } else
+#endif // !defined(_M_ARM64EC)
+    {
+        for (auto _Cur = reinterpret_cast<uint64_t*>(_First); _Cur != _Last; ++_Cur) {
+            if (*_Cur == _Old_val) {
+                *_Cur = _New_val;
+            }
+        }
+    }
+}
+
 } // extern "C"
 
 #ifndef _M_ARM64EC

tests/std/tests/VSO_0000000_vector_algorithms/test.cpp

@@ -536,6 +536,52 @@ namespace test_mismatch_sizes_and_alignments {
     }
 } // namespace test_mismatch_sizes_and_alignments
 
+template <class FwdIt, class T>
+void last_known_good_replace(FwdIt first, FwdIt last, const T old_val, const T new_val) {
+    for (; first != last; ++first) {
+        if (*first == old_val) {
+            *first = new_val;
+        }
+    }
+}
+
+template <class T>
+void test_case_replace(const vector<T>& input, T old_val, T new_val) {
+    vector<T> replaced_actual(input);
+    vector<T> replaced_expected(input);
+    replace(replaced_actual.begin(), replaced_actual.end(), old_val, new_val);
+    last_known_good_replace(replaced_expected.begin(), replaced_expected.end(), old_val, new_val);
+    assert(replaced_expected == replaced_actual);
+
+#if _HAS_CXX20
+    vector<T> replaced_actual_r(input);
+    ranges::replace(replaced_actual_r, old_val, new_val);
+    assert(replaced_expected == replaced_actual_r);
+#endif // _HAS_CXX20
+}
+
+template <class T>
+void test_replace(mt19937_64& gen) {
+    using TD = conditional_t<sizeof(T) == 1, int, T>;
+    uniform_int_distribution<TD> dis(0, 9);
+    vector<T> input;
+
+    input.reserve(dataCount);
+
+    {
+        const T old_val = static_cast<T>(dis(gen));
+        const T new_val = static_cast<T>(dis(gen));
+        test_case_replace(input, old_val, new_val);
+    }
+
+    for (size_t i = 0; i != dataCount; ++i) {
+        input.push_back(static_cast<T>(dis(gen)));
+        const T old_val = static_cast<T>(dis(gen));
+        const T new_val = static_cast<T>(dis(gen));
+        test_case_replace(input, old_val, new_val);
+    }
+}
+
 template <class BidIt>
 void last_known_good_reverse(BidIt first, BidIt last) {
     for (; first != last && first != --last; ++first) {
@@ -728,6 +774,12 @@ void test_vector_algorithms(mt19937_64& gen) {
     test_mismatch_sizes_and_alignments::test<int>();
     test_mismatch_sizes_and_alignments::test<long long>();
 
+    // replace() is vectorized for 4 and 8 bytes only.
+    test_replace<int>(gen);
+    test_replace<unsigned int>(gen);
+    test_replace<long long>(gen);
+    test_replace<unsigned long long>(gen);
+
     test_reverse<char>(gen);
     test_reverse<signed char>(gen);
     test_reverse<unsigned char>(gen);