[libc++] Vectorize std::find

libcxx/docs/ReleaseNotes/22.rst

@@ -64,6 +64,8 @@ Improvements and New Features
 - Multiple internal types have been refactored to use ``[[no_unique_address]]``, resulting in faster compile times and
   reduced debug information.
 
+- The performance of ``std::find`` has been improved by up to 2x for integral types
+
 Deprecations and Removals
 -------------------------
 

libcxx/include/__algorithm/find.h

@@ -12,6 +12,7 @@
 
 #include <__algorithm/find_segment_if.h>
 #include <__algorithm/min.h>
+#include <__algorithm/simd_utils.h>
 #include <__algorithm/unwrap_iter.h>
 #include <__bit/countr.h>
 #include <__bit/invert_if.h>
@@ -44,39 +45,102 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // generic implementation
 template <class _Iter, class _Sent, class _Tp, class _Proj>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iter
-__find(_Iter __first, _Sent __last, const _Tp& __value, _Proj& __proj) {
+__find_loop(_Iter __first, _Sent __last, const _Tp& __value, _Proj& __proj) {
   for (; __first != __last; ++__first)
     if (std::__invoke(__proj, *__first) == __value)
       break;
   return __first;
 }
 
-// trivially equality comparable implementations
-template <class _Tp,
-          class _Up,
-          class _Proj,
-          __enable_if_t<__is_identity<_Proj>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value &&
-                            sizeof(_Tp) == 1,
-                        int> = 0>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __find(_Tp* __first, _Tp* __last, const _Up& __value, _Proj&) {
-  if (auto __ret = std::__constexpr_memchr(__first, __value, __last - __first))
-    return __ret;
-  return __last;
+template <class _Iter, class _Sent, class _Tp, class _Proj>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iter
+__find(_Iter __first, _Sent __last, const _Tp& __value, _Proj& __proj) {
+  return std::__find_loop(std::move(__first), std::move(__last), __value, __proj);
 }
 
-#if _LIBCPP_HAS_WIDE_CHARACTERS
-template <class _Tp,
-          class _Up,
-          class _Proj,
-          __enable_if_t<__is_identity<_Proj>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value &&
-                            sizeof(_Tp) == sizeof(wchar_t) && _LIBCPP_ALIGNOF(_Tp) >= _LIBCPP_ALIGNOF(wchar_t),
-                        int> = 0>
+#if _LIBCPP_VECTORIZE_ALGORITHMS
+template <class _Tp, class _Up>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __find_vectorized(_Tp* __first, _Tp* __last, _Up __value) {
+  if (!__libcpp_is_constant_evaluated()) {
+    constexpr size_t __unroll_count = 4;
+    constexpr size_t __vec_size     = __native_vector_size<_Tp>;
+    using __vec                     = __simd_vector<_Tp, __vec_size>;
+
+    auto __orig_first = __first;
+
+    auto __values = static_cast<__simd_vector<_Up, __vec_size>>(__value); // broadcast the value
+    while (static_cast<size_t>(__last - __first) >= __unroll_count * __vec_size) [[__unlikely__]] {
+      __vec __lhs[__unroll_count];
+
+      for (size_t __i = 0; __i != __unroll_count; ++__i)
+        __lhs[__i] = std::__load_vector<__vec>(__first + __i * __vec_size);
+
+      for (size_t __i = 0; __i != __unroll_count; ++__i) {
+        if (auto __cmp_res = __lhs[__i] == __values; std::__any_of(__cmp_res)) {
+          auto __offset = __i * __vec_size + std::__find_first_set(__cmp_res);
+          return __first + __offset;
+        }
+      }
+
+      __first += __unroll_count * __vec_size;
+    }
+
+    // check the remaining 0-3 vectors
+    while (static_cast<size_t>(__last - __first) >= __vec_size) {
+      if (auto __cmp_res = std::__load_vector<__vec>(__first) == __values; std::__any_of(__cmp_res)) {
+        return __first + std::__find_first_set(__cmp_res);
+      }
+      __first += __vec_size;
+    }
+
+    if (__last - __first == 0)
+      return __first;
+
+    // Check if we can load elements in front of the current pointer. If that's the case load a vector at
+    // (last - vector_size) to check the remaining elements
+    if (static_cast<size_t>(__first - __orig_first) >= __vec_size) {
+      __first = __last - __vec_size;
+      return __first + std::__find_first_set(std::__load_vector<__vec>(__first) == __values);
+    }
+  }
+
+  __identity __proj;
+  return std::__find_loop(__first, __last, __value, __proj);
+}
+#endif
+
+#ifndef _LIBCPP_CXX03_LANG
+// trivially equality comparable implementations
+template <
+    class _Tp,
+    class _Up,
+    class _Proj,
+    __enable_if_t<__is_identity<_Proj>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __find(_Tp* __first, _Tp* __last, const _Up& __value, _Proj&) {
-  if (auto __ret = std::__constexpr_wmemchr(__first, __value, __last - __first))
-    return __ret;
-  return __last;
+  if constexpr (sizeof(_Tp) == 1) {
+    if (auto __ret = std::__constexpr_memchr(__first, __value, __last - __first))
+      return __ret;
+    return __last;
+  }
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+  else if constexpr (sizeof(_Tp) == sizeof(wchar_t) && _LIBCPP_ALIGNOF(_Tp) >= _LIBCPP_ALIGNOF(wchar_t)) {
+    if (auto __ret = std::__constexpr_wmemchr(__first, __value, __last - __first))
+      return __ret;
+    return __last;
+  }
+#  endif
+#  if _LIBCPP_VECTORIZE_ALGORITHMS
+  else if constexpr (is_integral<_Tp>::value) {
+    return std::__find_vectorized(__first, __last, __value);
+  }
+#  endif
+  else {
+    __identity __proj;
+    return std::__find_loop(__first, __last, __value, __proj);
+  }
 }
-#endif // _LIBCPP_HAS_WIDE_CHARACTERS
+#endif
 
 // TODO: This should also be possible to get right with different signedness
 // cast integral types to allow vectorization

libcxx/include/__algorithm/simd_utils.h

@@ -114,6 +114,11 @@ template <class _VecT, class _Iter>
   }(make_index_sequence<__simd_vector_size_v<_VecT>>{});
 }
 
+template <class _Tp, size_t _Np>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool __any_of(__simd_vector<_Tp, _Np> __vec) noexcept {
+  return __builtin_reduce_or(__builtin_convertvector(__vec, __simd_vector<bool, _Np>));
+}
+
 template <class _Tp, size_t _Np>
 [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool __all_of(__simd_vector<_Tp, _Np> __vec) noexcept {
   return __builtin_reduce_and(__builtin_convertvector(__vec, __simd_vector<bool, _Np>));

libcxx/include/module.modulemap.in

@@ -1225,6 +1225,7 @@ module std [system] {
     header "deque"
     export *
     export std.iterator.reverse_iterator
+    export std.algorithm.simd_utils // This is a workaround for https://llvm.org/PR120108.
   }
 
   module exception {
@@ -2238,6 +2239,7 @@ module std [system] {
     header "vector"
     export std.iterator.reverse_iterator
     export *
+    export std.algorithm.simd_utils // This is a workaround for https://llvm.org/PR120108.
   }
 
   // Experimental C++ Standard Library interfaces

libcxx/test/benchmarks/algorithms/nonmodifying/find.bench.cpp

@@ -51,6 +51,7 @@ int main(int argc, char** argv) {
     // find
     bm.template operator()<std::vector<char>>("std::find(vector<char>) (" + comment + ")", std_find);
     bm.template operator()<std::vector<int>>("std::find(vector<int>) (" + comment + ")", std_find);
+    bm.template operator()<std::vector<long long>>("std::find(vector<long long>) (" + comment + ")", std_find);
     bm.template operator()<std::deque<int>>("std::find(deque<int>) (" + comment + ")", std_find);
     bm.template operator()<std::list<int>>("std::find(list<int>) (" + comment + ")", std_find);