[libcxx-commits] [libcxx] [libc++] Vectorize std::adjacent_find (PR #89757)

[Louis Dionne via libcxx-commits]

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@@ -39,10 +44,84 @@ __adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
   return __i;
 }
 
+template <class _Iter, class _Sent, class _BinaryPredicate>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Iter
+__adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
+  return std::__adjacent_find_loop(__first, __last, __pred);
+}
+
+#if _LIBCPP_VECTORIZE_ALGORITHMS
+
+template <class _Tp, class _Pred>
+[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp*
+__adjacent_find_vectorized(_Tp* __first, _Tp* __last, _Pred& __pred) {
+  constexpr size_t __unroll_count = 4;
+  constexpr size_t __vec_size     = __native_vector_size<_Tp>;
+  using __vec                     = __simd_vector<_Tp, __vec_size>;
+
+  if (!__libcpp_is_constant_evaluated()) {
+    auto __orig_first = __first;
+    while (static_cast<size_t>(__last - __first) > __unroll_count * __vec_size) [[__unlikely__]] {
+      __vec __cmp_res[__unroll_count];
+
+      // Store the comparison results first to make sure the compiler is allowed to reorder any loads.
+      for (size_t __i = 0; __i != __unroll_count; ++__i) {
+        __cmp_res[__i] = std::__load_vector<__vec>(__first + __i * __vec_size) !=
+                         std::__load_vector<__vec>(__first + __i * __vec_size + 1);
+      }
+
+      for (size_t __i = 0; __i != __unroll_count; ++__i) {
+        if (!std::__all_of(__cmp_res[__i])) {
+          auto __offset = __i * __vec_size + std::__find_first_not_set(__cmp_res[__i]);
+          return __first + __offset;
+        }
+      }
+
+      __first += __unroll_count * __vec_size;
+    }
+
+    // check the last 0-3 vectors
+    while (static_cast<size_t>(__last - __first) > __vec_size) [[__unlikely__]] {
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ldionne wrote:

Same comment about a `for` loop.

https://github.com/llvm/llvm-project/pull/89757