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

[Louis Dionne via libcxx-commits]

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@@ -39,10 +44,83 @@ __adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
   return __i;
 }
 
+template <class _Iter, class _Sent, class _BinaryPredicate>
+_LIBCPP_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>
+_LIBCPP_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];
+
+      for (size_t __i = 0; __i != __unroll_count; ++__i) {
----------------
ldionne wrote:

It might be useful to add a short comment explaining why you don't test the `__all_of` in this loop: it's to avoid adding an early return and let the compiler do good stuff.

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