[libcxx-commits] [libcxx] [libc++] Start implementing std::datapar::simd (PR #139919)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,165 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___SIMD_ABI_H
+#define _LIBCPP___SIMD_ABI_H
+
+#include <__concepts/convertible_to.h>
+#include <__concepts/equality_comparable.h>
+#include <__config>
+#include <__cstddef/size_t.h>
+#include <__type_traits/standard_types.h>
+#include <__utility/integer_sequence.h>
+#include <cstdint>
+
+#if _LIBCPP_STD_VER >= 26
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+namespace datapar {
+
+template <class _Tp>
+inline constexpr bool __is_vectorizable_type_v = __is_standard_integer_type_v<_Tp> || __is_character_type_v<_Tp>;
+
+template <>
+inline constexpr bool __is_vectorizable_type_v<float> = true;
+
+template <>
+inline constexpr bool __is_vectorizable_type_v<double> = true;
+
+template <class _From, class _To>
+concept __value_preserving_convertible = requires(_From __from) { _To{__from}; };
+
+template <class _Tp>
+concept __constexpr_wrapper_like =
+    convertible_to<_Tp, decltype(_Tp::value)> && equality_comparable_with<_Tp, decltype(_Tp::value)> &&
+    bool_constant<_Tp() == _Tp::value>::value &&
+    bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
+
+// [simd.expos]
+using __simd_size_type = int;
+
+template <class _Tp>
+struct __deduce_abi;
+
+template <class _Tp, __simd_size_type _Np>
+  requires __is_vectorizable_type_v<_Tp> && (_Np <= 64)
----------------
ldionne wrote:

I think this 64 value should be a `static constexpr` with at least a comment explaining why we chose that value over something else. It also needs to be documented in the documentation for implementation-defined values.

If the rationale is as simple as "this is for MSVC compatibility", that's fine.

https://github.com/llvm/llvm-project/pull/139919