add support for [[msvc::intrinsic]] (microsoft#3182)

cdacamar · CaseyCarter · web-flow · commit 48eb4a438cf5 · 2022-10-26T19:28:52.000-07:00
Co-authored-by: Casey Carter &lt;Casey@Carter.net&gt;
diff --git a/stl/inc/type_traits b/stl/inc/type_traits
@@ -1423,26 +1423,25 @@ template <class _Type, template <class...> class _Template>
 struct _Is_specialization : bool_constant<_Is_specialization_v<_Type, _Template>> {};
 
 _EXPORT_STD template <class _Ty>
-_NODISCARD constexpr _Ty&& forward(
-    remove_reference_t<_Ty>& _Arg) noexcept { // forward an lvalue as either an lvalue or an rvalue
+_NODISCARD _MSVC_INTRINSIC constexpr _Ty&& forward(remove_reference_t<_Ty>& _Arg) noexcept {
     return static_cast<_Ty&&>(_Arg);
 }
 
 _EXPORT_STD template <class _Ty>
-_NODISCARD constexpr _Ty&& forward(remove_reference_t<_Ty>&& _Arg) noexcept { // forward an rvalue as an rvalue
+_NODISCARD _MSVC_INTRINSIC constexpr _Ty&& forward(remove_reference_t<_Ty>&& _Arg) noexcept {
     static_assert(!is_lvalue_reference_v<_Ty>, "bad forward call");
     return static_cast<_Ty&&>(_Arg);
 }
 
 _EXPORT_STD template <class _Ty>
-_NODISCARD constexpr remove_reference_t<_Ty>&& move(_Ty&& _Arg) noexcept { // forward _Arg as movable
+_NODISCARD _MSVC_INTRINSIC constexpr remove_reference_t<_Ty>&& move(_Ty&& _Arg) noexcept {
     return static_cast<remove_reference_t<_Ty>&&>(_Arg);
 }
 
 _EXPORT_STD template <class _Ty>
-_NODISCARD constexpr conditional_t<!is_nothrow_move_constructible_v<_Ty> && is_copy_constructible_v<_Ty>, const _Ty&,
-    _Ty&&>
-    move_if_noexcept(_Ty& _Arg) noexcept { // forward _Arg as movable, sometimes
+_NODISCARD _MSVC_INTRINSIC constexpr //
+    conditional_t<!is_nothrow_move_constructible_v<_Ty> && is_copy_constructible_v<_Ty>, const _Ty&, _Ty&&>
+    move_if_noexcept(_Ty& _Arg) noexcept {
     return _STD move(_Arg);
 }
 
diff --git a/stl/inc/utility b/stl/inc/utility
@@ -820,7 +820,7 @@ _EXPORT_STD [[noreturn]] __forceinline void unreachable() noexcept /* strengthen
 }
 
 _EXPORT_STD template <class _Ty, class _Uty>
-_NODISCARD constexpr auto&& forward_like(_Uty&& _Ux) noexcept {
+_NODISCARD _MSVC_INTRINSIC constexpr auto&& forward_like(_Uty&& _Ux) noexcept {
     static_assert(_Can_reference<_Ty>, "std::forward_like's first template argument must be a referenceable type.");
 
     using _UnrefT = remove_reference_t<_Ty>;
diff --git a/stl/inc/yvals_core.h b/stl/inc/yvals_core.h
@@ -622,9 +622,11 @@
 #pragma push_macro("msvc")
 #pragma push_macro("known_semantics")
 #pragma push_macro("noop_dtor")
+#pragma push_macro("intrinsic")
 #undef msvc
 #undef known_semantics
 #undef noop_dtor
+#undef intrinsic
 
 #ifndef __has_cpp_attribute
 #define _HAS_MSVC_ATTRIBUTE(x) 0
@@ -650,7 +652,16 @@
 #define _MSVC_NOOP_DTOR
 #endif
 
+// Should we use [[msvc::intrinsic]] allowing the compiler to implement the
+// behavior of certain trivial functions?
+#if _HAS_MSVC_ATTRIBUTE(intrinsic)
+#define _MSVC_INTRINSIC [[msvc::intrinsic]]
+#else
+#define _MSVC_INTRINSIC
+#endif
+
 #undef _HAS_MSVC_ATTRIBUTE
+#pragma pop_macro("intrinsic")
 #pragma pop_macro("noop_dtor")
 #pragma pop_macro("known_semantics")
 #pragma pop_macro("msvc")

Original file line number	Diff line number	Diff line change
`@@ -820,7 +820,7 @@ _EXPORT_STD [[noreturn]] __forceinline void unreachable() noexcept /* strengthen`
`820`	`820`	`}`
`821`	`821`
`822`	`822`	`_EXPORT_STD template <class _Ty, class _Uty>`
`823`		`-_NODISCARD constexpr auto&& forward_like(_Uty&& _Ux) noexcept {`
	`823`	`+_NODISCARD _MSVC_INTRINSIC constexpr auto&& forward_like(_Uty&& _Ux) noexcept {`
`824`	`824`	`static_assert(_Can_reference<_Ty>, "std::forward_like's first template argument must be a referenceable type.");`
`825`	`825`
`826`	`826`	`using _UnrefT = remove_reference_t<_Ty>;`