On Wed, 13 Sept 2023 at 23:52, Patrick Palka via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
OK, thanks.
>
> -- >8 --
>
> For std::to_chars:
>
> The constrained alias __integer_to_chars_result_type seems unnecessary
> ever since r10-3080-g28f0075742ed58 got rid of the only public overload
> which used it. Now only non-public overloads are constrained by it
> (through their return type) and these non-public overloads aren't used
> in a SFINAE context, so the constraints have no observable effect. So
> this patch gets rid of this alias, which greatly reduces the symbol
> sizes of the affected functions (since the expanded alias is quite
> large).
>
> For std::from_chars:
>
> We can't get rid of the corresponding alias because it's constrains
> the public integer std::from_chars overload. But we can avoid having
> the constraint bloat the mangled name by instead encoding it as a
> defaulted template parameter. We use the non-type parameter form
>
> enable_if_t<..., int> = 0
>
> instead of the type parameter form
>
> typename = enable_if_t<...>
>
> because the type form can be circumvented by providing an explicit template
> argument to type parameter, e.g. 'std::from_chars<int, void>(...)', so the
> non-type form seems like the more robust choice.
>
> In passing, use __is_standard_integer in the constraint.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/charconv (__detail::__integer_to_chars_result_type):
> Remove.
> (__detail::__to_chars_16): Use to_chars_result as return type.
> (__detail::__to_chars_10): Likewise.
> (__detail::__to_chars_8): Likewise.
> (__detail::__to_chars_2): Likewise.
> (__detail::__to_chars_i): Likewise.
> (__detail::__integer_from_chars_result_type): Pull out enable_if_t
> condition into and replace with ...
> (__detail::__integer_from_chars_enabled): ... this. Use
> __is_standard_integer instead of __is_signed_integer and
> __is_unsigned_integer.
> (from_chars): Encode constraint as a defaulted non-type template
> parameter instead of within the return type.
> ---
> libstdc++-v3/include/std/charconv | 33 ++++++++++---------------------
> 1 file changed, 10 insertions(+), 23 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/charconv
> b/libstdc++-v3/include/std/charconv
> index 01711d38576..ec25ae139ba 100644
> --- a/libstdc++-v3/include/std/charconv
> +++ b/libstdc++-v3/include/std/charconv
> @@ -79,17 +79,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> namespace __detail
> {
> - template<typename _Tp>
> - using __integer_to_chars_result_type
> - = enable_if_t<__or_<__is_signed_integer<_Tp>,
> - __is_unsigned_integer<_Tp>,
> -#if defined __SIZEOF_INT128__ && defined __STRICT_ANSI__
> - is_same<_Tp, signed __int128>,
> - is_same<_Tp, unsigned __int128>,
> -#endif
> - is_same<char, remove_cv_t<_Tp>>>::value,
> - to_chars_result>;
> -
> // Pick an unsigned type of suitable size. This is used to reduce the
> // number of specializations of __to_chars_len, __to_chars etc. that
> // get instantiated. For example, to_chars<char> and to_chars<short>
> @@ -162,7 +151,7 @@ namespace __detail
> }
>
> template<typename _Tp>
> - constexpr __integer_to_chars_result_type<_Tp>
> + constexpr to_chars_result
> __to_chars_16(char* __first, char* __last, _Tp __val) noexcept
> {
> static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation
> bug");
> @@ -208,7 +197,7 @@ namespace __detail
> }
>
> template<typename _Tp>
> - constexpr __integer_to_chars_result_type<_Tp>
> + constexpr to_chars_result
> __to_chars_10(char* __first, char* __last, _Tp __val) noexcept
> {
> static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation
> bug");
> @@ -231,7 +220,7 @@ namespace __detail
> }
>
> template<typename _Tp>
> - constexpr __integer_to_chars_result_type<_Tp>
> + constexpr to_chars_result
> __to_chars_8(char* __first, char* __last, _Tp __val) noexcept
> {
> static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation
> bug");
> @@ -284,7 +273,7 @@ namespace __detail
> }
>
> template<typename _Tp>
> - constexpr __integer_to_chars_result_type<_Tp>
> + constexpr to_chars_result
> __to_chars_2(char* __first, char* __last, _Tp __val) noexcept
> {
> static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation
> bug");
> @@ -320,7 +309,7 @@ namespace __detail
> } // namespace __detail
>
> template<typename _Tp>
> - constexpr __detail::__integer_to_chars_result_type<_Tp>
> + constexpr to_chars_result
> __to_chars_i(char* __first, char* __last, _Tp __value, int __base = 10)
> {
> __glibcxx_assert(2 <= __base && __base <= 36);
> @@ -548,17 +537,15 @@ namespace __detail
> }
>
> template<typename _Tp>
> - using __integer_from_chars_result_type
> - = enable_if_t<__or_<__is_signed_integer<_Tp>,
> - __is_unsigned_integer<_Tp>,
> - is_same<char, remove_cv_t<_Tp>>>::value,
> - from_chars_result>;
> + constexpr bool __integer_from_chars_enabled
> + = __or_<__is_standard_integer<_Tp>, is_same<char,
> remove_cv_t<_Tp>>>::value;
>
> } // namespace __detail
>
> /// std::from_chars for integral types.
> - template<typename _Tp>
> - _GLIBCXX23_CONSTEXPR __detail::__integer_from_chars_result_type<_Tp>
> + template<typename _Tp,
> + enable_if_t<__detail::__integer_from_chars_enabled<_Tp>, int> = 0>
> + _GLIBCXX23_CONSTEXPR from_chars_result
> from_chars(const char* __first, const char* __last, _Tp& __value,
> int __base = 10)
> {
> --
> 2.42.0.158.g94e83dcf5b
>
