[PATCH 04/11 v3] libstdc++: Make use of __builtin_bit_cast

[Jonathan Wakely]

On Thu, 24 Jun 2021 at 15:11, Jonathan Wakely wrote:
>
> On Thu, 24 Jun 2021 at 15:08, Jakub Jelinek wrote:
> >
> > On Thu, Jun 24, 2021 at 04:01:34PM +0200, Matthias Kretz wrote:
> > > --- a/libstdc++-v3/include/experimental/bits/simd.h
> > > +++ b/libstdc++-v3/include/experimental/bits/simd.h
> > > @@ -1598,7 +1598,9 @@ template <typename _To, typename _From>
> > >    _GLIBCXX_SIMD_INTRINSIC constexpr _To
> > >    __bit_cast(const _From __x)
> > >    {
> > > -    // TODO: implement with / replace by __builtin_bit_cast ASAP
> > > +#if __has_builtin(__builtin_bit_cast)
> >
> > Shouldn't that use #if _GLIBCXX_HAS_BUILTIN(__builtin_bit_cast) in
> > c++config to define a new macro and use that macro here?
> > Though it is true that c++config already uses
> > #if __has_builtin(__builtin_is_constant_evaluated)
> > and so would fail miserably for compilers that don't support __has_builtin
>
> GCC was the last of our supported compilers to implement
> __has_builtin, so for GCC trunk we can assume that it's always
> supported.
>
> The code in c++config.h still has some value for built-ins that aren't
> called __builtin_xxx because older versions of Clang need different
> handling for those. But for __builtin_bit_cast and
> __builtin_is_constant_evaluted we can just use __is_builtin directly.

s/__is_builtin/__has_builtin/