> From: Jonathan Wakely <jwak...@redhat.com> > Cc: Hans-Peter Nilsson <h...@axis.com> > Date: Thu, 1 Feb 2024 15:36:50 +0000
> I plan to push this to trunk soon. > > CC HP for visibility of the change affecting cris-elf. In practice it > shouldn't make any difference to any sensible code. It only affects > C++20 mode (and later), and only changes the size of std::formatter > objects which are typically only created by the library headers > themselves, and only on the stack (when using std::format and other new > C++20 APIs related to it). > > -- >8 -- > > This ensures that the unused bits will be zero-initialized reliably, and > so can be used later by assigning them values in formatter > specializations. For example, formatters for std::chrono will need to > use an extra bit for a boolean to optimize the conversions between > locale encodings and UTF-8. > > This will result in an ABI change for targets that use 1-byte alignment > for all integral types, e.g. cris-elf. Thanks for the heads-up, but don't worry about ABI changes for cris-elf. Not speaking for other platforms with default-packed layout or where ABI structure layout alignment implies a change due to PCC_BITFIELD_TYPE_MATTERS and the "unsigned long" bitfield type. That last one may matter though. > We can't do that once C++20 > support is non-experimental and ABI stable, so do it now before GCC 14 > is released. > > libstdc++-v3/ChangeLog: > > * include/std/format (__format::_Spec::_M_reserved): Define a > new bit-field member in place of padding bits. > --- > libstdc++-v3/include/std/format | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format > index 0eca8b58bfa..6c958bc11a5 100644 > --- a/libstdc++-v3/include/std/format > +++ b/libstdc++-v3/include/std/format > @@ -406,6 +406,7 @@ namespace __format > _WidthPrec _M_width_kind : 2; > _WidthPrec _M_prec_kind : 2; > _Pres_type _M_type : 4; > + unsigned long _M_reserved : 17; > unsigned short _M_width; > unsigned short _M_prec; > char32_t _M_fill = ' '; > -- > 2.43.0 >
