libstdc++: Preserve the argument type in basic_format_args [PR119246]

This commits adjust the way how the arguments are stored in the _Arg_value
(and thus basic_format_args), by preserving the types of fixed width
floating-point types, that were previously converted to float, double,
long double.

The _Arg_value union now contains alternatives with std::bfloat16_t,
std::float16_t, std::float32_t, std::float64_t that use pre-existing
_Arg_bf16, _Arg_f16, _Arg_f32, _Arg_f32 argument types.

This does not affect formatting, as specialization of formatters for fixed
width floating-point types formats them by casting to the corresponding
standard floating point type.

For the 128bit floating we need to handle the ppc64 architecture,
(_GLIBCXX_LONG_DOUBLE_ALT128_COMPAT) for which the long double may (per TU
basis) designate either __ibm128 and __ieee128 type, we need to store both
types in the _Arg_value and have two _Arg_types (_Arg_ibm128, _Arg_ieee128).
On other architectures we use extra enumerator value to store __float128,
that is different from long double and _Float128. This is consistent with ppc64,
for which __float128, if present, is same type as __ieee128. We use _Arg_float128
_M_float128 names that deviate from _Arg_fN naming scheme, to emphasize that
this flag is not used for std::float128_t (_Float128) type, that is consistenly
formatted via handle.

The __format::__float128_t type is renamed to __format::__flt128_t, to mitigate
visual confusion between this type and __float128. We also introduce __bflt16_t
typedef instead of using of decltype.

We add new alternative for the _Arg_value and allow them to be accessed via _S_get,
when the types are available. However, we produce and handle corresponding _Arg_type,
only when we can format them. See also r14-3329-g27d0cfcb2b33de.

The formatter<_Float128, _CharT> that formats via __format::__flt128_t is always
provided, when type is available. It is still correct when __format::__flt128_t
is _Float128.

We also provide formatter<__float128, _CharT> that formats via __flt128_t.
As this type may be disabled (-mno-float128), extra care needs to be taken,
for situation when __float128 is same as long double. If the formatter would be
defined in such case, the formatter<long double, _CharT> would be generated
from different specializations, and have different mangling:
  * formatter<__float128, _CharT> if __float128 is present,
  * formatter<__format::__formattable_float, _CharT> otherwise.
To best of my knowledge this happens only on ppc64 for __ieee128 and __float128,
so the formatter is not defined in this case. static_assert is added to detect
other configurations like that. In such case we should replace it with constraint.

	PR libstdc++/119246

libstdc++-v3/ChangeLog:

	* include/std/format (__format::__bflt16_t): Define.
	(_GLIBCXX_FORMAT_F128): Separate value for cases where _Float128
	is used.
	(__format::__float128_t): Renamed to __format::__flt128_t.
	(std::formatter<_Float128, _CharT>): Define always if there is
	formattable 128bit float.
	(std::formatter<__float128, _CharT>): Define.
	(_Arg_type::_Arg_f128): Rename to _Arg_float128 and adjust value.
	(_Arg_type::_Arg_ibm128): Change value to _Arg_ldbl.
	(_Arg_type::_Arg_ieee128): Define as alias to _Arg_float128.
	(_Arg_value::_M_f128): Replaced with _M_ieee128 and _M_float128.
	(_Arg_value::_M_ieee128, _Arg_value::_M_float128)
	(_Arg_value::_M_bf16, _Arg_value::_M_f16, _Arg_value::_M_f32)
	(_Arg_value::_M_f64): Define.
	(_Arg_value::_S_get, basic_format_arg::_S_to_enum): Handle __bflt16,
	_Float16, _Float32, _Float64, and __float128 types.
	(basic_format_arg::_S_to_arg_type): Preserve _bflt16, _Float16,
	_Float32, _Float64 and __float128 types.
	(basic_format_arg::_M_visit): Handle _Arg_float128, _Arg_ieee128,
	_Arg_b16, _Arg_f16, _Arg_f32, _Arg_f64.
	* testsuite/std/format/arguments/args.cc: Updated to illustrate
	that extended floating point types use handles now. Added test
	for __float128.
	* testsuite/std/format/parse_ctx.cc: Extended test to cover class
	to check_dynamic_spec with floating point types and handles.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

0 files changed, 0 insertions, 0 deletions