https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106652
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jason at gcc dot gnu.org,
| |ppalka at gcc dot gnu.org,
| |redi at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On targets that do have __float128, I believe we want to mangle it as before
and also handle usual arithmetic conversions etc. the same we did before unless
the
C++23 extended floating-point types are involved.
Which is why I've introduced the float128t_type_node hack, where non-C++ can
continue to do what it did before but for C++ __float128 will be a new distinct
type.
For mangling of std::float{16,32,64,128}_t I'm using the Itanium ABI
_Float{16,32,64,128} mangling, i.e. DF{16,32,64,128}_
This collides with the apparently never really used mangling of
FIXED_POINT_TYPEs
(fixed points are really only supported in C on a few platforms, not in C++,
and at some point they leaked into the C++ FE through 0r and similar literals,
but that has been fixed shortly afterwards).
The patch only introduces _Float{16,32,64,128}, not _Float{32,64,128}x that C
also supports, so I've removed __FLT{32,64,128}X_* predefined macros.
The patch is still incomplete and I'm getting stuck on it (except I can surely
provide testsuite coverage for what is already implemented):
1) there is no bf16/BF16 constant suffix nor underlying type for
std::bfloat16_t
for now; I think we need to come to agreement on how the underlying type
would be called (__bf16 like aarch64/arm/i386 currently have their extension
type?) and how to mangle it (all 3 currently mangle it as u6__bf16) and
if we choose a different keyword for it whether it is distinct from __bf16
2) I haven't implemented the [conv.double] addition:
"with a greater or equal conversion rank ([conv.rank]). A prvalue of
standard
floating-point type can be converted to a prvalue of another standard
floating-point type" - not really sure where it should be done
(but the new cp_compare_floating_point_conversion_ranks function can be
used to compare ranks and subranks)
3) for the [expr.static.cast] addition, I wonder if there is anything to do,
I'd expect it would just work as is
4) for the [expr.arith.conv] changes, I think I've implement those in
cp_common_type, except for the
"Otherwise, the expression is ill-formed."
part where I just return error_mark_node, but cp_common_type doesn't
emit any diagnostics whatsoever, so I wonder if it should be done
somewhere in the callers, or if the function and its wrappers should
get tsubst_flags_t complain argument or what.
5) I've skipped the [over.ics.rank] changes, I'm afraid it is another thing
I'm not really familiar with
6) the library part is unimplemented altogether, the __FLT* macros can be used
to implement numerical limits, but e.g. for the <cmath>/<complex> stuff
not really sure how far can we get for std::float128_t if not on glibc or
on old glibc (guess the others at least when they match float/double
which can be tested through preprocessor macros can be handled by casts
to those types)
