On Fri, 2023-08-18 at 14:39 +0800, chenxiaolong wrote:
> 在 2023-08-17四的 15:08 +0000，Joseph Myers写道：
> > On Thu, 17 Aug 2023, Xi Ruoyao via Gcc-patches wrote:
> >
> > > So I guess we just need
> > >
> > > builtin_define ("__builtin_fabsq=__builtin_fabsf128");
> > > builtin_define ("__builtin_nanq=__builtin_nanf128");
> > >
> > > etc. to map the "q" builtins to "f128" builtins if we really need
> > > the
> > > "q" builtins.
> > >
> > > Joseph: the problem here is many customers of LoongArch CPUs wish
> > > to
> > > compile their old code with minimal change. Is it acceptable to
> > > add
> > > these builtin_define's like rs6000-c.cc? Note "a new architecture"
> > > does
> > > not mean we'll only compile post-C2x-era programs onto it.
> >
> > The powerpc support for __float128 started in GCC 6, predating the
> > support
> > for _FloatN type names, built-in functions etc. in GCC 7 - that's
> > why
> > there's such backwards compatibility support there. That name only
> > exists
> > on a few architectures.
> >
> > If people really want to compile code using the old __float128 names
> > for
> > LoongArch I suppose you could have such #defines, but it would be
> > better
> > for people to make their code use the standard names (as supported
> > from
> > GCC 7 onwards, though only from GCC 13 in C++) and then put
> > backwards
> > compatibility in their code for using the __float128 names if they
> > want to
> > support the type with older GCC (GCC 6 or before for C; GCC 12 or
> > before
> > for C++) on x86_64 / i386 / powerpc / ia64. Such backwards
> > compatibility
> > in user code is more likely to be relevant for C++ than for C, given
> > how
> > the C++ support was added to GCC much more recently. (Note: I
> > haven't
> > checked when other compilers added support for the _Float128 name or
> > associated built-in functions, whether for C or for C++, which might
> > also
> > affect when user code wants such compatibility.)
> >
> Thank you for your valuable comments. On the LoongArch architecture,
> the "__float128" type is associated with float128_type_node and the "q"
> suffix function is mapped to the "f128" function. This allows
> compatibility with both "__float128" and "_Float128" types in the GCC
> compiler. The new code is modified as follows:
> Add the following to the loongarch-builtins.c file:
> +lang_hooks.types.register_builtin_type (float128_type_node,
> "__float128");
> Add the following to the loongarch-c.c file:
> +builtin_define ("__builtin_fabsq=__builtin_fabsf128");
> +builtin_define ("__builtin_copysignq=__builtin_copysignf128");
> +builtin_define ("__builtin_nanq=__builtin_nanf128");
> +builtin_define ("__builtin_nansq=__builtin_nansf128");
> +builtin_define ("__builtin_infq=__builtin_inff128");
> +builtin_define ("__builtin_huge_valq=__builtin_huge_valf128");
>
> The regression tests of the six functions were added without problems.
> However, the implementation of the __builtin_nansq() function does not
> get the result we want. The questions are as follows:
> x86_64:
> _Float128 ret=__builtin_nansf128("NAN");
>
> compiled to (with gcc test.c -O2 ):
> .cfi_offset 1, -8
> bl %plt(__builtin_nansf128)
> ..
> LoongArch:
> _Float128 ret=__builtin_nansf128("NAN");
> compiled to (with gcc test.c -O2 ):
> .cfi_offset 1, -8
> bl %plt(__builtin_nansf128)
It seems wrong. It should be "bl %plt(nansf128)" instead, without the
__builtin_ prefix so the implementation in libm (from Glibc) will be
used instead. AFAIK __builtin_nan and __builtin_nans are rarely called
with a non-empty tagp so it's not worthy to inline the implementation
for non-empty tagp here.
The same issue happens on x86_64:
call __builtin_nansf128@PLT
__builtin_nanf128 compiles correct:
call nanf128@PLT
I'll see if there is a ticket in https://gcc.gnu.org/bugzilla. If not
I'll create one.
--
Xi Ruoyao <xry...@xry111.site>
School of Aerospace Science and Technology, Xidian University
