libstdc++: ppc: conditionalize vsx-only simd intrinsics

  libstdc++'s bits/simd.h section for PPC (Altivec) defines various
intrinsic vector types that are only available along with VSX: 64-bit
long double, double, (un)signed long long, and 64-bit (un)signed long.

experimental/simd/standard_abi_usable{,_2}.cc tests error out reporting
the unmet requirements when the target cpu doesn't enable VSX.  Make the
reported instrinsic types conditional on VSX so that <experimental/simd>
can be used on ppc variants that do not have VSX support.

Regstrapped on powerpc64el-linux-gnu.  Ok to install?

This is also relevant for gcc-11.  Tested with
x86_64-linux-gnu-x-ppc64-vx7r2.  Ok for gcc-11?


for  libstdc++-v3/ChangeLog

	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
	for double, long long, and 64-bit long and 64-bit long double
	intrinsic types.
---
 libstdc++-v3/include/experimental/bits/simd.h |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
  

Hi!

On Thu, Apr 28, 2022 at 03:09:54AM -0300, Alexandre Oliva wrote:
> libstdc++'s bits/simd.h section for PPC (Altivec) defines various
> intrinsic vector types that are only available along with VSX: 64-bit
> long double, double, (un)signed long long, and 64-bit (un)signed long.
> 
> experimental/simd/standard_abi_usable{,_2}.cc tests error out reporting
> the unmet requirements when the target cpu doesn't enable VSX.  Make the
> reported instrinsic types conditional on VSX so that <experimental/simd>
> can be used on ppc variants that do not have VSX support.

> 	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
> 	for double, long long, and 64-bit long and 64-bit long double
> 	intrinsic types.

> --- a/libstdc++-v3/include/experimental/bits/simd.h
> +++ b/libstdc++-v3/include/experimental/bits/simd.h
> @@ -2430,17 +2430,23 @@ template <typename _Tp>
>    template <>                                                                  \
>      struct __intrinsic_type_impl<_Tp> { using type = __vector _Tp; }
>  _GLIBCXX_SIMD_PPC_INTRIN(float);
> +# ifdef __VSX__

No space after # (here and everywhere else).

>  #ifndef __VSX__
> -    static_assert(!is_same_v<_Tp, double>,
> -		  "no __intrinsic_type support for double on PPC w/o VSX");
> +    static_assert(!(is_same_v<_Tp, double>
> +		    || (_S_is_ldouble && sizeof(long double) == sizeof(double))),
> +		  "no __intrinsic_type support for [long] double on PPC w/o VSX");
>  #endif

This change isn't in the changelog.  The message should not say "long
double" without qualifying it as "64-bit long double".  It is probably
best to just keep the message as-is, the other possibilities for long
double aren't supported either, not even with VSX, and all this becomes
much too complicated to put in a simple error message.  It confuses the
poor user, as well.

Alternatively you can make it two separate error messages, one for
double, one for 64-bit long double.

Okay for trunk without this part of the patch, and the spaces after the
hash signs deleted.  Or send a new patch with the "[long] double" thing
fixed?

Thanks!


Segher
  

On Thursday, 28 April 2022 08:09:54 CEST Alexandre Oliva via Gcc-patches 
wrote:
> libstdc++'s bits/simd.h section for PPC (Altivec) defines various
> intrinsic vector types that are only available along with VSX: 64-bit
> long double, double, (un)signed long long, and 64-bit (un)signed long.

Oh, so uttering `__vector double` is ill-formed (now) without VSX? I'm fairly 
certain I tested without VSX and the __intrinsic_type_impl definitions were 
fine.

> experimental/simd/standard_abi_usable{,_2}.cc tests error out reporting
> the unmet requirements when the target cpu doesn't enable VSX.  Make the
> reported instrinsic types conditional on VSX so that <experimental/simd>
> can be used on ppc variants that do not have VSX support.

IIRC this will break other valid uses. You'd have to run `make check-simd` 
(see libstdc++-v3/testsuite/experimental/simd/README.md) to be certain nothing 
breaks. I will also take a look.

> Regstrapped on powerpc64el-linux-gnu.  Ok to install?
> 
> This is also relevant for gcc-11.  Tested with
> x86_64-linux-gnu-x-ppc64-vx7r2.  Ok for gcc-11?
> 
> 
> for  libstdc++-v3/ChangeLog
> 
> 	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
> 	for double, long long, and 64-bit long and 64-bit long double
> 	intrinsic types.
> ---
>  libstdc++-v3/include/experimental/bits/simd.h |   11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/libstdc++-v3/include/experimental/bits/simd.h
> b/libstdc++-v3/include/experimental/bits/simd.h index
> 82e9841195e1d..66c07127ec435 100644
> --- a/libstdc++-v3/include/experimental/bits/simd.h
> +++ b/libstdc++-v3/include/experimental/bits/simd.h
> @@ -2430,17 +2430,23 @@ template <typename _Tp>
>    template <>                                                              
>    \ struct __intrinsic_type_impl<_Tp> { using type = __vector _Tp; }
> _GLIBCXX_SIMD_PPC_INTRIN(float);
> +# ifdef __VSX__
>  _GLIBCXX_SIMD_PPC_INTRIN(double);
> +# endif
>  _GLIBCXX_SIMD_PPC_INTRIN(signed char);
>  _GLIBCXX_SIMD_PPC_INTRIN(unsigned char);
>  _GLIBCXX_SIMD_PPC_INTRIN(signed short);
>  _GLIBCXX_SIMD_PPC_INTRIN(unsigned short);
>  _GLIBCXX_SIMD_PPC_INTRIN(signed int);
>  _GLIBCXX_SIMD_PPC_INTRIN(unsigned int);
> +# if defined __VSX__ || __LONG_WIDTH__ == 32
>  _GLIBCXX_SIMD_PPC_INTRIN(signed long);
>  _GLIBCXX_SIMD_PPC_INTRIN(unsigned long);
> +# endif
> +# ifdef __VSX__
>  _GLIBCXX_SIMD_PPC_INTRIN(signed long long);
>  _GLIBCXX_SIMD_PPC_INTRIN(unsigned long long);
> +# endif
>  #undef _GLIBCXX_SIMD_PPC_INTRIN
> 
>  template <typename _Tp, size_t _Bytes>
> @@ -2452,8 +2458,9 @@ template <typename _Tp, size_t _Bytes>
>      static_assert(!(_S_is_ldouble && sizeof(long double) > sizeof(double)),
> "no __intrinsic_type support for long double on PPC");
>  #ifndef __VSX__
> -    static_assert(!is_same_v<_Tp, double>,
> -		  "no __intrinsic_type support for double on PPC w/o VSX");
> +    static_assert(!(is_same_v<_Tp, double>
> +		    || (_S_is_ldouble && sizeof(long double) == 
sizeof(double))),
> +		  "no __intrinsic_type support for [long] double on PPC w/o 
VSX");

The missing condition here was an incorrect omission. With -mlong-double-64 
and without VSX no assertion caught the issue.

IIRC, a user won't get to see this error message unless there's a bug in the 
simd library implementation, so the error message is good enough for me. (It's 
talking about __intrinsic_type, the user would be lost in any case.)

>  #endif
>      using type =
>        typename __intrinsic_type_impl<
  

On Thu, Apr 28, 2022 at 03:56:18PM +0200, Matthias Kretz wrote:
> On Thursday, 28 April 2022 08:09:54 CEST Alexandre Oliva via Gcc-patches 
> wrote:
> > libstdc++'s bits/simd.h section for PPC (Altivec) defines various
> > intrinsic vector types that are only available along with VSX: 64-bit
> > long double, double, (un)signed long long, and 64-bit (un)signed long.
> 
> Oh, so uttering `__vector double` is ill-formed (now) without VSX? I'm fairly 
> certain I tested without VSX and the __intrinsic_type_impl definitions were 
> fine.

It always was undefined (and did not work):
  error: use of 'double' in AltiVec types is invalid without '-mvsx'


Segher
  

On Apr 28, 2022, Segher Boessenkool <segher@kernel.crashing.org> wrote:

> On Thu, Apr 28, 2022 at 03:09:54AM -0300, Alexandre Oliva wrote:

>> +# ifdef __VSX__

> No space after # (here and everywhere else).

'k, thanks

>> +		  "no __intrinsic_type support for [long] double on PPC w/o VSX");

> This change isn't in the changelog.

It is, it's just that long double is dealt with differently from the
other types, so requiring VSX for it takes a different form:

> 	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
> 	for double, long long, and 64-bit long and 64-bit long double
> 	intrinsic types.                           ^^^^^^^^^^^^^^^^^^



> The message should not say "long
> double" without qualifying it as "64-bit long double".

How about qualifying both such messages as in this incremental patchlet:

@@ -2456,11 +2456,11 @@ template <typename _Tp, size_t _Bytes>
     static constexpr bool _S_is_ldouble = is_same_v<_Tp, long double>;
     // allow _Tp == long double with -mlong-double-64
     static_assert(!(_S_is_ldouble && sizeof(long double) > sizeof(double)),
-		  "no __intrinsic_type support for long double on PPC");
+		  "no __intrinsic_type support for 128-bit floating point on PPC");
 #ifndef __VSX__
     static_assert(!(is_same_v<_Tp, double>
 		    || (_S_is_ldouble && sizeof(long double) == sizeof(double))),
-		  "no __intrinsic_type support for [long] double on PPC w/o VSX");
+		  "no __intrinsic_type support for 64-bit floating point on PPC w/o VSX");
 #endif
     using type =
       typename __intrinsic_type_impl<

> Okay for trunk without this part of the patch, and the spaces after the
> hash signs deleted.  Or send a new patch with the "[long] double" thing
> fixed?

Thanks, awaiting feedback on the suggestion above to post the consolidated patch.
  

On Friday, 29 April 2022 03:53:40 CEST Alexandre Oliva via Gcc-patches wrote:
> Thanks, awaiting feedback on the suggestion above to post the consolidated
> patch.

LGTM. I think this improves clarity for the __intrisic_type static assertions 
significantly.

And don't bother with my other mail. If `__vector double` without VSX was 
always ill-formed then I must be misremembering something.

Cheers,
  Matthias
  

Hi!

On Thu, Apr 28, 2022 at 10:53:40PM -0300, Alexandre Oliva wrote:
> On Apr 28, 2022, Segher Boessenkool <segher@kernel.crashing.org> wrote:
> > On Thu, Apr 28, 2022 at 03:09:54AM -0300, Alexandre Oliva wrote:
> >> +		  "no __intrinsic_type support for [long] double on PPC w/o VSX");
> > This change isn't in the changelog.
> 
> It is, it's just that long double is dealt with differently from the
> other types, so requiring VSX for it takes a different form:

It changes a diagnostic message.  Incorrectly, even.  The changelog does
not talk about this.

The only thing I use changelogs for nowadays is to help reviewing code.
So when things are missing it stands out like a sore thumb.

> > 	* include/experimental/bits/simd.h [__ALTIVEC__]: Require VSX
> > 	for double, long long, and 64-bit long and 64-bit long double
> > 	intrinsic types.                           ^^^^^^^^^^^^^^^^^^

Yes, that does not talk about changing a diagnostic message.

> > The message should not say "long
> > double" without qualifying it as "64-bit long double".
> 
> How about qualifying both such messages as in this incremental patchlet:

Send full patches always please.  Not patches relative to some
non-existing state :-)

Thanks,


Segher