Re: [PATCH] testsuite: update requires for powerpc/float128-cmp2-runnable.c

[Jiufu Guo <guojiufu@linux.ibm.com>]

Hi,

Segher Boessenkool <segher@kernel.crashing.org> writes:

> On Tue, Apr 11, 2023 at 05:40:09PM +0800, Kewen.Lin wrote:
>> on 2023/4/11 17:14, guojiufu wrote:
>> > Thanks for raising this concern.
>> > The behavior to check about bif on FLOAT128_HW and emit an error message for
>> > requirements on quad-precision is added in gcc12. This is why gcc12 fails to
>> > compile the case on -m32.
>> > 
>> > Before gcc12, altivec_resolve_overloaded_builtin will return the overloaded
>> > result directly, and does not check more about the result function.
>> 
>> Thanks for checking, I wonder which commit caused this behavior change and what's
>> the underlying justification?  I know there is one new bif handling framework
>> introduced in gcc12, not sure the checking condition was changed together or by
>> a standalone commit.  Anyway, apparently the conditions for the support of these
>> bifs are different on gcc-11 and gcc-12, I wonder why it changed.  As mentioned
>> above, PR108758's c#1 said this case (bifs) work well on gcc-11, I suspected the
>> condition change was an overkill, that's why I asked.
>
> It almost certainly was an oversight.  The new builtin framework changed
> so many things, there was bound to be some breakage to go with all the
> good things it brought.

Yes, the condition checking on gcc-12 is different from gcc-11. In
gcc-11, the condition on overloaded bif is not checked.
And, there are a few commits related to the bifs change. e.g.
r12-4977-ga28cfe49203705 introduces a new bif expand function which has
the ability to check more bif's target requirements like ieee128_hw.
And another commit changes the error message (r12-6684).

>
> So what is the actual thing going wrong?  QP insns work fine and are
> valid on all systems and environments, BE or LE, 32-bit or 64-bit.  Of
> course you cannot use the "long double" type for those everywhere, but
> that is a very different thing.

Currently, when compiling bif __builtin_vsx_scalar_cmp_exp_qp_eq,
gcc generates error message:
error: '__builtin_vsx_scalar_cmp_exp_qp_eq' requires quad-precision
floating-point arithmetic

IMHO, this error would be ok.  Because it makes sense that this bif
needs ieee128_hw.

BR,
Jeff (Jiufu)

>
>
> Segher