Re: [PATCH] x86: Compile PR 88465 tests with -mtune=generic

On Thu, Aug 20, 2026 at 10:14 AM Liu, Hongtao <[email protected]> wrote:
>
>
>
> > -----Original Message-----
> > From: H.J. Lu <[email protected]>
> > Sent: Thursday, August 20, 2026 9:47 AM
> > To: GCC Patches <[email protected]>; Uros Bizjak
> > <[email protected]>; Liu, Hongtao <[email protected]>
> > Subject: [PATCH] x86: Compile PR 88465 tests with -mtune=generic
> >
> > Compile PR 88465 tests with -mtune=generic to avoid
> >
> > FAIL: gcc.target/i386/avx512bw-pr88465.c scan-assembler-times
> > kxnor[dq][ \t] 2
> > FAIL: gcc.target/i386/avx512dq-pr88465.c scan-assembler-times kxnorb[ \t]
> > 1
> > FAIL: gcc.target/i386/avx512f-pr88465.c scan-assembler-times kxnorw[ \t] 1
> >
> > caused by different code sequence from different default cost models.
>
> It looks like an mis-optimization under tune=znver4, I check -mtune=sapphirerapids is ok.
> Assume kxnorb should be fastest way to move -1 to k register, not load it from constant pool.

It is due to znver4 cost model.  I opened:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126959

But changing znver4 cost model may cause other regressions.

> >
> > PR testsuite/126923
> > * gcc.target/i386/avx512bw-pr88465.c (dg-options): Add -mtune=generic.
> > * gcc.target/i386/avx512dq-pr88465.c (dg-options): Likewise.
> > * gcc.target/i386/avx512f-pr88465.c (dg-options): Likewise.
> >
> > --
> > H.J.



-- 
H.J.