On Tue, Feb 25, 2025 at 1:05 AM Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Thu, Feb 20, 2025 at 01:11:25PM -0800, Andrew Pinski wrote:
> > So what is happening here is that after r15-268-g9dbff9c05520a7,
> > a move instruction still exists after combine and the register
> > allocator choses different register allocation order for the xor
> > and because the input operand of lzcntq is not the same as output
> > operand, there is an extra xor that happens (due to an errata).
> >
> > This fixes the testcase by using loading from a pointer instead
> > of a function argument directly. The register allocator has more
> > freedom since the load has no hard register associated with it (rdi)
> > so it can be in eax register right away.
> >
> > Tested for both -m32 and -m64 on x86_64-linux-gnu.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR testsuite/115028
> > * gcc.target/i386/pr101950-2.c:
>
> Please describe what you changed here.
>
> Otherwise LGTM.
This the changelog which I pushed the patch with:
PR testsuite/115028
* gcc.target/i386/pr101950-2.c: Use a pointer argument instead
of the argument directly.
Thanks,
Andrew
> >
> > Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> > ---
> > gcc/testsuite/gcc.target/i386/pr101950-2.c | 13 +++++++++----
> > 1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/gcc/testsuite/gcc.target/i386/pr101950-2.c
> > b/gcc/testsuite/gcc.target/i386/pr101950-2.c
> > index 896f1b46414..ccc361e3a46 100644
> > --- a/gcc/testsuite/gcc.target/i386/pr101950-2.c
> > +++ b/gcc/testsuite/gcc.target/i386/pr101950-2.c
> > @@ -6,14 +6,19 @@
> > /* { dg-final { scan-assembler-times "\txor\[ql]\t" 2 } } */
> > /* { dg-final { scan-assembler-times "\tsar\[ql]\t|\tcltd" 2 } } */
> >
> > +/* Use pointers to avoid register allocation difference due to argument
> > + and return register being different and the difference in selecting eax
> > + for one the result of the xor vs selecting rdi due to the order of the
> > + shift vs the not shift. */
> > +
> > int
> > -foo (long x)
> > +foo (long *x)
> > {
> > - return __builtin_clrsbl (x);
> > + return __builtin_clrsbl (*x);
> > }
> >
> > int
> > -bar (int x)
> > +bar (int *x)
> > {
> > - return __builtin_clrsb (x);
> > + return __builtin_clrsb (*x);
> > }
> > --
> > 2.43.0
>
> Jakub
>
