Re: [PATCH] Fix target/101934: aarch64 memset code creates unaligned stores for -mstrict-align

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Sep 1, 2021 at 1:52 AM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> apinski--- via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > From: Andrew Pinski <apinski@marvell.com>
> >
> > The problem here is the aarch64_expand_setmem code did not check
> > STRICT_ALIGNMENT if it is creating an overlapping store.
> > This patch adds that check and the testcase works.
> >
> > gcc/ChangeLog:
> >
> >       PR target/101934
> >       * config/aarch64/aarch64.c (aarch64_expand_setmem):
> >       Check STRICT_ALIGNMENT before creating an overlapping
> >       store.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       PR target/101934
> >       * gcc.target/aarch64/memset-strict-align-1.c: New test.
>
> OK, thanks.

Applied now also on the GCC 11 branch.

Thanks,
Andrew

>
> Richard
>
> > ---
> >  gcc/config/aarch64/aarch64.c                  |  4 +--
> >  .../aarch64/memset-strict-align-1.c           | 28 +++++++++++++++++++
> >  2 files changed, 30 insertions(+), 2 deletions(-)
> >  create mode 100644 gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c
> >
> > diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> > index 3213585a588..26d59ba1e13 100644
> > --- a/gcc/config/aarch64/aarch64.c
> > +++ b/gcc/config/aarch64/aarch64.c
> > @@ -23566,8 +23566,8 @@ aarch64_expand_setmem (rtx *operands)
> >        /* Do certain trailing copies as overlapping if it's going to be
> >        cheaper.  i.e. less instructions to do so.  For instance doing a 15
> >        byte copy it's more efficient to do two overlapping 8 byte copies than
> > -      8 + 4 + 2 + 1.  */
> > -      if (n > 0 && n < copy_limit / 2)
> > +      8 + 4 + 2 + 1.  Only do this when -mstrict-align is not supplied.  */
> > +      if (n > 0 && n < copy_limit / 2 && !STRICT_ALIGNMENT)
> >       {
> >         next_mode = smallest_mode_for_size (n, MODE_INT);
> >         int n_bits = GET_MODE_BITSIZE (next_mode).to_constant ();
> > diff --git a/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c b/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c
> > new file mode 100644
> > index 00000000000..5cdc8a44968
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/aarch64/memset-strict-align-1.c
> > @@ -0,0 +1,28 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-Os -mstrict-align" } */
> > +
> > +struct s { char x[95]; };
> > +void foo (struct s *);
> > +void bar (void) { struct s s1 = {}; foo (&s1); }
> > +
> > +/* memset (s1 = {}, sizeof = 95) should be expanded out
> > +   such that there are no overlap stores when -mstrict-align
> > +   is in use.
> > +   so 2 pair 16 bytes stores (64 bytes).
> > +   1 16 byte stores
> > +   1 8 byte store
> > +   1 4 byte store
> > +   1 2 byte store
> > +   1 1 byte store
> > +   */
> > +
> > +/* { dg-final { scan-assembler-times "stp\tq" 2 } } */
> > +/* { dg-final { scan-assembler-times "str\tq" 1 } } */
> > +/* { dg-final { scan-assembler-times "str\txzr" 1 } } */
> > +/* { dg-final { scan-assembler-times "str\twzr" 1 } } */
> > +/* { dg-final { scan-assembler-times "strh\twzr" 1 } } */
> > +/* { dg-final { scan-assembler-times "strb\twzr" 1 } } */
> > +
> > +/* Also one store pair for the frame-pointer and the LR. */
> > +/* { dg-final { scan-assembler-times "stp\tx" 1 } } */
> > +