Re: [PATCH] Don't check can_vec_perm_const_p for nonlinear iv_init when it's constant.

[Hongtao Liu <crazylht@gmail.com>]

On Wed, Sep 21, 2022 at 3:41 PM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Wed, Sep 21, 2022 at 1:41 AM liuhongt via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > When init_expr is INTEGER_CST or REAL_CST, can_vec_perm_const_p is not
> > necessary since there's no real vec_perm needed, but
> > vec_gen_perm_mask_checked will gcc_assert (can_vec_perm_const_p). So
> > it's better to use vec_gen_perm_mask_any in
> > vect_create_nonlinear_iv_init.
>
> and the VEC_PERM build will fold the permute away?
Yes, it's just a const vector. [ c, -c, c, c, .. ].
>
> > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > Ok for trunk?
>
> OK.
>
> Thanks,
> Richard.
>
> > gcc/ChangeLog:
> >
> >         PR tree-optimization/106963
> >         * tree-vect-loop.cc (vect_create_nonlinear_iv_init): Use
> >         vec_gen_perm_mask_any instead of vec_gen_perm_mask_check.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.target/i386/pr106963.c: New test.
> > ---
> >  gcc/testsuite/gcc.target/i386/pr106963.c | 14 ++++++++++++++
> >  gcc/tree-vect-loop.cc                    |  5 ++++-
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> >  create mode 100644 gcc/testsuite/gcc.target/i386/pr106963.c
> >
> > diff --git a/gcc/testsuite/gcc.target/i386/pr106963.c b/gcc/testsuite/gcc.target/i386/pr106963.c
> > new file mode 100644
> > index 00000000000..9f2d20e2523
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.target/i386/pr106963.c
> > @@ -0,0 +1,14 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O2 -mavx -mno-avx2" } */
> > +
> > +void
> > +foo_neg_const (int *a)
> > +{
> > +  int i, b = 1;
> > +
> > +  for (i = 0; i < 1000; i++)
> > +    {
> > +      a[i] = b;
> > +      b = -b;
> > +    }
> > +}
> > diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> > index 9c434b66c5b..aabdc6f2d81 100644
> > --- a/gcc/tree-vect-loop.cc
> > +++ b/gcc/tree-vect-loop.cc
> > @@ -8356,8 +8356,11 @@ vect_create_nonlinear_iv_init (gimple_seq* stmts, tree init_expr,
> >             sel[2 * i + 1] = i + nunits;
> >           }
> >         vec_perm_indices indices (sel, 2, nunits);
> > +       /* Don't use vect_gen_perm_mask_checked since can_vec_perm_const_p may
> > +          fail when vec_init is const vector. In that situation vec_perm is not
> > +          really needed.  */
> >         tree perm_mask_even
> > -         = vect_gen_perm_mask_checked (vectype, indices);
> > +         = vect_gen_perm_mask_any (vectype, indices);
> >         vec_init = gimple_build (stmts, VEC_PERM_EXPR,
> >                                  vectype,
> >                                  vec_init, vec_neg,
> > --
> > 2.18.1
> >



-- 
BR,
Hongtao