Re: [PATCH v2] Explicitly view_convert_expr mask to signed type when folding pblendvb builtins.

[Hongtao Liu <crazylht@gmail.com>]

On Tue, Jun 6, 2023 at 4:23 PM liuhongt <hongtao.liu@intel.com> wrote:
>
> > I think this is a better patch and will always be correct and still
> > get folded at the gimple level (correctly):
> > diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> > index d4ff56ee8dd..02bf5ba93a5 100644
> > --- a/gcc/config/i386/i386.cc
> > +++ b/gcc/config/i386/i386.cc
> > @@ -18561,8 +18561,10 @@ ix86_gimple_fold_builtin (gimple_stmt_iterator *gsi)
> >               tree itype = GET_MODE_INNER (TYPE_MODE (type)) == E_SFmode
> >                 ? intSI_type_node : intDI_type_node;
> >               type = get_same_sized_vectype (itype, type);
> > -             arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
> >             }
> > +         else
> > +           type = signed_type_for (type);
> > +         arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
> >           tree zero_vec = build_zero_cst (type);
> >           tree cmp_type = truth_type_for (type);
> >           tree cmp = gimple_build (&stmts, LT_EXPR, cmp_type, arg2, zero_vec);
> >
> >
>
> Yes, thanks.
>
> Here's the updated patch:
>
> Since mask < 0 will be always false for vector char when
> -funsigned-char, but vpblendvb needs to check the most significant
> bit. The patch explicitly VCE to vector signed char.
>
Pushed to trunk and backport to GCC-13/GCC-12 release branch.(No need
for GCC-11 and earlier since the bug is introduced in GCC12).
>
> gcc/ChangeLog:
>
>         PR target/110108
>         * config/i386/i386.cc (ix86_gimple_fold_builtin): Explicitly
>         view_convert_expr mask to signed type when folding pblendvb
>         builtins.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/i386/pr110108-2.c: New test.
> ---
>  gcc/config/i386/i386.cc                    |  4 +++-
>  gcc/testsuite/gcc.target/i386/pr110108-2.c | 14 ++++++++++++++
>  2 files changed, 17 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr110108-2.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index da20c2c49de..4e594a9c88e 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -18561,8 +18561,10 @@ ix86_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>               tree itype = GET_MODE_INNER (TYPE_MODE (type)) == E_SFmode
>                 ? intSI_type_node : intDI_type_node;
>               type = get_same_sized_vectype (itype, type);
> -             arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
>             }
> +         else
> +           type = signed_type_for (type);
> +         arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
>           tree zero_vec = build_zero_cst (type);
>           tree cmp_type = truth_type_for (type);
>           tree cmp = gimple_build (&stmts, LT_EXPR, cmp_type, arg2, zero_vec);
> diff --git a/gcc/testsuite/gcc.target/i386/pr110108-2.c b/gcc/testsuite/gcc.target/i386/pr110108-2.c
> new file mode 100644
> index 00000000000..2d1d2fd4991
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr110108-2.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-mavx2 -O2 -funsigned-char" } */
> +/* { dg-final { scan-assembler-times "vpblendvb" 2 } } */
> +
> +#include <immintrin.h>
> +__m128i do_stuff_128(__m128i X0, __m128i X1, __m128i X2) {
> +  __m128i Result = _mm_blendv_epi8(X0, X1, X2);
> +  return Result;
> +}
> +
> +__m256i do_stuff_256(__m256i X0, __m256i X1, __m256i X2) {
> +  __m256i Result = _mm256_blendv_epi8(X0, X1, X2);
> +  return Result;
> +}
> --
> 2.39.1.388.g2fc9e9ca3c
>


-- 
BR,
Hongtao