Re: [PATCH] tree-optimization: [PR103218] Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit

[Richard Biener <richard.guenther@gmail.com>]

On Sat, Nov 13, 2021 at 9:14 PM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> This folds Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit inside match.pd.
> This was already handled in fold-cost by:
> /* A < 0 ? <sign bit of A> : 0 is simply (A & <sign bit of A>).  */
> I have not removed as we only simplify "a ? POW2 : 0" at the gimple level to "a << CST1"
> and fold actually does the reverse of folding "(a<0)<<CST" into "(a<0) ? 1<<CST : 0".
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

Thanks,
Richard.

>         PR tree-optimization/103218
>
> gcc/ChangeLog:
>
>         * match.pd: New pattern for "((type)(a<0)) << SIGNBITOFA".
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/pr103218-1.c: New test.
> ---
>  gcc/match.pd                               | 10 ++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c | 28 ++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index a319aefa808..df31964e02f 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -865,6 +865,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>      { tree utype = unsigned_type_for (type); }
>      (convert (rshift (lshift (convert:utype @0) @2) @3))))))
>
> +/* Fold ((type)(a<0)) << SIGNBITOFA into ((type)a) & signbit. */
> +(simplify
> + (lshift (convert (lt @0 integer_zerop@1)) INTEGER_CST@2)
> + (if (TYPE_SIGN (TREE_TYPE (@0)) == SIGNED
> +      && wi::eq_p (wi::to_wide (@2), TYPE_PRECISION (TREE_TYPE (@0)) - 1))
> +  (with { wide_int wone = wi::one (TYPE_PRECISION (type)); }
> +   (bit_and (convert @0)
> +            { wide_int_to_tree (type,
> +                               wi::lshift (wone, wi::to_wide (@2))); }))))
> +
>  /* Fold (-x >> C) into -(x > 0) where C = precision(type) - 1.  */
>  (for cst (INTEGER_CST VECTOR_CST)
>   (simplify
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c
> new file mode 100644
> index 00000000000..f086f073b38
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr103218-1.c
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* PR tree-optimization/103218 */
> +
> +/* These first two are removed during forwprop1 */
> +signed char f(signed char a)
> +{
> +  signed char t = a < 0;
> +  int tt = (unsigned char)(t << 7);
> +  return tt;
> +}
> +signed char f0(signed char a)
> +{
> +  unsigned char t = a < 0;
> +  int tt = (unsigned char)(t << 7);
> +  return tt;
> +}
> +
> +/* This one is removed during phiopt. */
> +signed char  f1(signed char a)
> +{
> +    if (a < 0)
> +      return 1u<<7;
> +    return 0;
> +}
> +
> +/* These three examples should remove "a < 0" by optimized. */
> +/* { dg-final { scan-tree-dump-times "< 0" 0 "optimized"} } */
> --
> 2.17.1
>