Re: [PATCH 2/2] Fix 101805: Simplify min/max of boolean arguments

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

On Sat, Aug 14, 2021 at 2:21 AM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> I noticed this while Richard B. fixing PR101756.
> Basically min of two bools is the same as doing an "and"
> and max of two bools is doing an "ior".

But that's only true for unsigned vals.  For signed ones it would
be the other way around and also restricted to 1-bit precision bools.
For signed bools the gimple_truth_valued_p check likely is wrong as well
unless 1-bit precision?  IIRC Ada has non-1 bit precision BOOLEAN_TYPE
nodes while fortran bools have 1-bit precision but different sizes.  The
vector bools are IIRC the only 'signed' bools we have and those have
precisions != 1.  I think we can use the fact that any non -1/0/1 value
in a N-bit precision bool invokes undefined behavior though.  But whether
in a N-bit signed precision bool the canonical true value is -1 or 1 isn't
as clear (maybe we can resort to TYPE_MIN/MAX_VALUE here, not sure).

Way out would be to restrict all this to TYPE_UNSIGNED BOOLEAN_TYPE
or non-BOOLEAN_TYPE?

Richard.

> gcc/ChangeLog:
>
>         * match.pd: Add min/max patterns for bool types.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/bool-12.c: New test.
> ---
>  gcc/match.pd                            | 10 +++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/bool-12.c | 27 +++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/bool-12.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index b1f2aaaac02..8fd60d08cfe 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -3103,6 +3103,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         && (GIMPLE || !TREE_SIDE_EFFECTS (@1)))
>     (cond (cmp @2 @3) @1 @0))))
>
> +/* max(bool0, bool1) -> bool0 | bool1 */
> +(simplify
> + (max gimple_truth_valued_p@0 gimple_truth_valued_p@1)
> + (bit_ior @0 @1))
> +
> +/* min(bool0, bool1) -> bool0 & bool1 */
> +(simplify
> + (min gimple_truth_valued_p@0 gimple_truth_valued_p@1)
> + (bit_and @0 @1))
> +
>  /* Simplifications of shift and rotates.  */
>
>  (for rotate (lrotate rrotate)
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bool-12.c b/gcc/testsuite/gcc.dg/tree-ssa/bool-12.c
> new file mode 100644
> index 00000000000..2d8ad9912d3
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/bool-12.c
> @@ -0,0 +1,27 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized -fdump-tree-original" } */
> +#define bool _Bool
> +int maxbool(bool ab, bool bb)
> +{
> +  int a = ab;
> +  int b = bb;
> +  int c;
> +  c = (a > b)?a : b;
> +  return c;
> +}
> +int minbool(bool ab, bool bb)
> +{
> +  int a = ab;
> +  int b = bb;
> +  int c;
> +  c = (a < b)?a : b;
> +  return c;
> +}
> +/* Original should have one of each MAX/MIN expressions. */
> +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "original" } */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "original"} } */
> +
> +/* By the time we reach optimized, the MAX and MIN expressions
> +   should have been removed. */
> +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "optimized"} } */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 0 "optimized"} } */
> --
> 2.27.0
>