Re: [PATCH] ssa_name_has_boolean_range vs signed-boolean:31 types

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

On Sat, Sep 2, 2023 at 4:33 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This turns out to be a latent bug in ssa_name_has_boolean_range
> where it would return true for all boolean types but all of the
> uses of ssa_name_has_boolean_range was expecting 0/1 as the range
> rather than [-1,0].
> So when I fixed vector lower to do all comparisons in boolean_type
> rather than still in the signed-boolean:31 type (to fix a different issue),
> the pattern in match for `-(type)!A -> (type)A - 1.` would assume A (which
> was signed-boolean:31) had a range of [0,1] which broke down and sometimes
> gave us -1/-2 as values rather than what we were expecting of -1/0.
>
> This was the simpliest patch I found while testing.
>
> We have another way of matching [0,1] range which we could use instead
> of ssa_name_has_boolean_range except that uses only the global ranges
> rather than the local range (during VRP).
> I tried to clean this up slightly by using gimple_match_zero_one_valuedp
> inside ssa_name_has_boolean_range but that failed because due to using
> only the global ranges. I then tried to change get_nonzero_bits to use
> the local ranges at the optimization time but that failed also because
> we would remove branches to __builtin_unreachable during evrp and lose
> information as we don't set the global ranges during evrp.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu.

I guess the name of 'ssa_name_has_boolean_range' is unfortunate here.

We also lack documenting BOOLEAN_TYPE with [-1,0], neither tree.def
nor generic.texi elaborate on those.  build_nonstandard_boolean_type
simply calls fixup_signed_type which will end up setting MIN/MAX value
to [INT_MIN, INT_MAX].

Iff ssa_name_has_boolean_range really checks for zero_one we should
maybe rename it.

Iff _all_ signed BOOLEAN_TYPE have a true value of -1 (signed:8 can
very well represent [0, 1] as well) then we should document that.  (No,
I don't think we want TYPE_MIN/MAX_VALUE to specify this)

At some point the middle-end was very conservative and only considered
unsigned BOOLEAN_TYPE with 1 bit precision to have a [0,1] range.

I think that a more general 'boolean range' (not [0, 1]) query is only
possible if we hand in context.

The patch is definitely correct - not all BOOLEAN_TYPE types have a [0, 1]
range, thus OK.

Does Ada have signed booleans that are BOOLEAN_TYPE but do _not_
have [-1, 0] as range?  I think documenting [0, 1] for (single-bit precision?)
unsigned BOOLEAN_TYPE and [-1, 1] for signed BOOLEAN_TYPE would
be conservative.

Thanks,
Richard.

>         PR 110817
>
> gcc/ChangeLog:
>
>         * tree-ssanames.cc (ssa_name_has_boolean_range): Remove the
>         check for boolean type as they don't have "[0,1]" range.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.c-torture/execute/pr110817-1.c: New test.
>         * gcc.c-torture/execute/pr110817-2.c: New test.
>         * gcc.c-torture/execute/pr110817-3.c: New test.
> ---
>  gcc/testsuite/gcc.c-torture/execute/pr110817-1.c | 13 +++++++++++++
>  gcc/testsuite/gcc.c-torture/execute/pr110817-2.c | 16 ++++++++++++++++
>  gcc/testsuite/gcc.c-torture/execute/pr110817-3.c | 14 ++++++++++++++
>  gcc/tree-ssanames.cc                             |  4 ----
>  4 files changed, 43 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr110817-1.c
>  create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr110817-2.c
>  create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr110817-3.c
>
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr110817-1.c b/gcc/testsuite/gcc.c-torture/execute/pr110817-1.c
> new file mode 100644
> index 00000000000..1d33fa9a207
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr110817-1.c
> @@ -0,0 +1,13 @@
> +typedef unsigned long __attribute__((__vector_size__ (8))) V;
> +
> +
> +V c;
> +
> +int
> +main (void)
> +{
> +  V v = ~((V) { } <=0);
> +  if (v[0])
> +    __builtin_abort ();
> +  return 0;
> +}
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr110817-2.c b/gcc/testsuite/gcc.c-torture/execute/pr110817-2.c
> new file mode 100644
> index 00000000000..1f759178425
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr110817-2.c
> @@ -0,0 +1,16 @@
> +
> +typedef unsigned char u8;
> +typedef unsigned __attribute__((__vector_size__ (8))) V;
> +
> +V v;
> +unsigned char c;
> +
> +int
> +main (void)
> +{
> +  V x = (v > 0) > (v != c);
> + // V x = foo ();
> +  if (x[0] || x[1])
> +    __builtin_abort ();
> +  return 0;
> +}
> diff --git a/gcc/testsuite/gcc.c-torture/execute/pr110817-3.c b/gcc/testsuite/gcc.c-torture/execute/pr110817-3.c
> new file mode 100644
> index 00000000000..36f09c88dd9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/execute/pr110817-3.c
> @@ -0,0 +1,14 @@
> +typedef unsigned __attribute__((__vector_size__ (1*sizeof(unsigned)))) V;
> +
> +V v;
> +unsigned char c;
> +
> +int
> +main (void)
> +{
> +  V x = (v > 0) > (v != c);
> +  volatile signed int t = x[0];
> +  if (t)
> +    __builtin_abort ();
> +  return 0;
> +}
> diff --git a/gcc/tree-ssanames.cc b/gcc/tree-ssanames.cc
> index 23387b90fe3..6c362995c1a 100644
> --- a/gcc/tree-ssanames.cc
> +++ b/gcc/tree-ssanames.cc
> @@ -521,10 +521,6 @@ ssa_name_has_boolean_range (tree op)
>  {
>    gcc_assert (TREE_CODE (op) == SSA_NAME);
>
> -  /* Boolean types always have a range [0..1].  */
> -  if (TREE_CODE (TREE_TYPE (op)) == BOOLEAN_TYPE)
> -    return true;
> -
>    /* An integral type with a single bit of precision.  */
>    if (INTEGRAL_TYPE_P (TREE_TYPE (op))
>        && TYPE_UNSIGNED (TREE_TYPE (op))
> --
> 2.31.1
>