On Sun, Sep 17, 2023 at 11:41 PM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> So it turns out VN can't handle any kind of recusion for match. In this
> case we have `b = a & -1` and we try to match a as being zero_one_valued_p
> and VN returns b as being the value and we just go into an infinite loop at
> this point.
Huh, interesting. Must be because we return an available expression for
the b, a & -1 equivalency class. Otherwise I'd have expected you get 'a'.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
OK.
Richard.
> Note genmatch should warn (or error out) if this gets detected so I filed PR
> 111446
> which I will be looking into next week or the week after so we don't run into
> this issue again.
>
> PR tree-optimization/111442
>
> gcc/ChangeLog:
>
> * match.pd (zero_one_valued_p): Have the bit_and match not be
> recusive.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.c-torture/compile/pr111442-1.c: New test.
> ---
> gcc/match.pd | 5 ++++-
> gcc/testsuite/gcc.c-torture/compile/pr111442-1.c | 13 +++++++++++++
> 2 files changed, 17 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr111442-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 887665633d4..773c3810f51 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -2183,8 +2183,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>
> /* (a&1) is always [0,1] too. This is useful again when
> the range is not known. */
> +/* Note this can't be recusive due to VN handling of equivalents,
> + VN and would cause an infinite recusion. */
> (match zero_one_valued_p
> - (bit_and:c@0 @1 zero_one_valued_p))
> + (bit_and:c@0 @1 integer_onep)
> + (if (INTEGRAL_TYPE_P (type))))
>
> /* A conversion from an zero_one_valued_p is still a [0,1].
> This is useful when the range of a variable is not known */
> diff --git a/gcc/testsuite/gcc.c-torture/compile/pr111442-1.c
> b/gcc/testsuite/gcc.c-torture/compile/pr111442-1.c
> new file mode 100644
> index 00000000000..5814ee938de
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/pr111442-1.c
> @@ -0,0 +1,13 @@
> +
> +int *a, b;
> +int main() {
> + int d = 1, e;
> + if (d)
> + e = a ? 0 % 0 : 0;
> + if (d)
> + a = &d;
> + d = -1;
> + b = d & e;
> + b = 2 * e ^ 1;
> + return 0;
> +}
> --
> 2.31.1
>
