Re: [PATCH] MATCH: Avoid recusive zero_one_valued_p for conversions

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

On Sun, Sep 17, 2023 at 3:45 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> So when VN finds a name which has a nop conversion, it says
> both names are equivalent to each other and the valuaization
> function for one will return the other. This normally does not
> cause any issues as there is no recusive matches. But after
> r14-4038-gb975c0dc3be285, there was one added. So we would
> do an infinite recusion on the match and never finish.
> This fixes the issue (and adds a comment in match.pd) by
> for converts just handle one level instead of being recusive
> always.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

> Note the testcase was reduced from tree-ssa-loop-niter.cc and then
> changed slightly into C rather than C++ but it still needs exceptions
> turned on get the IR that VN would produce this equivalence relationship
> going on. Also had to turn off early inline to force put to be inlined later.
>
>         PR tree-optimization/111435
>
> gcc/ChangeLog:
>
>         * match.pd (zero_one_valued_p): Don't do recusion
>         on converts.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.c-torture/compile/pr111435-1.c: New test.
> ---
>  gcc/match.pd                                   |  8 +++++++-
>  .../gcc.c-torture/compile/pr111435-1.c         | 18 ++++++++++++++++++
>  2 files changed, 25 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr111435-1.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 97405e6a5c3..887665633d4 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -2188,8 +2188,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>
>  /* 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 */
> +/* Note this matches can't be recusive because of the way VN handles
> +   nop conversions being equivalent and then recusive between them. */
>  (match zero_one_valued_p
> - (convert@0 zero_one_valued_p))
> + (convert@0 @1)
> + (if (INTEGRAL_TYPE_P (TREE_TYPE (@1))
> +      && (TYPE_UNSIGNED (TREE_TYPE (@1))
> +         || TYPE_PRECISION (TREE_TYPE (@1)) > 1)
> +      && wi::leu_p (tree_nonzero_bits (@1), 1))))
>
>  /* Transform { 0 or 1 } * { 0 or 1 } into { 0 or 1 } & { 0 or 1 }.  */
>  (simplify
> diff --git a/gcc/testsuite/gcc.c-torture/compile/pr111435-1.c b/gcc/testsuite/gcc.c-torture/compile/pr111435-1.c
> new file mode 100644
> index 00000000000..afa84dd59dd
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/pr111435-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-options "-fexceptions -fno-early-inlining" } */
> +/* { dg-require-effective-target exceptions } */
> +
> +void find_slot_with_hash(const int *);
> +
> +void put(const int *k, const int *) {
> +    find_slot_with_hash(k);
> +}
> +unsigned len();
> +int *address();
> +void h(int header, int **bounds) {
> +  if (!*bounds)
> +    return;
> +  unsigned t = *bounds ? len() : 0;
> +  int queue_index = t;
> +  address()[(unsigned)queue_index] = 0;
> +  put(&header, &queue_index);
> +}
> --
> 2.31.1
>