[Bug tree-optimization/124358] [13/14/15/16 Regression] wrong code when accessing an pointer to array via pointer arithmetic since r12-6382

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124358

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:acf7028b79b72176f8ab2f6ebc4dbb9b5fb11a48

commit r16-7923-gacf7028b79b72176f8ab2f6ebc4dbb9b5fb11a48
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Mar 6 08:14:09 2026 +0100

    match.pd: Move cast into p+ operand for (ptr) (x p+ y) p+ z -> (ptr) (x p+
(y + z)) [PR124358]

    The following testcase is miscompiled since my r12-6382 change, because
    it doesn't play well with the gimple_fold_indirect_ref function which uses
    STRIP_NOPS and then has
      /* *(foo *)fooarrptr => (*fooarrptr)[0] */
      if (TREE_CODE (TREE_TYPE (subtype)) == ARRAY_TYPE
          && TREE_CODE (TYPE_SIZE (TREE_TYPE (TREE_TYPE (subtype)))) ==
INTEGER_CST
          && useless_type_conversion_p (type, TREE_TYPE (TREE_TYPE (subtype))))
        {
          tree type_domain;
          tree min_val = size_zero_node;
          tree osub = sub;
          sub = gimple_fold_indirect_ref (sub);
          if (! sub)
            sub = build1 (INDIRECT_REF, TREE_TYPE (subtype), osub);
          type_domain = TYPE_DOMAIN (TREE_TYPE (sub));
          if (type_domain && TYPE_MIN_VALUE (type_domain))
            min_val = TYPE_MIN_VALUE (type_domain);
          if (TREE_CODE (min_val) == INTEGER_CST)
            return build4 (ARRAY_REF, type, sub, min_val, NULL_TREE,
NULL_TREE);
        }
    Without the GENERIC
     #if GENERIC
     (simplify
       (pointer_plus (convert:s (pointer_plus:s @0 @1)) @3)
       (convert:type (pointer_plus @0 (plus @1 @3))))
     #endif
    we have INDIRECT_REF of POINTER_PLUS_EXPR with int * type of NOP_EXPR
    to that type of POINTER_PLUS_EXPR with pointer to int[4] ARRAY_TYPE, so
    gimple_fold_indirect_ref doesn't create the ARRAY_REF.
    But with it, it is simplified to NOP_EXPR to int * type from
    POINTER_PLUS_EXPR with pointer to int[4] ARRAY_TYPE, the NOP_EXPR is
    skipped over by STRIP_NOPS and the above code triggers.

    The following patch fixes it by swapping the order, do NOP_EXPR
    inside of POINTER_PLUS_EXPR first argument instead of NOP_EXPR with
    POINTER_PLUS_EXPR.

    2026-03-06  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/124358
            * match.pd ((ptr) (x p+ y) p+ z -> (ptr) (x p+ (y + z))): Simplify
            into (ptr) x p+ (y + z) instead.

            * gcc.c-torture/execute/pr124358.c: New test.