[Bug middle-end/58564] [4.7/4.8/4.9 Regression] possible wrong code bug at -O0

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58564

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
          Component|c                           |middle-end
   Target Milestone|---                         |4.7.4
            Summary|possible wrong code bug at  |[4.7/4.8/4.9 Regression]
                   |-O0                         |possible wrong code bug at
                   |                            |-O0

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the bug is in the
      /* A < 0 ? <sign bit of A> : 0 is simply (A & <sign bit of A>).  */
      if (TREE_CODE (arg0) == LT_EXPR
          && integer_zerop (TREE_OPERAND (arg0, 1))
          && integer_zerop (op2)
          && (tem = sign_bit_p (TREE_OPERAND (arg0, 0), arg1)))
...
transformation in fold_ternary_loc or sign_bit_p or combination thereof.
We get here with arg0 ((int) (d == &c && a != 1)) < 0, arg1 1U and arg2 0U,
sign_bit_p (surprisingly) looks through zero extensions (of bool to int)
and returns (d == &c && a != 1) and we incorrectly fold it as
(d == &c && a != 1) & 1.