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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106617] [13 Regression] gcc is very slow at
 ternary expressions,
Date: Mon, 15 Aug 2022 09:06:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106617

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
We don't fold because

    case COMPOUND_EXPR:
      /* When pedantic, a compound expression can be neither an lvalue
         nor an integer constant expression.  */
      if (TREE_SIDE_EFFECTS (arg0) || TREE_CONSTANT (arg1))
        return NULL_TREE;
      /* Don't let (0, 0) be null pointer constant.  */
      tem =3D integer_zerop (arg1) ? build1_loc (loc, NOP_EXPR, type, arg1)
                                 : fold_convert_loc (loc, type, arg1);
      return tem;

where we chicken out because of the fear of early folding.  At least the
C frontend should get this correct now.  Ideally the above would
just return arg1 if !TREE_SIDE_EFFECTS (arg0).  OTOH it's really sth for
language specific folding.

Of course the bug then would be still present when replacing (0, 0) with
something non-constant.=