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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/56961] stack overflow in gimplifier with volatile field
Date: Thu, 05 Jun 2014 12:35:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56961

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #7)
> I suggest
> 
> Index: gcc/cp/cp-gimplify.c
> ===================================================================
> --- gcc/cp/cp-gimplify.c        (revision 211262)
> +++ gcc/cp/cp-gimplify.c        (working copy)
> @@ -630,18 +630,8 @@ cp_gimplify_expr (tree *expr_p, gimple_s
>                Also drop volatile variables on the RHS to avoid infinite
>                recursion from gimplify_expr trying to load the value.  */
>             if (!TREE_SIDE_EFFECTS (op1)
> -               || (DECL_P (op1) && TREE_THIS_VOLATILE (op1)))
> +               || TREE_THIS_VOLATILE (op1))
>               *expr_p = op0;
> -           else if (TREE_CODE (op1) == MEM_REF
> -                    && TREE_THIS_VOLATILE (op1))
> -             {
> -               /* Similarly for volatile MEM_REFs on the RHS.  */
> -               if (!TREE_SIDE_EFFECTS (TREE_OPERAND (op1, 0)))
> -                 *expr_p = op0;
> -               else
> -                 *expr_p = build2 (COMPOUND_EXPR, TREE_TYPE (*expr_p),
> -                                   TREE_OPERAND (op1, 0), op0);
> -             }
>             else
>               *expr_p = build2 (COMPOUND_EXPR, TREE_TYPE (*expr_p),
>                                 op0, op1);

This might of course drop arbitrary side-effects of op1 such as
a volatile load from a.b[foo()] where foo () would be dropped.

So it isn't really correct.