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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/56961] stack overflow in gimplifier with volatile field
Date: Thu, 05 Jun 2014 12:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56961

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #8)
> (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.

The following should preserve those.

Index: gcc/cp/cp-gimplify.c
===================================================================
--- gcc/cp/cp-gimplify.c        (revision 211262)
+++ gcc/cp/cp-gimplify.c        (working copy)
@@ -629,18 +629,14 @@ 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)))
+           if (!TREE_SIDE_EFFECTS (op1))
              *expr_p = op0;
-           else if (TREE_CODE (op1) == MEM_REF
-                    && TREE_THIS_VOLATILE (op1))
+           else if (TREE_THIS_VOLATILE (op1)
+                    && (REFERENCE_CLASS_P (op1) || DECL_P (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);
+               *expr_p = build2 (COMPOUND_EXPR, TREE_TYPE (*expr_p),
+                                 op0, build_fold_addr_expr (op1));
+
              }
            else
              *expr_p = build2 (COMPOUND_EXPR, TREE_TYPE (*expr_p),