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Re: [PATCH] Fix gimplification of const var initialization from COND_EXPR (PR c++/80129)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Richard Biener <rguenther at suse dot de>
- Cc: Jason Merrill <jason at redhat dot com>, gcc-patches at gcc dot gnu dot org
- Date: Wed, 22 Mar 2017 09:36:48 +0100
- Subject: Re: [PATCH] Fix gimplification of const var initialization from COND_EXPR (PR c++/80129)
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- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Wed, Mar 22, 2017 at 09:20:32AM +0100, Richard Biener wrote:
> > --- gcc/gimplify.c.jj 2017-03-21 07:56:55.000000000 +0100
> > +++ gcc/gimplify.c 2017-03-21 13:37:45.555612652 +0100
> > @@ -5098,6 +5098,13 @@ gimplify_modify_expr_rhs (tree *expr_p,
> > if (ret != GS_ERROR)
> > ret = GS_OK;
> >
> > + /* If we are going to write RESULT more than once, clear
> > + TREE_READONLY flag, otherwise we might gimplify it
> > + incorrectly. */
> > + if (DECL_P (result)
>
> Can it ever be that result is sth like decl.component? At least I
> don't see GENERIC restricted in a way that it cannot. (and generally
> assigning to sth TREE_READONLY is fishy at best...)
I guess it can, but it can't trigger
if (valid_const_initializer
&& num_nonzero_elements > 1
&& TREE_READONLY (object)
&& VAR_P (object)
&& (flag_merge_constants >= 2 || !TREE_ADDRESSABLE (object)))
which is the problem here. The problem isn't multiple assignments to
TREE_READONLY object if it isn't promoted to static.
So, if you want, I can replace the DECL_P (result) check with VAR_P
(result), and perhaps change the comment somehow.
> I see how this fixes the problem at hand (and in a safe way), so the
> patch is probably ok, just looking how to avoid this situation in
> a more general (and better) way.
Jakub