[PATCH] Fix gimplification of const var initialization from COND_EXPR (PR c++/80129)

Jakub Jelinek jakub@redhat.com
Wed Mar 22 08:36:00 GMT 2017


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



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