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

Richard Biener rguenther@suse.de
Wed Mar 22 08:59:00 GMT 2017


On Wed, 22 Mar 2017, Jakub Jelinek wrote:

> 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.

Ok.

> So, if you want, I can replace the DECL_P (result) check with VAR_P
> (result), and perhaps change the comment somehow.

Yeah, changing it to VAR_P and expanding the comment so it says
it avoids incorrect promotion to readonly-static.  (so it _is_
fishy that we have multiple assignments to TREE_READONLY objects
given that code looks at a single assignment only)

> > 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
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)



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