Re: [PATCH] Allow relayout_decl on FIELD_DECLs (PR c/72816)

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Aug 08, 2016 at 11:04:32AM +0000, Joseph Myers wrote:
> On Sat, 6 Aug 2016, Jakub Jelinek wrote:
> 
> > --- gcc/testsuite/gcc.dg/pr72816.c.jj	2016-08-06 13:06:45.046003282 +0200
> > +++ gcc/testsuite/gcc.dg/pr72816.c	2016-08-06 13:07:57.217093845 +0200
> > @@ -0,0 +1,9 @@
> > +/* PR c/72816 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-std=gnu11" } */
> > +
> > +typedef const int A[];
> > +struct S {
> > +  int a;
> > +  A b;	/* { dg-error "array size missing" } */
> > +};
> 
> As far as I can tell, this is actually valid code that should not produce 
> an error; the type of a flexible array member can be given by a typedef, 
> and I see nothing to disallow it being given by a typedef for an array of 
> qualified type.  Note that both the version of this test without const, 
> and the version with const but not using a typedef, are accepted.

Indeed.
The following untested patch fixes the issue for me.  The problem was that
when we create the distinct type with TYPE_DOMAIN [0:], if
TYPE_MAIN_VARIANT (orig_qual_type) is TYPE_MAIN_VARIANT (type) before we
do this, then c_build_qualified_type will return that orig_qual_type and
the TYPE_DOMAIN [0:] is gone again.  I think for orig_qual_indirect > 0
we are ok, in that case c_build_qualified_type will never return that and
as the flexible array member is the outermost ARRAY_TYPE, we should be fine.
But perhaps if (orig_qual_indirect > 0 && orig_qual_type), we never reach
the flexible array member through typedef else if, so perhaps
just unconditional orig_qual_type = NULL_TREE; in that else if would work too.
Which of these two versions do you prefer (or something else)?
Shall I revert the stor-layout.c change which might be unnecessary (though
shouldn't hurt)?

2016-08-10  Jakub Jelinek  <jakub@redhat.com>

	PR c/72816
	* c-decl.c (grokdeclarator): When adding TYPE_DOMAIN for flexible
	array member through typedef, for orig_qual_indirect == 0 clear
	orig_qual_type.

	* gcc.dg/pr72816.c: New test.

--- gcc/c/c-decl.c.jj	2016-08-06 12:11:47.000000000 +0200
+++ gcc/c/c-decl.c	2016-08-10 17:07:10.675144603 +0200
@@ -6710,6 +6710,8 @@ grokdeclarator (const struct c_declarato
 	    type = build_distinct_type_copy (TYPE_MAIN_VARIANT (type));
 	    TYPE_DOMAIN (type) = build_range_type (sizetype, size_zero_node,
 						   NULL_TREE);
+	    if (orig_qual_indirect == 0)
+	      orig_qual_type = NULL_TREE;
 	  }
 	type = c_build_qualified_type (type, type_quals, orig_qual_type,
 				       orig_qual_indirect);
--- gcc/testsuite/gcc.dg/pr72816.c.jj	2016-08-07 11:48:34.000000000 +0200
+++ gcc/testsuite/gcc.dg/pr72816.c	2016-08-10 17:08:21.153266419 +0200
@@ -5,5 +5,5 @@
 typedef const int A[];
 struct S {
   int a;
-  A b;	/* { dg-error "array size missing" } */
+  A b;
 };


	Jakub