[PATCH] stor-layout: Avoid DECL_BIT_FIELD_REPRESENTATIVE with NULL TREE_TYPE [PR101172]

[Richard Biener]

On Thu, 24 Jun 2021, Jakub Jelinek wrote:

> Hi!
> 
> finish_bitfield_representative has an early out if the field after a
> bitfield has error_mark_node type, but that early out leads to TREE_TYPE
> of the DECL_BIT_FIELD_REPRESENTATIVE being NULL, which breaks assumptions
> on code that uses the DECL_BIT_FIELD_REPRESENTATIVE during error-recovery.
> 
> The following patch instead sets TREE_TYPE of the representative to
> error_mark_node, something the users can deal with better.  At this point
> the representative can be set as DECL_BIT_FIELD_REPRESENTATIVE for multiple
> bitfields, so making sure that we clear the DECL_BIT_FIELD_REPRESENTATIVE
> instead would be harder (but doable, e.g. with the error_mark_node TREE_TYPE
> set by this patch set some flag in the caller and if the flag is there, walk
> all the fields once again and clear all DECL_BIT_FIELD_REPRESENTATIVE that
> have error_mark_node TREE_TYPE).
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

> 2021-06-24  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR middle-end/101172
> 	* stor-layout.c (finish_bitfield_representative): If nextf has
> 	error_mark_node type, set repr type to error_mark_node too.
> 
> 	* gcc.dg/pr101172.c: New test.
> 
> --- gcc/stor-layout.c.jj	2021-06-21 09:39:21.798485474 +0200
> +++ gcc/stor-layout.c	2021-06-23 11:10:22.617680051 +0200
> @@ -2086,7 +2086,10 @@ finish_bitfield_representative (tree rep
>        /* If there was an error, the field may be not laid out
>           correctly.  Don't bother to do anything.  */
>        if (TREE_TYPE (nextf) == error_mark_node)
> -	return;
> +	{
> +	  TREE_TYPE (repr) = error_mark_node;
> +	  return;
> +	}
>        maxsize = size_diffop (DECL_FIELD_OFFSET (nextf),
>  			     DECL_FIELD_OFFSET (repr));
>        if (tree_fits_uhwi_p (maxsize))
> --- gcc/testsuite/gcc.dg/pr101172.c.jj	2021-06-23 11:15:19.934670004 +0200
> +++ gcc/testsuite/gcc.dg/pr101172.c	2021-06-23 11:15:07.255841009 +0200
> @@ -0,0 +1,20 @@
> +/* PR middle-end/101172 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +union U
> +{
> +  int a[3];
> +  struct
> +  {
> +    int a : 3;
> +    struct this_struct var;	/* { dg-error "field 'var' has incomplete type" } */
> +  } b;
> +};
> +
> +const union U hello = {.a = {1, 2, 3}};
> +
> +void foo()
> +{
> +  int x = hello.b.a;
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)