-fstrict-aliasing fixes 2/5: drop alias set 0 streaming

Hi,
this patch disables the streaming of alias 0 flag and adds a comment why.

Bootstrapped/regtested x86_64-linux, OK?

Honza

	* lto-streamer-out.c (hash_tree): Do not stream TYPE_ALIAS_SET.
	* tree-streamer-out.c (pack_ts_type_common_value_fields): Do not
	stream TYPE_ALIAS_SET.
	* tree-streamer-in.c (unpack_ts_type_common_value_fields): Do not
	stream TYPE_ALIAS_SET.

	* lto.c (compare_tree_sccs_1): Do not compare TYPE_ALIAS_SET.

On Tue, 1 Dec 2015, Jan Hubicka wrote:

> Hi,
> this patch disables the streaming of alias 0 flag and adds a comment why.
> 
> Bootstrapped/regtested x86_64-linux, OK?

Ok.

Thanks,
Richard.

> Honza
> 
> 	* lto-streamer-out.c (hash_tree): Do not stream TYPE_ALIAS_SET.
> 	* tree-streamer-out.c (pack_ts_type_common_value_fields): Do not
> 	stream TYPE_ALIAS_SET.
> 	* tree-streamer-in.c (unpack_ts_type_common_value_fields): Do not
> 	stream TYPE_ALIAS_SET.
> 
> 	* lto.c (compare_tree_sccs_1): Do not compare TYPE_ALIAS_SET.
> 
> Index: lto-streamer-out.c
> ===================================================================
> --- lto-streamer-out.c	(revision 231081)
> +++ lto-streamer-out.c	(working copy)
> @@ -1109,10 +1109,6 @@ hash_tree (struct streamer_tree_cache_d
>        hstate.commit_flag ();
>        hstate.add_int (TYPE_PRECISION (t));
>        hstate.add_int (TYPE_ALIGN (t));
> -      hstate.add_int ((TYPE_ALIAS_SET (t) == 0
> -					 || (!in_lto_p
> -					     && get_alias_set (t) == 0))
> -					? 0 : -1);
>      }
>  
>    if (CODE_CONTAINS_STRUCT (code, TS_TRANSLATION_UNIT_DECL))
> Index: lto/lto.c
> ===================================================================
> --- lto/lto.c	(revision 231081)
> +++ lto/lto.c	(working copy)
> @@ -1166,7 +1166,9 @@ compare_tree_sccs_1 (tree t1, tree t2, t
>        compare_values (TYPE_READONLY);
>        compare_values (TYPE_PRECISION);
>        compare_values (TYPE_ALIGN);
> -      compare_values (TYPE_ALIAS_SET);
> +      /* Do not compare TYPE_ALIAS_SET.  Doing so introduce ordering issues
> +         with calls to get_alias_set which may initialize it for streamed
> + 	 in types.  */
>      }
>  
>    /* We don't want to compare locations, so there is nothing do compare
> Index: tree-streamer-out.c
> ===================================================================
> --- tree-streamer-out.c	(revision 231081)
> +++ tree-streamer-out.c	(working copy)
> @@ -317,13 +317,9 @@ pack_ts_type_common_value_fields (struct
>    bp_pack_value (bp, TYPE_RESTRICT (expr), 1);
>    bp_pack_value (bp, TYPE_USER_ALIGN (expr), 1);
>    bp_pack_value (bp, TYPE_READONLY (expr), 1);
> -  /* Make sure to preserve the fact whether the frontend would assign
> -     alias-set zero to this type.  Do that only for main variants, because
> -     type variants alias sets are never computed.
> -     FIXME:  This does not work for pre-streamed builtin types.  */
> -  bp_pack_value (bp, (TYPE_ALIAS_SET (expr) == 0
> -		      || (!in_lto_p && TYPE_MAIN_VARIANT (expr) == expr
> -			  && get_alias_set (expr) == 0)), 1);
> +  /* We used to stream TYPE_ALIAS_SET == 0 information to let frontends mark
> +     types that are opaque for TBAA.  This however did not work as intended,
> +     becuase TYPE_ALIAS_SET == 0 was regularly lost in canonical type merging.  */
>    if (RECORD_OR_UNION_TYPE_P (expr))
>      {
>        bp_pack_value (bp, TYPE_TRANSPARENT_AGGR (expr), 1);
> Index: tree-streamer-in.c
> ===================================================================
> --- tree-streamer-in.c	(revision 231081)
> +++ tree-streamer-in.c	(working copy)
> @@ -366,7 +366,6 @@ unpack_ts_type_common_value_fields (stru
>    TYPE_RESTRICT (expr) = (unsigned) bp_unpack_value (bp, 1);
>    TYPE_USER_ALIGN (expr) = (unsigned) bp_unpack_value (bp, 1);
>    TYPE_READONLY (expr) = (unsigned) bp_unpack_value (bp, 1);
> -  TYPE_ALIAS_SET (expr) = bp_unpack_value (bp, 1) ? 0 : -1;
>    if (RECORD_OR_UNION_TYPE_P (expr))
>      {
>        TYPE_TRANSPARENT_AGGR (expr) = (unsigned) bp_unpack_value (bp, 1);
> 
>