Re: RFC: g++ aliasing (was: Re: g++ and aliasing bools)

[Dan Nicolaescu <dann at godzilla dot ICS dot UCI dot EDU>]

Mark Mitchell <mark@codesourcery.com> writes:

  > > +           if (TYPE_USES_VIRTUAL_BASECLASSES (t))
  > > +             return false;
  > 
  > You need to recursively check non-virtual base classes, too, don't you?

Yep. It's needed when one of the base classes has a member that has an
abstract base.

Updated patch with all your other comments incorporated below. 
Plus I added an abort for sanity checking. 

        C++ alias analysis improvement. 
	* alias.c (record_component_aliases): Record aliases for base 
        classes too.
	* cp/cp-lang.c (ok_to_generate_alias_set_for_type): New function.
	(cxx_get_alias_set): Use it.


*** alias.c.~1.166.~	Tue Mar  5 23:56:32 2002
--- alias.c	Tue Mar  5 23:57:14 2002
***************
*** 679,684 ****
--- 679,694 ----
      case RECORD_TYPE:
      case UNION_TYPE:
      case QUAL_UNION_TYPE:
+       /* Recursively record aliases for the base classes, if there are any */
+       if (TYPE_BINFO (type) != NULL && TYPE_BINFO_BASETYPES (type) != NULL)
+         {
+           int i;
+           for (i = 0; i < TREE_VEC_LENGTH (TYPE_BINFO_BASETYPES (type)); i++)
+             {
+               tree binfo = TREE_VEC_ELT (TYPE_BINFO_BASETYPES (type), i);
+               record_alias_subset (superset, get_alias_set (BINFO_TYPE (binfo)));
+             }
+         }
        for (field = TYPE_FIELDS (type); field != 0; field = TREE_CHAIN (field))
  	if (TREE_CODE (field) == FIELD_DECL && ! DECL_NONADDRESSABLE_P (field))
  	  record_alias_subset (superset, get_alias_set (TREE_TYPE (field)));

Index: cp-lang.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cp/cp-lang.c,v
retrieving revision 1.10
diff -c -3 -p -c -r1.10 cp-lang.c
*** cp-lang.c	2002/02/28 07:39:37	1.10
--- cp-lang.c	2002/03/07 00:21:04
*************** static HOST_WIDE_INT cxx_get_alias_set P
*** 97,112 ****
  /* Each front end provides its own hooks, for toplev.c.  */
  const struct lang_hooks lang_hooks = LANG_HOOKS_INITIALIZER;
  
  /* Special routine to get the alias set for C++.  */
  
  static HOST_WIDE_INT
  cxx_get_alias_set (t)
       tree t;
  {
!   /* It's not yet safe to use alias sets for classes in C++ because
!      the TYPE_FIELDs list for a class doesn't mention base classes.  */
!   if (AGGREGATE_TYPE_P (t))
      return 0;
! 
    return c_common_get_alias_set (t);
  }
--- 97,205 ----
  /* Each front end provides its own hooks, for toplev.c.  */
  const struct lang_hooks lang_hooks = LANG_HOOKS_INITIALIZER;
  
+ /* Check if a C++ type is safe for aliasing.
+    Return TRUE if T safe for aliasing FALSE otherwise.  */
+ 
+ static bool
+ ok_to_generate_alias_set_for_type (t)
+      tree t;
+ {
+   if (AGGREGATE_TYPE_P (t))
+     {
+       if ((TREE_CODE (t) == RECORD_TYPE) || (TREE_CODE (t) == UNION_TYPE))
+         {
+           tree fields;
+           /* PODs are safe.  */
+           if (! CLASSTYPE_NON_POD_P(t))
+             return true;
+           /* Classes with virtual baseclasses are not.  */
+           if (TYPE_USES_VIRTUAL_BASECLASSES (t))
+             return false;
+           /* Recursively check the base classes.  */
+           if (TYPE_BINFO (t) != NULL && TYPE_BINFO_BASETYPES (t) != NULL)
+             {
+               int i;
+               for (i = 0; i < TREE_VEC_LENGTH (TYPE_BINFO_BASETYPES (t)); i++)
+                 {
+                   tree binfo = TREE_VEC_ELT (TYPE_BINFO_BASETYPES (t), i);
+                   if (!ok_to_generate_alias_set_for_type (BINFO_TYPE (binfo)))
+                     return false;
+                 }
+             }
+           /* Check all the fields.  */
+           for (fields = TYPE_FIELDS (t); fields; fields = TREE_CHAIN (fields))
+             {
+               if (TREE_CODE (fields) != FIELD_DECL)
+                 continue;
+               if (! ok_to_generate_alias_set_for_type (TREE_TYPE (fields)))
+                 return false;
+             }
+           return true;
+         }
+       else if (TREE_CODE (t) == ARRAY_TYPE)
+         return ok_to_generate_alias_set_for_type (TREE_TYPE (t));
+       else
+         /* This should never happen, we dealt with all the aggregate
+            types that can appear in C++ abover.  */
+         abort ();
+     }
+   else
+     return true;
+ }
+ 
  /* Special routine to get the alias set for C++.  */
  
  static HOST_WIDE_INT
  cxx_get_alias_set (t)
       tree t;
  {
!   /* It's not yet safe to use alias sets for some classes in C++ */
!   if (!ok_to_generate_alias_set_for_type(t))
      return 0;
!   
    return c_common_get_alias_set (t);
  }