re PR rtl-optimization/8634 (incorrect code for inlining of memcpy under -O2)

        PR opt/8634
        * explow.c (maybe_set_unchanging): Don't flag non-static const
        aggregate type initializers with RTX_UNCHANGING_P.

From-SVN: r65352

gcc/ChangeLog

+2003-04-07  Glen Nakamura  <glen@imodulo.com>
+
+	PR opt/8634
+	* explow.c (maybe_set_unchanging): Don't flag non-static const
+	aggregate type initializers with RTX_UNCHANGING_P.
+
 2003-04-07  Richard Henderson  <rth@redhat.com>
 
         PR opt/8634

gcc/explow.c

@@ -657,8 +657,18 @@ maybe_set_unchanging (ref, t)
   /* We can set RTX_UNCHANGING_P from TREE_READONLY for decls whose
      initialization is only executed once, or whose initializer always
      has the same value.  Currently we simplify this to PARM_DECLs in the
-     first case, and decls with TREE_CONSTANT initializers in the second.  */
+     first case, and decls with TREE_CONSTANT initializers in the second.
+
+     We cannot do this for non-static aggregates, because of the double
+     writes that can be generated by store_constructor, depending on the
+     contents of the initializer.  Yes, this does eliminate a good fraction
+     of the number of uses of RTX_UNCHANGING_P for a language like Ada.
+     It also eliminates a good quantity of bugs.  Let this be incentive to
+     eliminate RTX_UNCHANGING_P entirely in favour of a more reliable
+     solution, perhaps based on alias sets.  */
+
   if ((TREE_READONLY (t) && DECL_P (t)
+       && (TREE_STATIC (t) || ! AGGREGATE_TYPE_P (TREE_TYPE (t)))
        && (TREE_CODE (t) == PARM_DECL
 	   || (DECL_INITIAL (t) && TREE_CONSTANT (DECL_INITIAL (t)))))
       || TREE_CODE_CLASS (TREE_CODE (t)) == 'c')