[C++ PATCH] Fix aliasing warnings for typeid (PR c++/32260)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

-O2 -Wstrict-aliasing currently warns about many uses of typeid ().
THe problem is that the various artifical abi::__*info types have
abi::__type_info_pseudo rather than std::type_info as their first
field, although they really have the same layout.  So typeid casts
the address of say abi::__fundamental_type_info _ZTI* var to std::type_info *
and dereferences it, but the two have different alias sets and so
-Wstrict-aliasing warns.  We can't use std::type_info as the first
field of the derived types, as it is not a builtin type and we rely
on <typeinfo> to define it, but we surely can use the same alias
set for std::type_info and abi::__type_info_pseudo (and therefore
aliasing will be ok even for all the "derived" types, as they have
abi::__type_info_pseudo as the first field).  Nothing ever needs
to create alias sets for the abi::__* types before
{build,get}_typeid is called or emit_tinfo_decl is called
(they are touched only during the initialization otherwise).
{build,get}_typeid in typeid_ok_p ensure <typeinfo> has been included
(std::type_info is complete) and we can there copy the alias set
of std::type_info to abi:__fundamental_type_info when we call it the first
time.  emit_tinfo_decl is only called at the end and if there were no
typeids parsed, the alias set really doesn't matter.

Ok for trunk?

2007-11-01  Jakub Jelinek  <jakub@redhat.com>

	PR c++/32260
	* rtti.c (enum_tinfo_kind): Fix TK_TYPE_INFO_TYPE comment.
	(typeid_ok_p): Use the same alias set for abi::__type_info_pseudo
	as for std::type_info.

	* g++.dg/rtti/typeid7.C: New test.

--- gcc/cp/rtti.c.jj	2007-09-07 10:29:32.000000000 +0200
+++ gcc/cp/rtti.c	2007-11-01 12:55:34.000000000 +0100
@@ -79,7 +79,7 @@ DEF_VEC_ALLOC_O(tinfo_s,gc);
 
 typedef enum tinfo_kind
 {
-  TK_TYPE_INFO_TYPE,    /* std::type_info */
+  TK_TYPE_INFO_TYPE,    /* abi::__type_info_pseudo */
   TK_BASE_TYPE,		/* abi::__base_class_type_info */
   TK_BUILTIN_TYPE,	/* abi::__fundamental_type_info */
   TK_ARRAY_TYPE,	/* abi::__array_type_info */
@@ -264,6 +264,8 @@ get_tinfo_decl_dynamic (tree exp)
 static bool
 typeid_ok_p (void)
 {
+  tree pseudo_type_info;
+
   if (! flag_rtti)
     {
       error ("cannot use typeid with -fno-rtti");
@@ -276,6 +278,17 @@ typeid_ok_p (void)
       return false;
     }
 
+  pseudo_type_info
+    = VEC_index (tinfo_s, tinfo_descs, TK_TYPE_INFO_TYPE)->type;
+
+  /* Make sure abi::__type_info_pseudo has the same alias set
+     as std::type_info.  */
+  if (! TYPE_ALIAS_SET_KNOWN_P (pseudo_type_info))
+    {
+      tree type_info_type = TYPE_MAIN_VARIANT (const_type_info_type_node);
+      TYPE_ALIAS_SET (pseudo_type_info) = get_alias_set (type_info_type);
+    }
+
   return true;
 }
 
--- gcc/testsuite/g++.dg/rtti/typeid7.C.jj	2007-11-01 13:07:13.000000000 +0100
+++ gcc/testsuite/g++.dg/rtti/typeid7.C	2007-11-01 13:05:16.000000000 +0100
@@ -0,0 +1,61 @@
+// PR c++/32260
+// { dg-do compile }
+// { dg-options "-O2 -W -Wall" }
+
+#include <typeinfo>
+
+const std::type_info &
+f1 (int i)
+{
+  return typeid (i + 1);
+}
+
+const std::type_info &
+f2 ()
+{
+  return typeid (int);
+}
+
+struct A
+{
+  A ();
+  virtual ~A ();
+  void foo ();
+};
+
+const std::type_info &
+f3 ()
+{
+  return typeid (A);
+}
+
+const std::type_info &
+f4 (A *p)
+{
+  return typeid (*p);
+}
+
+const std::type_info &
+f5 ()
+{
+  return typeid (int *);
+}
+
+const std::type_info &
+f6 ()
+{
+  return typeid (int [26][12]);
+}
+
+const std::type_info &
+f7 ()
+{
+  return typeid (int [26][12]);
+}
+
+void (A::*pmr) ();
+const std::type_info &
+f8 ()
+{
+  return typeid (pmr);
+}

	Jakub