PR c++/92009 - ICE with punning of typeid.

There were two issues in this PR:

1) We were crashing in is_really_empty_class because we say that the
internal RTTI types are classes, but never gave them TYPE_BINFO.

2) We were allowing the cast to a different pointer type because STRIP_NOPS
in cxx_fold_indirect_ref ignored REINTERPRET_CAST_P.

	* rtti.c (get_tinfo_desc): Call xref_basetypes.
	* constexpr.c (cxx_fold_indirect_ref): Don't strip
	REINTERPRET_CAST_P.

gcc/cp/ChangeLog

+2020-01-14  Jason Merrill  <jason@redhat.com>
+
+	PR c++/92009 - ICE with punning of typeid.
+	* rtti.c (get_tinfo_desc): Call xref_basetypes.
+	* constexpr.c (cxx_fold_indirect_ref): Don't strip
+	REINTERPRET_CAST_P.
+
 2020-01-13  Jason Merrill  <jason@redhat.com>
 
 	PR c++/92746 - ICE with noexcept of function concept check.

gcc/cp/constexpr.c

@@ -4023,7 +4023,16 @@ cxx_fold_indirect_ref (location_t loc, tree type, tree op0, bool *empty_base)
   tree subtype;
   poly_uint64 const_op01;
 
-  STRIP_NOPS (sub);
+  /* STRIP_NOPS, but stop if REINTERPRET_CAST_P.  */
+  while (CONVERT_EXPR_P (sub) || TREE_CODE (sub) == NON_LVALUE_EXPR
+	 || TREE_CODE (sub) == VIEW_CONVERT_EXPR)
+    {
+      if (TREE_CODE (sub) == NOP_EXPR
+	  && REINTERPRET_CAST_P (sub))
+	return NULL_TREE;
+      sub = TREE_OPERAND (sub, 0);
+    }
+
   subtype = TREE_TYPE (sub);
   if (!INDIRECT_TYPE_P (subtype))
     return NULL_TREE;

gcc/cp/rtti.c

@@ -1472,6 +1472,7 @@ get_tinfo_desc (unsigned ix)
   /* Pass the fields chained in reverse.  */
   finish_builtin_struct (pseudo_type, pseudo_name, fields, NULL_TREE);
   CLASSTYPE_AS_BASE (pseudo_type) = pseudo_type;
+  xref_basetypes (pseudo_type, /*bases=*/NULL_TREE);
 
   res->type = cp_build_qualified_type (pseudo_type, TYPE_QUAL_CONST);
   res->name = get_identifier (real_name);

gcc/testsuite/g++.dg/cpp0x/constexpr-reinterpret2.C

+// { dg-do compile { target c++11 } }
+
+struct S { void *p; };
+struct T { S s; };
+constexpr S s = { nullptr };
+constexpr T t = { { nullptr } };
+
+constexpr void *
+foo ()
+{
+  return ((void **) &t)[0];	// { dg-error "reinterpret_cast" }
+}
+
+constexpr void *
+bar ()
+{
+  return ((void **) &s)[0];	// { dg-error "reinterpret_cast" }
+}
+
+constexpr auto x = foo ();
+constexpr auto y = bar ();

gcc/testsuite/g++.dg/rtti/typeid13.C

+// PR c++/92009
+
+namespace std {
+  class type_info {};
+}
+
+bool
+a2 ()
+{
+  return ((void **) &typeid (int))[0];
+}