re PR c++/13275 (Implementation of offsetof macro)

	PR c++/13275
	* c-common.h (enum rid): Add RID_OFFSETOF.
	* c-parser.in (rid_to_yy): Ignore RID_OFFSETOF.
	* ginclude/stddef.h (offsetof): Reimplement for C++, using
	__offsetof__.
	* doc/extend.texi: Document __offsetof__.

	PR c++/13275
	* lex.c (reswords): Add "__offsetof" and "__offsetof__".
	* parser.c (cp_parser): Add in_offsetof_p.
	(cp_parser_new): Initialize it.
	(cp_parser_primary_expression): Handle __offsetof__ (...).
	(cp_parser_postfix_expression): Allow casts to pointer type and
	uses of "->" in a constant expression if implementing offsetof.
	(cp_parser_unary_expression): Allow the use of "&" in a constant
	expression if implementing offsetof.

	PR c++/13275
	* g++.dg/other/offsetof2.C: Remove XFAIL.
	* g++.dg/parse/offsetof1.C: New test.
	* g++.gd/parse/offsetof2.C: Likewise.

From-SVN: r74702

12 files changed, 143 insertions, 35 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a9a86f312f7..6b0eee4d5bf 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2003-12-16  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/13275
+	* c-common.h (enum rid): Add RID_OFFSETOF.
+	* c-parser.in (rid_to_yy): Ignore RID_OFFSETOF.
+	* ginclude/stddef.h (offsetof): Reimplement for C++, using
+	__offsetof__.
+	* doc/extend.texi: Document __offsetof__.
+	
 2003-12-16  Stan Cox  <scox@redhat.com>
 
 	* config/iq2000/iq2000.h: Formatting.
diff --git a/gcc/c-common.h b/gcc/c-common.h
index 326fe519be4..28e8356004b 100644
--- a/gcc/c-common.h
+++ b/gcc/c-common.h
@@ -88,9 +88,10 @@ enum rid
   RID_PUBLIC,   RID_PRIVATE,  RID_PROTECTED,
   RID_TEMPLATE, RID_NULL,     RID_CATCH,
   RID_DELETE,   RID_FALSE,    RID_NAMESPACE,
-  RID_NEW,      RID_OPERATOR, RID_THIS,
-  RID_THROW,    RID_TRUE,     RID_TRY,
-  RID_TYPENAME, RID_TYPEID,   RID_USING,
+  RID_NEW,      RID_OFFSETOF, RID_OPERATOR, 
+  RID_THIS,     RID_THROW,    RID_TRUE,     
+  RID_TRY,      RID_TYPENAME, RID_TYPEID,   
+  RID_USING,
 
   /* casts */
   RID_CONSTCAST, RID_DYNCAST, RID_REINTCAST, RID_STATCAST,
diff --git a/gcc/c-parse.in b/gcc/c-parse.in
index b36ab06524a..954c37067ff 100644
--- a/gcc/c-parse.in
+++ b/gcc/c-parse.in
@@ -3484,6 +3484,7 @@ static const short rid_to_yy[RID_MAX] =
   /* RID_FALSE */	0,
   /* RID_NAMESPACE */	0,
   /* RID_NEW */		0,
+  /* RID_OFFSETOF */    0,
   /* RID_OPERATOR */	0,
   /* RID_THIS */	0,
   /* RID_THROW */	0,
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 4a19573adf6..31876c98145 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,21 @@
+2003-12-16  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/13275
+	* lex.c (reswords): Add "__offsetof" and "__offsetof__".
+	* parser.c (cp_parser): Add in_offsetof_p.
+	(cp_parser_new): Initialize it.
+	(cp_parser_primary_expression): Handle __offsetof__ (...).
+	(cp_parser_postfix_expression): Allow casts to pointer type and
+	uses of "->" in a constant expression if implementing offsetof.
+	(cp_parser_unary_expression): Allow the use of "&" in a constant
+	expression if implementing offsetof.
+
+2003-12-16  Giovanni Bajo  <giovannibajo@gcc.gnu.org>

+

+	PR c++/2294

+	* name-lookup.c (push_overloaded_decl): always construct an OVERLOAD

+	if the declaration comes from an using declaration.

+
 2003-12-16  Giovanni Bajo  <giovannibajo@gcc.gnu.org>
 
 	* semantics.c (finish_id_expression): Refactor the code to handle
@@ -17385,7 +17403,7 @@
 	* parse.y (member_init): Just pass in the type.
 	* init.c (expand_member_init): Handle getting a type.
 
-2000-07-04  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-07-04  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 	    Jason Merrill  <jason@redhat.com>
 
 	* decl.c (finish_function): Warn if a function has no return
@@ -17731,7 +17749,7 @@
 	* decl.c (pushdecl): Don't set DECL_CONTEXT from current_namespace.
 	(push_namespace): Set DECL_CONTEXT for a new NAMESPACE_DECL.
 
-2000-06-24  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-06-24  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* parse.y (complex_direct_notype_declarator): Support global_scope.
 	* Makefile.in: Adjust conflict count.
@@ -18916,7 +18934,7 @@
 	* semantics.c (finish_member_declaration): Don't mark members of
 	classes declared in an extern "C" region as extern "C".
 
-2000-05-22  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-05-22  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* decl2.c (qualified_lookup_using_namespace): Look through
 	namespace aliases.
@@ -19370,7 +19388,7 @@
 
 	* ir.texi: Correct typo.
 
-2000-04-25  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-04-25  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* decl.c (grokdeclarator): Reject VLAs as members.
 
@@ -19669,7 +19687,7 @@
 	(interface_only): Don't declare.
 	(interface_unknown): Likewise.
 
-2000-04-11  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-04-11  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* tree.h (HAVE_TEMPLATES): Remove definition.
 	* lang-options.h (-fthis-is-variable): Remove documentation.
@@ -19724,7 +19742,7 @@
 	(__pointer_to_member_type_info::__do_catch): Remove.
 	(__pointer_to_member_type_info::__pointer_catch): Implement.
 
-2000-04-10  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-04-10  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* lex.c (init_parse): Remove traces of classof and headof.
 	* decl2.c (flag_operator_names): Default to 1.
@@ -20437,7 +20455,7 @@ Wed Apr  5 15:12:18 MET DST 2000  Jan Hubicka  <jh@suse.cz>
 	* init.c (build_offset_ref): Handle the case of a templated member
 	function.
 
-2000-03-19  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-03-19  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* except.c (expand_exception_blocks): Clear catch_clauses_last.
 
@@ -20463,7 +20481,7 @@ Wed Apr  5 15:12:18 MET DST 2000  Jan Hubicka  <jh@suse.cz>
 	(layout_class_type): Implement new ABI handling of bitfields
 	longer than their types.
 
-2000-03-18  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-03-18  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* parse.y (extdefs): Call ggc_collect.
 	* parse.c: Regenerated.
@@ -21073,7 +21091,7 @@ Wed Apr  5 15:12:18 MET DST 2000  Jan Hubicka  <jh@suse.cz>
 
 	* decl.c (decls_match): Remove obsolete static member nadgering.
 
-2000-02-21  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-02-21  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* decl.c (grokdeclarator): Change ANSI to ISO.
 	* lex.c (consume_string, readescape, do_identifier): Likewise.
@@ -22100,7 +22118,7 @@ Wed Apr  5 15:12:18 MET DST 2000  Jan Hubicka  <jh@suse.cz>
 	* optimize.c (copy_body_r): Clear the operand three of a
 	TARGET_EXPR when copying it.
 
-2000-01-14  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-01-14  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* method.c (build_decl_overload_real): Check whether we are in ::
 	before returning __builtin_new/delete.
@@ -22397,6 +22415,6 @@ Wed Apr  5 15:12:18 MET DST 2000  Jan Hubicka  <jh@suse.cz>
 	(fixup_vtable_deltas1): Likewise.
 	(finish_struct_1): Likewise.
 
-2000-01-01  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
+2000-01-01  Martin v. Löwis  <loewis@informatik.hu-berlin.de>
 
 	* call.c (build_new_method_call): Also check destructors.
diff --git a/gcc/cp/lex.c b/gcc/cp/lex.c
index 37baa485ce9..50af1178470 100644
--- a/gcc/cp/lex.c
+++ b/gcc/cp/lex.c
@@ -266,6 +266,8 @@ static const struct resword reswords[] =
   { "__inline__",	RID_INLINE,	0 },
   { "__label__",	RID_LABEL,	0 },
   { "__null",		RID_NULL,	0 },
+  { "__offsetof",       RID_OFFSETOF,   0 },
+  { "__offsetof__",     RID_OFFSETOF,   0 },
   { "__real",		RID_REALPART,	0 },
   { "__real__",		RID_REALPART,	0 },
   { "__restrict",	RID_RESTRICT,	0 },
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 14923b17ce4..89806116055 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -1230,6 +1230,9 @@ typedef struct cp_parser GTY(())
      been seen that makes the expression non-constant.  */
   bool non_constant_expression_p;
 
+  /* TRUE if we are parsing the argument to "__offsetof__".  */
+  bool in_offsetof_p;
+
   /* TRUE if local variable names and `this' are forbidden in the
      current context.  */
   bool local_variables_forbidden_p;
@@ -2225,6 +2228,9 @@ cp_parser_new (void)
   parser->allow_non_constant_expression_p = false;
   parser->non_constant_expression_p = false;
 
+  /* We are not parsing offsetof.  */
+  parser->in_offsetof_p = false;
+
   /* Local variable names are not forbidden.  */
   parser->local_variables_forbidden_p = false;
 
@@ -2503,6 +2509,29 @@ cp_parser_primary_expression (cp_parser *parser,
 	    return build_x_va_arg (expression, type);
 	  }
 
+	case RID_OFFSETOF:
+	  {
+	    tree expression;
+	    bool saved_in_offsetof_p;
+
+	    /* Consume the "__offsetof__" token.  */
+	    cp_lexer_consume_token (parser->lexer);
+	    /* Consume the opening `('.  */
+	    cp_parser_require (parser, CPP_OPEN_PAREN, "`('");
+	    /* Parse the parenthesized (almost) constant-expression.  */
+	    saved_in_offsetof_p = parser->in_offsetof_p;
+	    parser->in_offsetof_p = true;
+	    expression 
+	      = cp_parser_constant_expression (parser,
+					       /*allow_non_constant_p=*/false,
+					       /*non_constant_p=*/NULL);
+	    parser->in_offsetof_p = saved_in_offsetof_p;
+	    /* Consume the closing ')'.  */
+	    cp_parser_require (parser, CPP_CLOSE_PAREN, "`)'");
+
+	    return expression;
+	  }
+
 	default:
 	  cp_parser_error (parser, "expected primary-expression");
 	  return error_mark_node;
@@ -3394,7 +3423,10 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p)
 	   can be used in constant-expressions.  */
 	if (parser->constant_expression_p
 	    && !dependent_type_p (type)
-	    && !INTEGRAL_OR_ENUMERATION_TYPE_P (type))
+	    && !INTEGRAL_OR_ENUMERATION_TYPE_P (type)
+	    /* A cast to pointer or reference type is allowed in the
+	       implementation of "offsetof".  */
+	    && !(parser->in_offsetof_p && POINTER_TYPE_P (type)))
 	  {
 	    if (!parser->allow_non_constant_expression_p)
 	      return (cp_parser_non_constant_expression 
@@ -3854,7 +3886,10 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p)
 	       operator.  */
 	    parser->context->object_type = NULL_TREE;
 	    /* These operators may not appear in constant-expressions.  */
-	    if (parser->constant_expression_p)
+	    if (parser->constant_expression_p
+		/* The "->" operator is allowed in the implementation
+		   of "offsetof".  */
+		&& !(parser->in_offsetof_p && token_type == CPP_DEREF))
 	      {
 		if (!parser->allow_non_constant_expression_p)
 		  postfix_expression 
@@ -4259,7 +4294,10 @@ cp_parser_unary_expression (cp_parser *parser, bool address_p)
 	  break;
 
 	case ADDR_EXPR:
-	  non_constant_p = "`&'";
+	  /* The "&" operator is allowed in the implementation of
+	     "offsetof".  */
+	  if (!parser->in_offsetof_p)
+	    non_constant_p = "`&'";
 	  /* Fall through.  */
 	case BIT_NOT_EXPR:
 	  expression = build_x_unary_op (unary_operator, cast_expression);
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4afe78463a1..21456db1ba6 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -7656,6 +7656,7 @@ Predefined Macros,cpp,The GNU C Preprocessor}).
                         method denoted by a @samp{->*} or @samp{.*} expression.
 * C++ Attributes::      Variable, function, and type attributes for C++ only.
 * Strong Using::      Strong using-directives for namespace composition.
+* Offsetof::            Special syntax for implementing @code{offsetof}.
 * Java Exceptions::     Tweaking exception handling to work with Java.
 * Deprecated Features:: Things will disappear from g++.
 * Backwards Compatibility:: Compatibilities with earlier definitions of C++.
@@ -8295,6 +8296,25 @@ int main()
 @}
 @end smallexample
 
+@node Offsetof
+@section Offsetof
+
+G++ uses a syntactic extension to implement the @code{offsetof} macro.
+
+In particular:
+
+@smallexample
+  __offsetof__ (expression)
+@end smallexample
+
+is equivalent to the parenthesized expression, except that the
+expression is considered an integral constant expression even if it
+contains certain operators that are not normally permitted in an
+integral constant expression.  Users should never use
+@code{__offsetof__} directly; the only valid use of
+@code{__offsetof__} is to implement the @code{offsetof} macro in
+@code{<stddef.h>}.
+
 @node Java Exceptions
 @section Java Exceptions
 
diff --git a/gcc/ginclude/stddef.h b/gcc/ginclude/stddef.h
index d19d78a3140..1bb3e90bc9b 100644
--- a/gcc/ginclude/stddef.h
+++ b/gcc/ginclude/stddef.h
@@ -413,21 +413,12 @@ typedef __WINT_TYPE__ wint_t;
 #ifndef __cplusplus
 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
 #else
-/* In C++ a POD type can have a user defined address-of operator, and
-   that will break offsetof. C++ core defect 273 addresses this and
-   claims that reinterpret_casts to char & type are sufficient to
-   overcome this problem.
-
-   (reinterpret_cast <size_t>
-     (&reinterpret_cast <char &>(static_cast <TYPE *> (0)->MEMBER)))
-
-   But, such casts are not permitted in integral constant expressions,
-   which offsetof is supposed to be.
-
-   It appears that offsetof is unimplementable in C++ without a
-   compiler extension.  */
-#define offsetof(TYPE, MEMBER) (reinterpret_cast <size_t> \
-	(&static_cast<TYPE *> (0)->MEMBER))
+/* The cast to "char &" below avoids problems with user-defined
+   "operator &", which can appear in a POD type.  */
+#define offsetof(TYPE, MEMBER)				\
+  (__offsetof__ (reinterpret_cast <size_t>		\
+                 (&reinterpret_cast <char &>		\
+                  (static_cast<TYPE *> (0)->MEMBER))))
 #endif /* C++ */
 #endif /* _STDDEF_H was defined this time */
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index e31d5d54a61..72832a8c0e6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2003-12-16  Mark Mitchell  <mark@codesourcery.com>
+
+	PR c++/13275
+	* g++.dg/other/offsetof2.C: Remove XFAIL.
+	* g++.dg/parse/offsetof1.C: New test.
+	* g++.gd/parse/offsetof2.C: Likewise.
+
 2003-12-16  Giovanni Bajo  <giovannibajo@gcc.gnu.org>
 
 	* g++.dg/template/nontype3.C: New test.
diff --git a/gcc/testsuite/g++.dg/other/offsetof2.C b/gcc/testsuite/g++.dg/other/offsetof2.C
index 64b4fbdc84d..3ab63981d9b 100644
--- a/gcc/testsuite/g++.dg/other/offsetof2.C
+++ b/gcc/testsuite/g++.dg/other/offsetof2.C
@@ -1,4 +1,4 @@
-// { dg-do run { xfail *-*-* } }
+// { dg-do run }
 // { dg-options -Wold-style-cast }
 
 // Copyright (C) 2003 Free Software Foundation, Inc.
@@ -6,8 +6,6 @@
 
 // DR273 POD can have an operator&, offsetof is still required to work
 
-// XFAILED - you can't write offsetof without an extension
-
 #include <stddef.h>
 
 struct POD1
diff --git a/gcc/testsuite/g++.dg/parse/offsetof1.C b/gcc/testsuite/g++.dg/parse/offsetof1.C
new file mode 100644
index 00000000000..ae9d3110aba
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/offsetof1.C
@@ -0,0 +1,11 @@
+#include <stddef.h>
+
+template <bool> struct StaticAssert;
+template <> struct StaticAssert<true> {};
+
+struct MyPOD
+{
+  int a; int b; int c; 
+};
+
+StaticAssert<(offsetof(MyPOD, a) == 0)> s;
diff --git a/gcc/testsuite/g++.dg/parse/offsetof2.C b/gcc/testsuite/g++.dg/parse/offsetof2.C
new file mode 100644
index 00000000000..4552d39fea2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/offsetof2.C
@@ -0,0 +1,12 @@
+#include <cstddef>
+
+struct choke_me
+{
+    int size;
+    char storage[1];
+};
+
+struct offset_is_broken
+{
+    static const int offset = offsetof(choke_me, storage);
+};