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[C++] Remove K&R declaration hack.

Message ID 7e358ddd-707a-8e56-b6f1-2b8cefecec7f@acm.org
State New
Headers show
Series [C++] Remove K&R declaration hack. | expand

Commit Message

Nathan Sidwell Aug. 29, 2018, 4:09 p.m. UTC 
When SYSTEM_IMPLICIT_EXTERN_C is in effect, we have a couple of hacks to 
allow unprototyped declarations.
1) in decls_match we look at the promoted return types
2) in decls_match and in the parser we allow '()' to mean '(...)'.

This is of course horrible, #2 will fail badly on modern ABIs. #1 may 
well break sign extension behaviour of smaller-than-int return types.

As it happens the only remaining SIEC target is AIX, and its system 
header files are sufficiently prototyped (including 'int open (const 
char *, int, ...)').

I've bootstrapped this patch on powerpc8-aix with no change in test 
results.  (Thanks David on helping with that.)

IMHO we don't need to warn about this going way first.  If it did affect 
a target it'd be very noisy.

I'll commit in a few days, unless there are objections.

nathan
diff mbox series

Patch

2018-08-29  Nathan Sidwell  <nathan@acm.org>

	gcc/
	* doc/extend.texi (Backwards Compatibility): Remove implicit
	extern C leeway of () being (...).
	gcc/cp/
	* decl.c (decls_match): Remove SYSTEM_IMPLICIT_EXTERN_C matching
	of return types and parms.
	* parser.c (cp_parser_parameter_declaration_clause): Likewise,
	'()' always means '(void)'.

Index: gcc/cp/decl.c
===================================================================
--- gcc/cp/decl.c	(revision 263897)
+++ gcc/cp/decl.c	(working copy)
@@ -968,30 +968,12 @@  decls_match (tree newdecl, tree olddecl,
       if (same_type_p (TREE_TYPE (f1), r2))
 	{
 	  if (!prototype_p (f2) && DECL_EXTERN_C_P (olddecl)
-	      && (fndecl_built_in_p (olddecl)
-#ifdef SYSTEM_IMPLICIT_EXTERN_C
-		  || (DECL_IN_SYSTEM_HEADER (newdecl) && !DECL_CLASS_SCOPE_P (newdecl))
-		  || (DECL_IN_SYSTEM_HEADER (olddecl) && !DECL_CLASS_SCOPE_P (olddecl))
-#endif
-	      ))
+	      && fndecl_built_in_p (olddecl))
 	    {
 	      types_match = self_promoting_args_p (p1);
 	      if (p1 == void_list_node)
 		TREE_TYPE (newdecl) = TREE_TYPE (olddecl);
 	    }
-#ifdef SYSTEM_IMPLICIT_EXTERN_C
-	  else if (!prototype_p (f1)
-		   && (DECL_EXTERN_C_P (olddecl)
-		       && DECL_IN_SYSTEM_HEADER (olddecl)
-		       && !DECL_CLASS_SCOPE_P (olddecl))
-		   && (DECL_EXTERN_C_P (newdecl)
-		       && DECL_IN_SYSTEM_HEADER (newdecl)
-		       && !DECL_CLASS_SCOPE_P (newdecl)))
-	    {
-	      types_match = self_promoting_args_p (p2);
-	      TREE_TYPE (newdecl) = TREE_TYPE (olddecl);
-	    }
-#endif
 	  else
 	    types_match =
 	      compparms (p1, p2)
Index: gcc/cp/parser.c
===================================================================
--- gcc/cp/parser.c	(revision 263897)
+++ gcc/cp/parser.c	(working copy)
@@ -21372,16 +21372,7 @@  cp_parser_parameter_declaration_clause (
     }
   else if (token->type == CPP_CLOSE_PAREN)
     /* There are no parameters.  */
-    {
-#ifdef SYSTEM_IMPLICIT_EXTERN_C
-      if (in_system_header_at (input_location)
-	  && current_class_type == NULL
-	  && current_lang_name == lang_name_c)
-	return NULL_TREE;
-      else
-#endif
-	return void_list_node;
-    }
+    return void_list_node;
   /* Check for `(void)', too, which is a special case.  */
   else if (token->keyword == RID_VOID
 	   && (cp_lexer_peek_nth_token (parser->lexer, 2)->type
Index: gcc/doc/extend.texi
===================================================================
--- gcc/doc/extend.texi	(revision 263897)
+++ gcc/doc/extend.texi	(working copy)
@@ -23685,9 +23685,9 @@  deprecated.   @xref{Deprecated Features}
 @item Implicit C language
 Old C system header files did not contain an @code{extern "C" @{@dots{}@}}
 scope to set the language.  On such systems, all system header files are
-implicitly scoped inside a C language scope.  Also, an empty prototype
-@code{()} is treated as an unspecified number of arguments, rather
-than no arguments, as C++ demands.
+implicitly scoped inside a C language scope.  Such headers must
+correctly prototype function argument types, there is no leeway for
+@code{()} to indicate an unspecified set of arguments.
 
 @end table