Achieve DECL_INITIAL invariant during C++ function definition

[gkeating at apple dot com (Geoffrey Keating)]

This patch makes DECL_INITIAL consistently have the value
error_mark_node while a function is being defined.  Before it could
also be NULL_TREE or be a BLOCK, neither of which were especially
helpful.

Bootstrapped & tested on powerpc-darwin8.

-- 
- Geoffrey Keating <geoffk@apple.com>

===File ~/patches/gcc-cp-fndeclinitial.patch================
2006-11-30  Geoffrey Keating  <geoffk@apple.com>

	* decl.c (poplevel): Check DECL_INITIAL invariant.
	(duplicate_decls): Preserve DECL_INITIAL when eliminating
	a new definition in favour of an old declaration.
	(start_preparsed_function): Define and document value of
	DECL_INITIAL before and after routine.
	(finish_function): Check DECL_INITIAL invariant.
	* parser.c 
	(cp_parser_function_definition_from_specifiers_and_declarator): 
	Skip duplicate function definitions.

Index: decl.c
===================================================================
--- decl.c	(revision 119380)
+++ decl.c	(working copy)
@@ -756,7 +756,12 @@
 
   leave_scope ();
   if (functionbody)
-    DECL_INITIAL (current_function_decl) = block;
+    {
+      /* The current function is being defined, so its DECL_INITIAL
+	 should be error_mark_node.  */
+      gcc_assert (DECL_INITIAL (current_function_decl) == error_mark_node);
+      DECL_INITIAL (current_function_decl) = block;
+    }
   else if (block)
     current_binding_level->blocks
       = chainon (current_binding_level->blocks, block);
@@ -1632,13 +1637,15 @@
 	}
 
       /* If the new declaration is a definition, update the file and
-	 line information on the declaration.  */
+	 line information on the declaration, and also make
+	 the old declaration the same definition.  */
       if (DECL_INITIAL (old_result) == NULL_TREE
 	  && DECL_INITIAL (new_result) != NULL_TREE)
 	{
 	  DECL_SOURCE_LOCATION (olddecl)
 	    = DECL_SOURCE_LOCATION (old_result)
 	    = DECL_SOURCE_LOCATION (newdecl);
+	  DECL_INITIAL (old_result) = DECL_INITIAL (new_result);
 	  if (DECL_FUNCTION_TEMPLATE_P (newdecl))
 	    DECL_ARGUMENTS (old_result)
 	      = DECL_ARGUMENTS (new_result);
@@ -10363,8 +10370,14 @@
    For C++, we must first check whether that datum makes any sense.
    For example, "class A local_a(1,2);" means that variable local_a
    is an aggregate of type A, which should have a constructor
-   applied to it with the argument list [1, 2].  */
+   applied to it with the argument list [1, 2].
 
+   On entry, DECL_INITIAL (decl1) should be NULL_TREE or error_mark_node,
+   or may be a BLOCK if the function has been defined previously
+   in this translation unit.  On exit, DECL_INITIAL (decl1) will be
+   error_mark_node if the function has never been defined, or
+   a BLOCK if the function has been defined somewhere.  */
+
 void
 start_preparsed_function (tree decl1, tree attrs, int flags)
 {
@@ -10492,24 +10505,6 @@
       cp_apply_type_quals_to_decl (cp_type_quals (restype), resdecl);
     }
 
-  /* Initialize RTL machinery.  We cannot do this until
-     CURRENT_FUNCTION_DECL and DECL_RESULT are set up.  We do this
-     even when processing a template; this is how we get
-     CFUN set up, and our per-function variables initialized.
-     FIXME factor out the non-RTL stuff.  */
-  bl = current_binding_level;
-  allocate_struct_function (decl1);
-  current_binding_level = bl;
-
-  /* Even though we're inside a function body, we still don't want to
-     call expand_expr to calculate the size of a variable-sized array.
-     We haven't necessarily assigned RTL to all variables yet, so it's
-     not safe to try to expand expressions involving them.  */
-  cfun->x_dont_save_pending_sizes_p = 1;
-
-  /* Start the statement-tree, start the tree now.  */
-  DECL_SAVED_TREE (decl1) = push_stmt_list ();
-
   /* Let the user know we're compiling this function.  */
   announce_function (decl1);
 
@@ -10555,10 +10550,34 @@
 	maybe_apply_pragma_weak (decl1);
     }
 
-  /* Reset these in case the call to pushdecl changed them.  */
+  /* Reset this in case the call to pushdecl changed it.  */
   current_function_decl = decl1;
-  cfun->decl = decl1;
 
+  gcc_assert (DECL_INITIAL (decl1));
+
+  /* This function may already have been parsed, in which case just
+     return; our caller will skip over the body without parsing.  */
+  if (DECL_INITIAL (decl1) != error_mark_node)
+    return;
+
+  /* Initialize RTL machinery.  We cannot do this until
+     CURRENT_FUNCTION_DECL and DECL_RESULT are set up.  We do this
+     even when processing a template; this is how we get
+     CFUN set up, and our per-function variables initialized.
+     FIXME factor out the non-RTL stuff.  */
+  bl = current_binding_level;
+  allocate_struct_function (decl1);
+  current_binding_level = bl;
+
+  /* Even though we're inside a function body, we still don't want to
+     call expand_expr to calculate the size of a variable-sized array.
+     We haven't necessarily assigned RTL to all variables yet, so it's
+     not safe to try to expand expressions involving them.  */
+  cfun->x_dont_save_pending_sizes_p = 1;
+
+  /* Start the statement-tree, start the tree now.  */
+  DECL_SAVED_TREE (decl1) = push_stmt_list ();
+
   /* If we are (erroneously) defining a function that we have already
      defined before, wipe out what we knew before.  */
   if (!DECL_PENDING_INLINE_P (decl1))
@@ -11066,6 +11085,10 @@
       which then got a warning when stored in a ptr-to-function variable.  */
 
   gcc_assert (building_stmt_tree ());
+  /* The current function is being defined, so its DECL_INITIAL should
+     be set, and unless there's a multiple definition, it should be
+     error_mark_node.  */
+  gcc_assert (DECL_INITIAL (fndecl) == error_mark_node);
 
   /* For a cloned function, we've already got all the code we need;
      there's no need to add any extra bits.  */
Index: method.c
===================================================================
--- method.c	(revision 119380)
+++ method.c	(working copy)
@@ -407,10 +407,6 @@
 	}
     }
 
-  /* The back-end expects DECL_INITIAL to contain a BLOCK, so we
-     create one.  */
-  DECL_INITIAL (thunk_fndecl) = make_node (BLOCK);
-
   /* Set up cloned argument trees for the thunk.  */
   t = NULL_TREE;
   for (a = DECL_ARGUMENTS (function); a; a = TREE_CHAIN (a))
@@ -424,17 +420,23 @@
     }
   a = nreverse (t);
   DECL_ARGUMENTS (thunk_fndecl) = a;
-  BLOCK_VARS (DECL_INITIAL (thunk_fndecl)) = a;
 
   if (this_adjusting
       && targetm.asm_out.can_output_mi_thunk (thunk_fndecl, fixed_offset,
 					      virtual_value, alias))
     {
       const char *fnname;
+      tree fn_block;
+      
       current_function_decl = thunk_fndecl;
       DECL_RESULT (thunk_fndecl)
 	= build_decl (RESULT_DECL, 0, integer_type_node);
       fnname = XSTR (XEXP (DECL_RTL (thunk_fndecl), 0), 0);
+      /* The back-end expects DECL_INITIAL to contain a BLOCK, so we
+	 create one.  */
+      fn_block = make_node (BLOCK);
+      BLOCK_VARS (fn_block) = a;
+      DECL_INITIAL (thunk_fndecl) = fn_block;
       init_function_start (thunk_fndecl);
       current_function_is_thunk = 1;
       assemble_start_function (thunk_fndecl, fnname);
Index: parser.c
===================================================================
--- parser.c	(revision 119380)
+++ parser.c	(working copy)
@@ -15583,6 +15583,16 @@
       cp_parser_skip_to_end_of_block_or_statement (parser);
       fn = error_mark_node;
     }
+  else if (DECL_INITIAL (current_function_decl) != error_mark_node)
+    {
+      /* Seen already, skip it.  An error message has already been output.  */
+      cp_parser_skip_to_end_of_block_or_statement (parser);
+      fn = current_function_decl;
+      current_function_decl = NULL_TREE;
+      /* If this is a function from a class, pop the nested class.  */
+      if (current_class_name)
+	pop_nested_class ();
+    }
   else
     fn = cp_parser_function_definition_after_declarator (parser,
 							 /*inline_p=*/false);
============================================================