re PR debug/49382 (-O2 -g: DW_AT_location at the very first PC is already modified)

	PR debug/49382
	* dwarf2out.c (dw_loc_list_node): Add force field.
	(add_var_loc_to_decl): For PARM_DECL, attempt to keep
	the incoming location in the list, even if it is modified
	before first real insn.
	(output_loc_list): Emit empty ranges with force flag set.
	(dw_loc_list): If first range of a PARM_DECL is empty,
	set force flag.

From-SVN: r175076

gcc/ChangeLog

+2011-06-15  Jakub Jelinek  <jakub@redhat.com>
+
+	PR debug/49382
+	* dwarf2out.c (dw_loc_list_node): Add force field.
+	(add_var_loc_to_decl): For PARM_DECL, attempt to keep
+	the incoming location in the list, even if it is modified
+	before first real insn.
+	(output_loc_list): Emit empty ranges with force flag set.
+	(dw_loc_list): If first range of a PARM_DECL is empty,
+	set force flag.
+
 2011-06-15  Alexander Monakov  <amonakov@ispras.ru>
 
 	PR target/49349

gcc/dwarf2out.c

@@ -4467,6 +4467,9 @@ typedef struct GTY(()) dw_loc_list_struct {
   /* True if this list has been replaced by dw_loc_next.  */
   bool replaced;
   bool emitted;
+  /* True if the range should be emitted even if begin and end
+     are the same.  */
+  bool force;
 } dw_loc_list_node;
 
 static dw_loc_descr_ref int_loc_descriptor (HOST_WIDE_INT);
@@ -8621,7 +8624,30 @@ add_var_loc_to_decl (tree decl, rtx loc_note, const char *label)
   else
     temp = (var_loc_list *) *slot;
 
-  if (temp->last)
+  /* For PARM_DECLs try to keep around the original incoming value,
+     even if that means we'll emit a zero-range .debug_loc entry.  */
+  if (temp->last
+      && temp->first == temp->last
+      && TREE_CODE (decl) == PARM_DECL
+      && GET_CODE (temp->first->loc) == NOTE
+      && NOTE_VAR_LOCATION_DECL (temp->first->loc) == decl
+      && DECL_INCOMING_RTL (decl)
+      && NOTE_VAR_LOCATION_LOC (temp->first->loc)
+      && GET_CODE (NOTE_VAR_LOCATION_LOC (temp->first->loc))
+	 == GET_CODE (DECL_INCOMING_RTL (decl))
+      && prev_real_insn (temp->first->loc) == NULL_RTX
+      && (bitsize != -1
+	  || !rtx_equal_p (NOTE_VAR_LOCATION_LOC (temp->first->loc),
+			   NOTE_VAR_LOCATION_LOC (loc_note))
+	  || (NOTE_VAR_LOCATION_STATUS (temp->first->loc)
+	      != NOTE_VAR_LOCATION_STATUS (loc_note))))
+    {
+      loc = ggc_alloc_cleared_var_loc_node ();
+      temp->first->next = loc;
+      temp->last = loc;
+      loc->loc = construct_piece_list (loc_note, bitpos, bitsize);
+    }
+  else if (temp->last)
     {
       struct var_loc_node *last = temp->last, *unused = NULL;
       rtx *piece_loc = NULL, last_loc_note;
@@ -8667,7 +8693,9 @@ add_var_loc_to_decl (tree decl, rtx loc_note, const char *label)
 	    }
 	  else
 	    {
-	      gcc_assert (temp->first == temp->last);
+	      gcc_assert (temp->first == temp->last
+			  || (temp->first->next == temp->last
+			      && TREE_CODE (decl) == PARM_DECL));
 	      memset (temp->last, '\0', sizeof (*temp->last));
 	      temp->last->loc = construct_piece_list (loc_note, bitpos, bitsize);
 	      return temp->last;
@@ -11394,7 +11422,7 @@ output_loc_list (dw_loc_list_ref list_head)
     {
       unsigned long size;
       /* Don't output an entry that starts and ends at the same address.  */
-      if (strcmp (curr->begin, curr->end) == 0)
+      if (strcmp (curr->begin, curr->end) == 0 && !curr->force)
 	continue;
       if (!have_multiple_function_sections)
 	{
@@ -16090,6 +16118,11 @@ dw_loc_list (var_loc_list *loc_list, tree decl, int want_address)
 	      }
 
 	    *listp = new_loc_list (descr, node->label, endname, secname);
+	    if (TREE_CODE (decl) == PARM_DECL
+		&& node == loc_list->first
+		&& GET_CODE (node->loc) == NOTE
+		&& strcmp (node->label, endname) == 0)
+	      (*listp)->force = true;
 	    listp = &(*listp)->dw_loc_next;
 
 	    if (range_across_switch)