[varmap] Emit precise start-of-life

[Michael Matz <matz at suse dot de>]

Hi,

when a decl has only one location dwarf2out.c doesn't generate a location 
list but simply a location description.  A debugger would interpret this 
as that decl having the location in all instructions of the function.  We 
can do better as we at least know at which instruction this is the case.  
We now emit a location list from the single label up to the function end, 
like we already do for the last node when a decl has a multi-node 
location list.


Ciao,
Michael.
-- 
	* dwarf2out.c (add_location_or_const_value_attribute): When a
	decl only has one location nevertheless note it's start of live.

Index: dwarf2out.c
===================================================================
--- dwarf2out.c	(revision 130292)
+++ dwarf2out.c	(working copy)
@@ -10808,7 +10808,29 @@ add_location_or_const_value_attribute (d
       descr = loc_descriptor (NOTE_VAR_LOCATION (node->var_loc_note), status);
       if (descr)
 	{
-	  add_AT_location_description (die, attr, descr);
+	  /* If we have a label the life of DECL starts there, so make
+	     a location list.  */
+	  if (node->label)
+	    {
+	      dw_loc_list_ref list;
+	      const char *endname;
+	      char label_id[MAX_ARTIFICIAL_LABEL_BYTES];
+	      if (!current_function_decl)
+		endname = text_end_label;
+	      else
+		{
+		  ASM_GENERATE_INTERNAL_LABEL (label_id, FUNC_END_LABEL,
+					       current_function_funcdef_no);
+		  endname = ggc_strdup (label_id);
+		}
+	      list = new_loc_list (descr, node->label, endname,
+				   secname_for_decl (decl), 1);
+	      add_AT_loc_list (die, attr, list);
+	    }
+	  else
+	    /* Otherwise at least note the location, as if it was valid
+	       for the whole function.  */
+	    add_AT_location_description (die, attr, descr);
 	  return;
 	}
     }