re PR debug/77692 (gcc.dg/debug/dwarf2/const-2b.c FAILs)

2016-09-26  Richard Biener  <rguenther@suse.de>

	PR debug/77692
	* cgraphunit.c (analyze_functions): Before early removing
	global vars calls the late_global_decl debug handler mark
	the variable as readonly.

From-SVN: r240483

gcc/ChangeLog

+2016-09-26  Richard Biener  <rguenther@suse.de>
+
+	PR debug/77692
+	* cgraphunit.c (analyze_functions): Before early removing
+	global vars calls the late_global_decl debug handler mark
+	the variable as readonly.
+
 2016-09-25  Oleg Endo  <olegendo@gcc.gnu.org>
 
 	PR target/51244

gcc/cgraphunit.c

@@ -1194,8 +1194,15 @@ analyze_functions (bool first_time)
 	     at looking at optimized away DECLs, since
 	     late_global_decl will subsequently be called from the
 	     contents of the now pruned symbol table.  */
-	  if (!decl_function_context (node->decl))
-	    (*debug_hooks->late_global_decl) (node->decl);
+	  if (TREE_CODE (node->decl) == VAR_DECL
+	      && !decl_function_context (node->decl))
+	    {
+	      /* We are reclaiming totally unreachable code and variables
+	         so they effectively appear as readonly.  Show that to
+		 the debug machinery.  */
+	      TREE_READONLY (node->decl) = 1;
+	      (*debug_hooks->late_global_decl) (node->decl);
+	    }
 
 	  node->remove ();
 	  continue;