re PR debug/44832 (-fcompare-debug failure for C++ i386.c)

2010-07-10  Richard Guenther  <rguenther@suse.de>
	    Joern Rennecke  <joern.rennecke@embecosm.com>

	PR debug/44832
	* tree-ssa-live.c (mark_all_vars_used_1): Set TREE_USED for
	LABEL_DECL.
	(remove_unused_scope_block_p): Don't drop TREE_USED LABEL_DECLs
	unless they have DECL_IGNORED_P set.

Co-Authored-By: Joern Rennecke <joern.rennecke@embecosm.com>

From-SVN: r162035

gcc/ChangeLog

 2010-07-10  Richard Guenther  <rguenther@suse.de>
+	    Joern Rennecke  <joern.rennecke@embecosm.com>
+
+	PR debug/44832
+	* tree-ssa-live.c (mark_all_vars_used_1): Set TREE_USED for
+	LABEL_DECL.
+	(remove_unused_scope_block_p): Don't drop TREE_USED LABEL_DECLs
+	unless they have DECL_IGNORED_P set.
+
+2010-07-10  Richard Guenther  <rguenther@suse.de>
 
 	PR lto/44889
 	* gimple.c (gimple_fixup_complete_and_incomplete_subtype_p): New

gcc/tree-ssa-live.c

@@ -383,6 +383,14 @@ mark_all_vars_used_1 (tree *tp, int *walk_subtrees, void *data)
 	}
       set_is_used (t);
     }
+  /* remove_unused_scope_block_p requires information about labels
+     which are not DECL_IGNORED_P to tell if they might be used in the IL.  */
+  if (TREE_CODE (t) == LABEL_DECL)
+    /* Although the TREE_USED values that the frontend uses would be
+       acceptable (albeit slightly over-conservative) for our purposes,
+       init_vars_expansion clears TREE_USED for LABEL_DECLs too, so we
+       must re-compute it here.  */
+    TREE_USED (t) = 1;
 
   if (IS_TYPE_OR_DECL_P (t))
     *walk_subtrees = 0;
@@ -462,6 +470,19 @@ remove_unused_scope_block_p (tree scope)
       else if ((ann = var_ann (*t)) != NULL
 		&& ann->used)
 	unused = false;
+      else if (TREE_CODE (*t) == LABEL_DECL && TREE_USED (*t))
+	/* For labels that are still used in the IL, the decision to
+	   preserve them must not depend DEBUG_INFO_LEVEL, otherwise we
+	   risk having different ordering in debug vs.  non-debug builds
+	   during inlining or versioning.
+	   A label appearing here (we have already checked DECL_IGNORED_P)
+	   should not be used in the IL unless it has been explicitly used
+	   before, so we use TREE_USED as an approximation.  */
+	/* In principle, we should do the same here as for the debug case
+	   below, however, when debugging, there might be additional nested
+	   levels that keep an upper level with a label live, so we have to
+	   force this block to be considered used, too.  */
+	unused = false;
 
       /* When we are not doing full debug info, we however can keep around
 	 only the used variables for cfgexpand's memory packing saving quite