re PR tree-optimization/35609 ("is used uninitialized in this function" should be may warning)

2008-03-19  Richard Guenther  <rguenther@suse.de>

	PR middle-end/35609
	* tree-ssa.c (always_executed): New global flag.
	(warn_uninitialized_var): If !always_executed warn with "maybe"
	instead of "is".
	(execute_early_warn_uninitialized): Compute post-dominators.
	Initialize always_executed before processing each basic block.

	* gcc.dg/testsuite/uninit-15.c: New testcase.
	* gcc.dg/testsuite/uninit-16.c: Likewise.

From-SVN: r133341

1 files changed, 27 insertions, 9 deletions

diff --git a/gcc/tree-ssa.c b/gcc/tree-ssa.c
index a036346dee2..5a67aa8273e 100644
--- a/gcc/tree-ssa.c
+++ b/gcc/tree-ssa.c
@@ -1416,13 +1416,19 @@ warn_uninit (tree t, const char *gmsgid, void *data)
 
   TREE_NO_WARNING (var) = 1;
 }
-   
+
+struct walk_data {
+  tree stmt;
+  bool always_executed;
+};
+
 /* Called via walk_tree, look for SSA_NAMEs that have empty definitions
    and warn about them.  */
 
 static tree
-warn_uninitialized_var (tree *tp, int *walk_subtrees, void *data)
+warn_uninitialized_var (tree *tp, int *walk_subtrees, void *data_)
 {
+  struct walk_data *data = (struct walk_data *)data_;
   tree t = *tp;
 
   switch (TREE_CODE (t))
@@ -1430,7 +1436,12 @@ warn_uninitialized_var (tree *tp, int *walk_subtrees, void *data)
     case SSA_NAME:
       /* We only do data flow with SSA_NAMEs, so that's all we
 	 can warn about.  */
-      warn_uninit (t, "%H%qD is used uninitialized in this function", data);
+      if (data->always_executed)
+        warn_uninit (t, "%H%qD is used uninitialized in this function",
+		     data->stmt);
+      else
+        warn_uninit (t, "%H%qD may be used uninitialized in this function",
+		     data->stmt);
       *walk_subtrees = 0;
       break;
 
@@ -1478,14 +1489,21 @@ execute_early_warn_uninitialized (void)
 {
   block_stmt_iterator bsi;
   basic_block bb;
+  struct walk_data data;
+
+  calculate_dominance_info (CDI_POST_DOMINATORS);
 
   FOR_EACH_BB (bb)
-    for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
-      {
-	tree context = bsi_stmt (bsi);
-	walk_tree (bsi_stmt_ptr (bsi), warn_uninitialized_var,
-		   context, NULL);
-      }
+    {
+      data.always_executed = dominated_by_p (CDI_POST_DOMINATORS,
+					     single_succ (ENTRY_BLOCK_PTR), bb);
+      for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+        {
+	  data.stmt = bsi_stmt (bsi);
+	  walk_tree (bsi_stmt_ptr (bsi), warn_uninitialized_var,
+		     &data, NULL);
+        }
+    }
   return 0;
 }