2008-04-30 Richard Guenther <rguenther@suse.de>

	PR tree-optimization/14847
	* tree-ssa-ifcombine.c (get_name_for_bit_test): New helper function.
	(recognize_bits_test): Use it.
	(recognize_single_bit_test): Likewise.

	* gcc.dg/tree-ssa/ssa-ifcombine-6.c: New testcase.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@134825 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 28 insertions, 2 deletions

diff --git a/gcc/tree-ssa-ifcombine.c b/gcc/tree-ssa-ifcombine.c
index cec5868c636..3a28fadd792 100644
--- a/gcc/tree-ssa-ifcombine.c
+++ b/gcc/tree-ssa-ifcombine.c
@@ -135,6 +135,32 @@ same_phi_args_p (basic_block bb1, basic_block bb2, basic_block dest)
   return true;
 }
 
+/* Return the best representative SSA name for CANDIDATE which is used
+   in a bit test.  */
+
+static tree
+get_name_for_bit_test (tree candidate)
+{
+  /* Skip single-use names in favor of using the name from a
+     non-widening conversion definition.  */
+  if (TREE_CODE (candidate) == SSA_NAME
+      && has_single_use (candidate))
+    {
+      tree def_stmt = SSA_NAME_DEF_STMT (candidate);
+      if (TREE_CODE (def_stmt) == GIMPLE_MODIFY_STMT
+	  && (TREE_CODE (GIMPLE_STMT_OPERAND (def_stmt, 1)) == NOP_EXPR
+	      || TREE_CODE (GIMPLE_STMT_OPERAND (def_stmt, 1)) == CONVERT_EXPR))
+	{
+	  tree rhs = GIMPLE_STMT_OPERAND (def_stmt, 1);
+	  if (TYPE_PRECISION (TREE_TYPE (rhs))
+	      <= TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (rhs, 0))))
+	    return TREE_OPERAND (rhs, 0);
+	}
+    }
+
+  return candidate;
+}
+
 /* Recognize a single bit test pattern in COND_EXPR and its defining
    statements.  Store the name being tested in *NAME and the bit
    in *BIT.  The COND_EXPR computes *NAME & (1 << *BIT).
@@ -192,7 +218,7 @@ recognize_single_bit_test (tree cond_expr, tree *name, tree *bit)
 	{
 	  /* t & 1 */
 	  *bit = integer_zero_node;
-	  *name = orig_name;
+	  *name = get_name_for_bit_test (orig_name);
 	}
 
       return true;
@@ -272,7 +298,7 @@ recognize_bits_test (tree cond_expr, tree *name, tree *bits)
   if (TREE_CODE (t) != BIT_AND_EXPR)
     return false;
 
-  *name = TREE_OPERAND (t, 0);
+  *name = get_name_for_bit_test (TREE_OPERAND (t, 0));
   *bits = TREE_OPERAND (t, 1);
 
   return true;