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Subject: [Bug tree-optimization/37242] missed FRE opportunity because of signedness of addition
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From: "bonzini at gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #10 from bonzini at gnu dot org  2008-08-27 19:53 -------
Yet another piece of the puzzle:
Index: tree-ssa-sccvn.c
===================================================================
--- tree-ssa-sccvn.c    (revision 139423)
+++ tree-ssa-sccvn.c    (working copy)
@@ -2052,6 +2052,40 @@ valueize_expr (tree expr)
   return expr;
 }

+static tree
+make_expression_gimple (tree t)
+{
+  enum gimple_rhs_class grc = get_gimple_rhs_class (TREE_CODE (t));
+  tree op0 = NULL, op1 = NULL;
+
+  switch (grc)
+    {
+    case GIMPLE_UNARY_RHS:
+      op0 = TREE_OPERAND (t, 0);
+      if (!is_gimple_val (op0))
+        op0 = vn_nary_op_lookup (op0, NULL);
+      if (op0)
+        return build1 (TREE_CODE (t), TREE_TYPE (t), op0);
+      break;
+
+    case GIMPLE_BINARY_RHS:
+      op0 = TREE_OPERAND (t, 0);
+      op1 = TREE_OPERAND (t, 1);
+      if (!is_gimple_val (op0))
+        op0 = vn_nary_op_lookup (op0, NULL);
+      if (!is_gimple_val (op1))
+        op1 = vn_nary_op_lookup (op1, NULL);
+      if (op0 && op1)
+        return build2 (TREE_CODE (t), TREE_TYPE (t), op0, op1);
+      break;
+
+    default:
+      break;
+    }
+
+  return NULL;
+}
+
 /* Simplify the binary expression RHS, and return the result if
    simplified. */

@@ -2100,10 +2134,14 @@ simplify_binary_expression (gimple stmt)
      of operators of operators (IE (a + b) + (a + c))
      Otherwise, we will end up with unbounded expressions if
      fold does anything at all.  */
-  if (result && valid_gimple_rhs_p (result))
-    return result;
+  if (result)
+    {
+      STRIP_USELESS_TYPE_CONVERSION (result);
+      if (!valid_gimple_rhs_p (result))
+        result = make_expression_gimple (result);
+    }

-  return NULL_TREE;
+  return result;
 }

 /* Simplify the unary expression RHS, and return the result if
@@ -2153,11 +2191,11 @@ simplify_unary_expression (gimple stmt)
   if (result)
     {
       STRIP_USELESS_TYPE_CONVERSION (result);
-      if (valid_gimple_rhs_p (result))
-        return result;
+      if (!valid_gimple_rhs_p (result))
+        result = make_expression_gimple (result);
     }

-  return NULL_TREE;
+  return result;
 }

 /* Try to simplify RHS using equivalences and constant folding.  */

However it still does not work because the two "unsigned" types do not match.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242