[PATCH] Restore removal of useless masking in store_field after expand-from-SSA

[Adam Nemet <anemet at caviumnetworks dot com>]

This fixes the last MIPS failure (gcc.target/mips/ins-2.c) after
expand-from-SSA.

When expading a bit-field store we need to look at the defining gimple
statement for the redundant masking conversion.  The reason is that LHS of the
assignment is not a gimple reg so RHS can't include a useful conversion.

Bootstrapping and regtesting on mips64octeon-linux.  OK if it passes?

Adam


	* expr.c (get_def_for_expr): Move it up in the file.
	(store_field): When expanding a bit-field store, look at the
	defining gimple stmt for the masking conversion.

--- expr.c~	2009-05-02 17:31:40.000000000 -0700
+++ expr.c	2009-05-05 00:38:22.000000000 -0700
@@ -2249,6 +2249,26 @@ use_group_regs (rtx *call_fusage, rtx re
 	use_reg (call_fusage, reg);
     }
 }
+
+/* Return the defining gimple statement for SSA_NAME NAME if it is an
+   assigment and the code of the expresion on the RHS is CODE.  Return
+   NULL otherwise.  */
+
+static gimple
+get_def_for_expr (tree name, enum tree_code code)
+{
+  gimple def_stmt;
+
+  if (TREE_CODE (name) != SSA_NAME)
+    return NULL;
+
+  def_stmt = get_gimple_for_ssa_name (name);
+  if (!def_stmt
+      || gimple_assign_rhs_code (def_stmt) != code)
+    return NULL;
+
+  return def_stmt;
+}
 
 
 /* Determine whether the LEN bytes generated by CONSTFUN can be
@@ -5776,22 +5796,25 @@ store_field (rtx target, HOST_WIDE_INT b
 	  && compare_tree_int (TYPE_SIZE (TREE_TYPE (exp)), bitsize) != 0))
     {
       rtx temp;
+      gimple nop_def;
 
       /* If EXP is a NOP_EXPR of precision less than its mode, then that
 	 implies a mask operation.  If the precision is the same size as
 	 the field we're storing into, that mask is redundant.  This is
 	 particularly common with bit field assignments generated by the
 	 C front end.  */
-      if (TREE_CODE (exp) == NOP_EXPR)
+      nop_def = get_def_for_expr (exp, NOP_EXPR);
+      if (nop_def)
 	{
 	  tree type = TREE_TYPE (exp);
 	  if (INTEGRAL_TYPE_P (type)
 	      && TYPE_PRECISION (type) < GET_MODE_BITSIZE (TYPE_MODE (type))
 	      && bitsize == TYPE_PRECISION (type))
 	    {
-	      type = TREE_TYPE (TREE_OPERAND (exp, 0));
+	      tree op = gimple_assign_rhs1 (nop_def);
+	      type = TREE_TYPE (op);
 	      if (INTEGRAL_TYPE_P (type) && TYPE_PRECISION (type) >= bitsize)
-		exp = TREE_OPERAND (exp, 0);
+		exp = op;
 	    }
 	}
 
@@ -6992,26 +7015,6 @@ expand_constructor (tree exp, rtx target
   return target;
 }
 
-/* Return the defining gimple statement for SSA_NAME NAME if it is an
-   assigment and the code of the expresion on the RHS is CODE.  Return
-   NULL otherwise.  */
-
-static gimple
-get_def_for_expr (tree name, enum tree_code code)
-{
-  gimple def_stmt;
-
-  if (TREE_CODE (name) != SSA_NAME)
-    return NULL;
-
-  def_stmt = get_gimple_for_ssa_name (name);
-  if (!def_stmt
-      || gimple_assign_rhs_code (def_stmt) != code)
-    return NULL;
-
-  return def_stmt;
-}
-
 
 /* expand_expr: generate code for computing expression EXP.
    An rtx for the computed value is returned.  The value is never null.