combine.c (simplify_comparison): Shift a NOT out of a single bit test.

        * combine.c (simplify_comparison): Shift a NOT out of a single
        bit test.

From-SVN: r36508

gcc/ChangeLog

 2000-09-18  Richard Henderson  <rth@cygnus.com>
 
+	* combine.c (simplify_comparison): Shift a NOT out of a single
+	bit test.
+
 	* combine.c (if_then_else_cond): Canonicalize BImode true to
 	STORE_FLAG_VALUE.
 	* explow.c (trunc_int_for_mode): Likewise.

gcc/combine.c

@@ -10811,6 +10811,21 @@ simplify_comparison (code, pop0, pop1)
 	      continue;
 	    }
 
+	  /* Convert (ne (and (lshiftrt (not X)) 1) 0) to
+	     (eq (and (lshiftrt X) 1) 0).  */
+	  if (const_op == 0 && equality_comparison_p
+	      && XEXP (op0, 1) == const1_rtx
+	      && GET_CODE (XEXP (op0, 0)) == LSHIFTRT
+	      && GET_CODE (XEXP (XEXP (op0, 0), 0)) == NOT)
+	    {
+	      op0 = simplify_and_const_int
+		(op0, mode, gen_rtx_combine (LSHIFTRT, mode,
+					     XEXP (XEXP (XEXP (op0, 0), 0), 0),
+					     XEXP (XEXP (op0, 0), 1)),
+		 (HOST_WIDE_INT) 1);
+	      code = (code == NE ? EQ : NE);
+	      continue;
+	    }
 	  break;
 
 	case ASHIFT: