This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Recognize another way to express rotation
- To: egcs-patches at egcs dot cygnus dot com
- Subject: Recognize another way to express rotation
- From: Marc Espie <espie at schutzenberger dot liafa dot jussieu dot fr>
- Date: Wed, 13 Oct 1999 17:37:38 +0200
- Reply-To: Marc dot Espie at liafa dot jussieu dot fr
Xor can be used to encore rotations. In fact, it may seem more
natural for a hash function, e.g.,
i = (i << 2) ^ (i >> 30) ^ *n++;
instead of
i = ((i << 2) | (i >> 30)) ^ *n++;
Wed Oct 13 17:27:05 CEST 1999 Marc Espie <espie@cvs.openbsd.org>
* combine.c (simplify_logical): recognize xor pattern that encodes
rotation.
--- combine.c.orig Wed Oct 13 17:24:54 1999
+++ combine.c Wed Oct 13 17:26:27 1999
@@ -5217,6 +5217,21 @@ simplify_logical (x, last)
&& reversible_comparison_p (op0))
return gen_rtx_combine (reverse_condition (GET_CODE (op0)),
mode, XEXP (op0, 0), XEXP (op0, 1));
+
+ /* Convert (xor (ashift A CX) (lshiftrt A CY)) where CX+CY equals the
+ mode size to (rotate A CX). */
+
+ if (((GET_CODE (op0) == ASHIFT && GET_CODE (op1) == LSHIFTRT)
+ || (GET_CODE (op1) == ASHIFT && GET_CODE (op0) == LSHIFTRT))
+ && rtx_equal_p (XEXP (op0, 0), XEXP (op1, 0))
+ && GET_CODE (XEXP (op0, 1)) == CONST_INT
+ && GET_CODE (XEXP (op1, 1)) == CONST_INT
+ && (INTVAL (XEXP (op0, 1)) + INTVAL (XEXP (op1, 1))
+ == GET_MODE_BITSIZE (mode)))
+ return gen_rtx_ROTATE (mode, XEXP (op0, 0),
+ (GET_CODE (op0) == ASHIFT
+ ? XEXP (op0, 1) : XEXP (op1, 1)));
+
break;
default: