[src/trunk]: src/sys/arch/arm/arm Conditional execution still takes one cycle...

[matt <matt%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c2990931a5e1
branches:  trunk
changeset: 783461:c2990931a5e1
user:      matt <matt%NetBSD.org@localhost>
date:      Sun Dec 23 13:26:21 2012 +0000

description:
Conditional execution still takes one cycle per skipped instruction.
branch to unlikely cases instead of conditionally skipping them.

diffstat:

 sys/arch/arm/arm/cpu_in_cksum_fold.S |  14 +++++++++-----
 1 files changed, 9 insertions(+), 5 deletions(-)

diffs (38 lines):

diff -r d39f7ca279e1 -r c2990931a5e1 sys/arch/arm/arm/cpu_in_cksum_fold.S
--- a/sys/arch/arm/arm/cpu_in_cksum_fold.S      Sun Dec 23 13:24:22 2012 +0000
+++ b/sys/arch/arm/arm/cpu_in_cksum_fold.S      Sun Dec 23 13:26:21 2012 +0000
@@ -1,4 +1,3 @@
-/*     $NetBSD: cpu_in_cksum_fold.S,v 1.3 2012/12/20 07:20:04 matt Exp $       */
 /*-
  * Copyright (c) 2012 The NetBSD Foundation, Inc.
  * All rights reserved.
@@ -49,16 +48,15 @@
         * return a complement of the lower halfword, that's 0xfffe.
         */
        adcs    ip, ip, #0              /* add final carry bit */
-       subeq   r0, r1, #1              /* zero?  complement the carry */
-       RETc(eq)                        /*        and return 0xfffe */
+       beq     1f                      /*   0?  return 0xfffe */
+
        /*
         * Now prevent the adding of 0xffff to 0xffff by making sure the upper
         * halfword isn't 0xffff.  If it is, just complement all 32-bits
         * which clears the upper halfword and complements the lower halfword.
         */
        cmp     ip, r1, lsl #16         /* is the upper halfword 0xffff? */
-       mvneq   r0, ip                  /*   yes, complement */
-       RETc(eq)                        /*        and return */
+       beq     2f                      /*   yes, complement and return */
        /*
         * Finally add the lower halfword to the upper halfword.  If we have
         * a result >= 0x10000, carry will be set.  The maximum result will
@@ -69,3 +67,9 @@
        addcs   ip, ip, #0x10000
        eor     r0, r1, ip, lsr #16
        RET
+
+1:     sub     r0, r1, #1              /* set return value to 0xfffe */
+       RET                             /* return */
+2:     mvn     r0, ip                  /* complement */
+       RET                             /* return */
+