[Powerpc] Tune/optimize powerpc{32,64}/power7/memchr.S.

Assorted tweaking, twisting and tuning to squeeze a few additional cycles
out of the memchr code.   Changes include bypassing the shift pairs
(sld,srd) when they are not required, and unrolling the small_loop that
handles short and trailing strings.

Per scrollpipe data measuring aligned strings for 64-bit, these changes
save between five and eight cycles (9-13% overall) for short strings (<32),
Longer aligned strings see slight improvement of 1-3% due to bypassing the
shifts and the instruction rearranging.

1 files changed, 6 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 0c34ac30cf..12e5b4c2df 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2012-08-21  Will Schmidt  <will_schmidt@vnet.ibm.com>
+
+	* sysdeps/powerpc/powerpc64/power7/memchr.S: Unrolled short loop and
+	slight instruction rearrangements per scrollpipe analysis.
+	* sysdeps/powerpc/powerpc64/power7/memchr.S: Likewise.
+
 2012-08-20  Roland McGrath  <roland@hack.frob.com>
 
 	* manual/syslog.texi (syslog; vsyslog, closelog):