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From: <sv...@va...> - 2012-01-04 01:39:38
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Author: florian
Date: 2012-01-04 01:34:53 +0000 (Wed, 04 Jan 2012)
New Revision: 2236
Log:
Add a comment about setting aside a register for VG_(dispatch_ctr)
on s390.
Modified:
trunk/priv/host_s390_defs.c
Modified: trunk/priv/host_s390_defs.c
===================================================================
--- trunk/priv/host_s390_defs.c 2011-12-18 15:51:54 UTC (rev 2235)
+++ trunk/priv/host_s390_defs.c 2012-01-04 01:34:53 UTC (rev 2236)
@@ -144,7 +144,12 @@
Otherwise, they are available to the allocator */
(*arr)[i++] = mkHReg(10, HRcInt64, False);
(*arr)[i++] = mkHReg(11, HRcInt64, False);
- /* GPR12 is not available because it caches VG_(dispatch_ctr) */
+ /* GPR12 is not available because it caches VG_(dispatch_ctr).
+ Setting aside a register for the counter gives slightly better
+ performance - most of the time. From the 10 tests in "make perf"
+ 8 run faster with a max observed speedup of 2.6% for bz2. ffbench
+ is the counter example. It runs 1.3% faster without the dedicated
+ register. */
/* GPR13 is not available because it is used as guest state pointer */
/* GPR14 is not available because it is used as link register */
/* GPR15 is not available because it is used as stack pointer */
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