[Valgrind-developers] vex: r2236 - trunk/priv

[<sv...@va...>]

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 */