[project @ 2006-01-17 16:13:18 by simonmar]

Improve the GC behaviour of IORefs (see Ticket #650).

This is a small change to the way IORefs interact with the GC, which
should improve GC performance for programs with plenty of IORefs.

Previously we had a single closure type for mutable variables,
MUT_VAR.  Mutable variables were *always* on the mutable list in older
generations, and always traversed on every GC.

Now, we have two closure types: MUT_VAR_CLEAN and MUT_VAR_DIRTY.  The
latter is on the mutable list, but the former is not.  (NB. this
differs from MUT_ARR_PTRS_CLEAN and MUT_ARR_PTRS_DIRTY, both of which
are on the mutable list).  writeMutVar# now implements a write
barrier, by calling dirty_MUT_VAR() in the runtime, that does the
necessary modification of MUT_VAR_CLEAN into MUT_VAR_DIRY, and adding
to the mutable list if necessary.

This results in some pretty dramatic speedups for GHC itself.  I've
just measureed a 30% overall speedup compiling a 31-module program
(anna) with the default heap settings :-D

1 files changed, 2 insertions, 1 deletions

diff --git a/ghc/rts/GCCompact.c b/ghc/rts/GCCompact.c
index 9d05f5d49a..b5bcc19360 100644
--- a/ghc/rts/GCCompact.c
+++ b/ghc/rts/GCCompact.c
@@ -598,7 +598,8 @@ thread_obj (StgInfoTable *info, StgPtr p)
     case CONSTR:
     case STABLE_NAME:
     case IND_PERM:
-    case MUT_VAR:
+    case MUT_VAR_CLEAN:
+    case MUT_VAR_DIRTY:
     case CAF_BLACKHOLE:
     case SE_CAF_BLACKHOLE:
     case SE_BLACKHOLE: