[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, 11 insertions, 2 deletions

diff --git a/ghc/compiler/codeGen/CgPrimOp.hs b/ghc/compiler/codeGen/CgPrimOp.hs
index 7784efbb2b..91aa3911f8 100644
--- a/ghc/compiler/codeGen/CgPrimOp.hs
+++ b/ghc/compiler/codeGen/CgPrimOp.hs
@@ -10,13 +10,15 @@ module CgPrimOp (
    cgPrimOp
  ) where
 
+import ForeignCall	( CCallConv(CCallConv) )
 import StgSyn		( StgLiveVars, StgArg )
 import CgBindery	( getVolatileRegs, getArgAmodes )
 import CgMonad
 import CgInfoTbls	( getConstrTag )
 import CgUtils		( cmmOffsetW, cmmOffsetB, cmmLoadIndexW )
 import Cmm
-import CLabel		( mkMAP_FROZEN_infoLabel, mkMAP_DIRTY_infoLabel )
+import CLabel		( mkMAP_FROZEN_infoLabel, mkMAP_DIRTY_infoLabel,
+			  mkDirty_MUT_VAR_Label )
 import CmmUtils
 import MachOp
 import SMRep
@@ -113,7 +115,14 @@ emitPrimOp [res] ReadMutVarOp [mutv] live
    = stmtC (CmmAssign res (cmmLoadIndexW mutv fixedHdrSize))
 
 emitPrimOp [] WriteMutVarOp [mutv,var] live
-   = stmtC (CmmStore (cmmOffsetW mutv fixedHdrSize) var)
+   = do
+	stmtC (CmmStore (cmmOffsetW mutv fixedHdrSize) var)
+	vols <- getVolatileRegs live
+	stmtC (CmmCall (CmmForeignCall (CmmLit (CmmLabel mkDirty_MUT_VAR_Label))
+				CCallConv) 
+			[{-no results-}]
+			[(mutv,PtrHint)]
+			(Just vols))
 
 --  #define sizzeofByteArrayzh(r,a) \
 --     r = (((StgArrWords *)(a))->words * sizeof(W_))