From cf0bdd4b5f3633874ac49b499f3d4914c705dc8c Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Mon, 30 Jul 2001 12:57:01 +0000
Subject: [PATCH] [project @ 2001-07-30 12:57:01 by simonmar] Small perf.
 improvement: use the next bit in the bitmap to indicate
 whether the current object needs to be pushed into the next
 block during compaction.  This saves having to do the
 double traversal of the threaded info pointer list during
 the second pass in most cases.

---
 ghc/rts/GCCompact.c |   25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/ghc/rts/GCCompact.c b/ghc/rts/GCCompact.c
index b3f4fb7..9ddd414 100644
--- a/ghc/rts/GCCompact.c
+++ b/ghc/rts/GCCompact.c
@@ -1,5 +1,5 @@
 /* -----------------------------------------------------------------------------
- * $Id: GCCompact.c,v 1.4 2001/07/25 11:55:57 simonmar Exp $
+ * $Id: GCCompact.c,v 1.5 2001/07/30 12:57:01 simonmar Exp $
  *
  * (c) The GHC Team 2001
  *
@@ -723,8 +723,15 @@ update_fwd_compact( bdescr *blocks )
 
 	    size = p - q;
 	    if (free + size > free_bd->start + BLOCK_SIZE_W) {
+		// unset the next bit in the bitmap to indicate that
+		// this object needs to be pushed into the next
+		// block.  This saves us having to run down the
+		// threaded info pointer list twice during the next pass.
+		unmark(q+1,bd);
 		free_bd = free_bd->link;
 		free = free_bd->start;
+	    } else {
+		ASSERT(is_marked(q+1,bd));
 	    }
 
 	    unthread(q,free);
@@ -784,15 +791,7 @@ update_bkwd_compact( step *stp )
 	    }
 #endif
 
-	    // must unthread before we look at the info ptr...
-	    info = get_threaded_info(p);
-
-	    ASSERT(p && (LOOKS_LIKE_GHC_INFO(info)
-			 || IS_HUGS_CONSTR_INFO(info)));
-
-	    size = obj_sizeW((StgClosure *)p,info);
-
-	    if (free + size > free_bd->start + BLOCK_SIZE_W) {
+	    if (!is_marked(p+1,bd)) {
 		// don't forget to update the free ptr in the block desc.
 		free_bd->free = free;
 		free_bd = free_bd->link;
@@ -801,6 +800,12 @@ update_bkwd_compact( step *stp )
 	    }
 
 	    unthread(p,free);
+	    info = get_itbl((StgClosure *)p);
+	    size = obj_sizeW((StgClosure *)p,info);
+
+	    ASSERT(p && (LOOKS_LIKE_GHC_INFO(info)
+			 || IS_HUGS_CONSTR_INFO(info)));
+
 	    if (free != p) {
 		move(free,p,size);
 	    }
-- 
1.7.10.4