[project @ 2005-02-28 17:01:13 by simonmar]

Optimisation: the update code only needs to check whether the closure
being updated is a BLACKHOLE_BQ if it has been blackholed; which is
only the case after lazy blackholing has taken place.

So to avoid this unnecessary cost, we have two kinds of update frame:
one which checks for BLACKHOLE_BQ and one that doesn't, and the lazy
blackholing algorithm converts the latter kind into the former as it
replaces thunks with blackholes.

1 files changed, 5 insertions, 0 deletions

diff --git a/ghc/rts/GC.c b/ghc/rts/GC.c
index a470f32c08..75f11a291d 100644
--- a/ghc/rts/GC.c
+++ b/ghc/rts/GC.c
@@ -4121,6 +4121,11 @@ threadSqueezeStack(StgTSO *tso)
 		    // Todo: maybe use SET_HDR() and remove LDV_RECORD_CREATE()?
 		    SET_INFO(bh,&stg_BLACKHOLE_info);
 
+		    // Set the update frame to stg_bh_upd_info, which
+		    // checks for blackholes (the normal update frame
+		    // doesn't check, for efficiency).
+		    ((StgClosure *)frame)->header.info = &stg_bh_upd_frame_info;
+
 		    // We pretend that bh has just been created.
 		    LDV_RECORD_CREATE(bh);
 		}