Tweaks to stack squeezing

1. We weren't squeezing two frames if one of them was a marked update
   frame.  This is easy to fix.

2. The heuristic to decide whether to squeeze was a little
   conservative.  It's worth copying 3 words to save an update frame.

diff --git a/rts/ThreadPaused.c b/rts/ThreadPaused.c
index 5b64f76..3aa66ed 100644 (file)
--- a/rts/ThreadPaused.c
+++ b/rts/ThreadPaused.c
@@ -50,7 +50,7 @@ stackSqueeze(StgTSO *tso, StgPtr bottom)
     current_gap_size = 0;
     gap = (struct stack_gap *) (tso->sp - sizeofW(StgUpdateFrame));
 
-    while (frame < bottom) {
+    while (frame <= bottom) {
        
        info = get_ret_itbl((StgClosure *)frame);
        switch (info->i.type) {
@@ -202,6 +202,11 @@ threadPaused(Capability *cap, StgTSO *tso)
     while (1) {
        // If we've already marked this frame, then stop here.
        if (frame->header.info == (StgInfoTable *)&stg_marked_upd_frame_info) {
+           if (prev_was_update_frame) {
+               words_to_squeeze += sizeofW(StgUpdateFrame);
+               weight += weight_pending;
+               weight_pending = 0;
+           }
            goto end;
        }
 
@@ -305,7 +310,7 @@ end:
     // the number of words we have to shift down is less than the
     // number of stack words we squeeze away by doing so.
     if (RtsFlags.GcFlags.squeezeUpdFrames == rtsTrue &&
-       weight < words_to_squeeze) {
+       ((weight <= 4 && words_to_squeeze > 0) || weight < words_to_squeeze)) {
        stackSqueeze(tso, (StgPtr)frame);
     }
 }