New implementation of BLACKHOLEs

[ghc-hetmet.git] / compiler / codeGen / CgStackery.lhs

diff --git a/compiler/codeGen/CgStackery.lhs b/compiler/codeGen/CgStackery.lhs
index 6683de4..532127a 100644 (file)
--- a/compiler/codeGen/CgStackery.lhs
+++ b/compiler/codeGen/CgStackery.lhs
@@ -17,7 +17,7 @@ module CgStackery (
        setStackFrame, getStackFrame,
        mkVirtStkOffsets, mkStkAmodes,
        freeStackSlots, 
-       pushUpdateFrame, emitPushUpdateFrame,
+       pushUpdateFrame, pushBHUpdateFrame, emitPushUpdateFrame,
     ) where
 
 #include "HsVersions.h"
@@ -265,6 +265,14 @@ to reflect the frame pushed.
 \begin{code}
 pushUpdateFrame :: CmmExpr -> Code -> Code
 pushUpdateFrame updatee code
+  = pushSpecUpdateFrame mkUpdInfoLabel updatee code
+
+pushBHUpdateFrame :: CmmExpr -> Code -> Code
+pushBHUpdateFrame updatee code
+  = pushSpecUpdateFrame mkBHUpdInfoLabel updatee code
+
+pushSpecUpdateFrame :: CLabel -> CmmExpr -> Code -> Code
+pushSpecUpdateFrame lbl updatee code
   = do {
       when debugIsOn $ do
        { EndOfBlockInfo _ sequel <- getEndOfBlockInfo ;
@@ -277,15 +285,25 @@ pushUpdateFrame updatee code
                -- The location of the lowest-address
                -- word of the update frame itself
 
-       ; setEndOfBlockInfo (EndOfBlockInfo vsp UpdateCode) $
-           do  { emitPushUpdateFrame frame_addr updatee
+                -- NB. we used to set the Sequel to 'UpdateCode' so
+                -- that we could jump directly to the update code if
+                -- we know that the next frame on the stack is an
+                -- update frame.  However, the RTS can sometimes
+                -- change an update frame into something else (see
+                -- e.g. Note [upd-black-hole] in rts/sm/Scav.c), so we
+                -- no longer make this assumption.
+       ; setEndOfBlockInfo (EndOfBlockInfo vsp OnStack) $
+           do  { emitSpecPushUpdateFrame lbl frame_addr updatee
                ; code }
        }
 
 emitPushUpdateFrame :: CmmExpr -> CmmExpr -> Code
-emitPushUpdateFrame frame_addr updatee = do
+emitPushUpdateFrame = emitSpecPushUpdateFrame mkUpdInfoLabel
+
+emitSpecPushUpdateFrame :: CLabel -> CmmExpr -> CmmExpr -> Code
+emitSpecPushUpdateFrame lbl frame_addr updatee = do
        stmtsC [  -- Set the info word
-                 CmmStore frame_addr (mkLblExpr mkUpdInfoLabel)
+                 CmmStore frame_addr (mkLblExpr lbl)
                , -- And the updatee
                  CmmStore (cmmOffsetB frame_addr off_updatee) updatee ]
        initUpdFrameProf frame_addr