Re-working of the breakpoint support

This is the result of Bernie Pope's internship work at MSR Cambridge,
with some subsequent improvements by me.  The main plan was to

 (a) Reduce the overhead for breakpoints, so we could enable 
     the feature by default without incurrent a significant penalty
 (b) Scatter more breakpoint sites throughout the code

Currently we can set a breakpoint on almost any subexpression, and the
overhead is around 1.5x slower than normal GHCi.  I hope to be able to
get this down further and/or allow breakpoints to be turned off.

This patch also fixes up :print following the recent changes to
constructor info tables.  (most of the :print tests now pass)

We now support single-stepping, which just enables all breakpoints.

  :step <expr>     executes <expr> with single-stepping turned on
  :step            single-steps from the current breakpoint

The mechanism is quite different to the previous implementation.  We
share code with the HPC (haskell program coverage) implementation now.
The coverage pass annotates source code with "tick" locations which
are tracked by the coverage tool.  In GHCi, each "tick" becomes a
potential breakpoint location.

Previously breakpoints were compiled into code that magically invoked
a nested instance of GHCi.  Now, a breakpoint causes the current
thread to block and control is returned to GHCi.

See the wiki page for more details and the current ToDo list:

  http://hackage.haskell.org/trac/ghc/wiki/NewGhciDebugger

1 files changed, 13 insertions, 6 deletions

diff --git a/compiler/ghci/ByteCodeLink.lhs b/compiler/ghci/ByteCodeLink.lhs
index 9988325dd3..7304d0290b 100644
--- a/compiler/ghci/ByteCodeLink.lhs
+++ b/compiler/ghci/ByteCodeLink.lhs
@@ -27,7 +27,6 @@ import Module
 import PackageConfig
 import FastString
 import Panic
-import Breakpoints
 
 #ifdef DEBUG
 import Outputable
@@ -47,7 +46,7 @@ import GHC.Exts
 import GHC.Arr		( Array(..) )
 import GHC.IOBase	( IO(..) )
 import GHC.Ptr		( Ptr(..), castPtr )
-import GHC.Base		( writeArray#, RealWorld, Int(..) )
+import GHC.Base		( writeArray#, RealWorld, Int(..), Word# )  
 \end{code}
 
 
@@ -143,6 +142,10 @@ mkPtrsArray ie ce n_ptrs ptrs = do
     fill (BCOPtrBCO ul_bco) i = do
 	BCO bco# <- linkBCO' ie ce ul_bco
 	writeArrayBCO marr i bco#
+    fill (BCOPtrBreakInfo brkInfo) i =                    
+        unsafeWrite marr i (unsafeCoerce# brkInfo)
+    fill (BCOPtrArray brkArray) i =                    
+        unsafeWrite marr i (unsafeCoerce# brkArray)
   zipWithM fill ptrs [0..]
   unsafeFreeze marr
 
@@ -163,10 +166,16 @@ writeArrayBCO (IOArray (STArray _ _ marr#)) (I# i#) bco# = IO $ \s# ->
   case (unsafeCoerce# writeArray#) marr# i# bco# s# of { s# ->
   (# s#, () #) }
 
+{-
+writeArrayMBA :: IOArray Int a -> Int -> MutableByteArray# a -> IO ()
+writeArrayMBA (IOArray (STArray _ _ marr#)) (I# i#) mba# = IO $ \s# ->
+  case (unsafeCoerce# writeArray#) marr# i# bco# s# of { s# ->
+  (# s#, () #) }
+-}
+
 data BCO = BCO BCO#
 
-newBCO :: ByteArray# -> ByteArray# -> Array# a
-	 -> Int# -> ByteArray# -> IO BCO
+newBCO :: ByteArray# -> ByteArray# -> Array# a -> Int# -> ByteArray# -> IO BCO
 newBCO instrs lits ptrs arity bitmap
    = IO $ \s -> case newBCO# instrs lits ptrs arity bitmap s of 
 		  (# s1, bco #) -> (# s1, BCO bco #)
@@ -201,8 +210,6 @@ lookupName :: ClosureEnv -> Name -> IO HValue
 lookupName ce nm
    = case lookupNameEnv ce nm of
         Just (_,aa) -> return aa
-        Nothing | Just bk <- lookupBogusBreakpointVal nm
-           -> return bk
         Nothing 
            -> ASSERT2(isExternalName nm, ppr nm)
 	      do let sym_to_find = nameToCLabel nm "closure"