Nuke dead code

  * CmmRewriteAddignments module was replaced by CmmSink a long
    time ago. That module is now available at
    https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Hoopl/Examples
    wiki page.

  * removeDeadAssignments function was not used and it was also
    moved to the above page.

  * I also nuked some commented out debugging code that was not
    used for 1,5 year.

4 files changed, 5 insertions, 681 deletions

diff --git a/compiler/cmm/CmmLayoutStack.hs b/compiler/cmm/CmmLayoutStack.hs
index 95483a2f52..bdc947829d 100644
--- a/compiler/cmm/CmmLayoutStack.hs
+++ b/compiler/cmm/CmmLayoutStack.hs
@@ -189,16 +189,10 @@ cmmLayoutStack :: DynFlags -> ProcPointSet -> ByteOff -> CmmGraph
 cmmLayoutStack dflags procpoints entry_args
                graph0@(CmmGraph { g_entry = entry })
   = do
-    -- pprTrace "cmmLayoutStack" (ppr entry_args) $ return ()
-
-    -- We need liveness info.  We could do removeDeadAssignments at
-    -- the same time, but it buys nothing over doing cmmSink later,
-    -- and costs a lot more than just cmmLocalLiveness.
-    -- (graph, liveness) <- removeDeadAssignments graph0
+    -- We need liveness info. Dead assignments are removed later
+    -- by the sinking pass.
     let (graph, liveness) = (graph0, cmmLocalLiveness dflags graph0)
-
-    -- pprTrace "liveness" (ppr liveness) $ return ()
-    let blocks = postorderDfs graph
+        blocks = postorderDfs graph
 
     (final_stackmaps, _final_high_sp, new_blocks) <-
           mfix $ \ ~(rec_stackmaps, rec_high_sp, _new_blocks) ->
@@ -206,12 +200,9 @@ cmmLayoutStack dflags procpoints entry_args
                    rec_stackmaps rec_high_sp blocks
 
     new_blocks' <- mapM (lowerSafeForeignCall dflags) new_blocks
-
-    -- pprTrace ("Sp HWM") (ppr _final_high_sp) $ return ()
     return (ofBlockList entry new_blocks', final_stackmaps)
 
 
-
 layout :: DynFlags
        -> BlockSet                      -- proc points
        -> BlockEnv CmmLocalLive         -- liveness
@@ -252,8 +243,6 @@ layout dflags procpoints liveness entry entry_args final_stackmaps final_sp_high
                      (pprPanic "no stack map for" (ppr entry_lbl))
                      entry_lbl acc_stackmaps
 
-       -- pprTrace "layout" (ppr entry_lbl <+> ppr stack0) $ return ()
-
        -- (a) Update the stack map to include the effects of
        --     assignments in this block
        let stack1 = foldBlockNodesF (procMiddle acc_stackmaps) middle0 stack0
@@ -273,8 +262,6 @@ layout dflags procpoints liveness entry entry_args final_stackmaps final_sp_high
            <- handleLastNode dflags procpoints liveness cont_info
                              acc_stackmaps stack1 middle0 last0
 
-       -- pprTrace "layout(out)" (ppr out) $ return ()
-
        -- (d) Manifest Sp: run over the nodes in the block and replace
        --     CmmStackSlot with CmmLoad from Sp with a concrete offset.
        --
@@ -514,11 +501,8 @@ handleLastNode dflags procpoints liveness cont_info stackmaps
         = do
              let cont_args = mapFindWithDefault 0 l cont_info
                  (stack2, assigs) =
-                      --pprTrace "first visit to proc point"
-                      --             (ppr l <+> ppr stack1) $
                       setupStackFrame dflags l liveness (sm_ret_off stack0)
-                                                       cont_args stack0
-             --
+                                                        cont_args stack0
              (tmp_lbl, block) <- makeFixupBlock dflags sp0 l stack2 assigs
              return (l, tmp_lbl, stack2, block)
 
@@ -682,8 +666,6 @@ allocate :: DynFlags -> ByteOff -> LocalRegSet -> StackMap
 allocate dflags ret_off live stackmap@StackMap{ sm_sp = sp0
                                               , sm_regs = regs0 }
  =
-  -- pprTrace "allocate" (ppr live $$ ppr stackmap) $
-
    -- we only have to save regs that are not already in a slot
    let to_save = filter (not . (`elemUFM` regs0)) (Set.elems live)
        regs1   = filterUFM (\(r,_) -> elemRegSet r live) regs0
@@ -923,8 +905,7 @@ elimStackStores stackmap stackmaps area_off nodes
          CmmStore (CmmStackSlot area m) (CmmReg (CmmLocal r))
             | Just (_,off) <- lookupUFM (sm_regs stackmap) r
             , area_off area + m == off
-            -> -- pprTrace "eliminated a node!" (ppr r) $
-               go stackmap ns
+            -> go stackmap ns
          _otherwise
             -> n : go (procMiddle stackmaps n stackmap) ns
 
diff --git a/compiler/cmm/CmmLive.hs b/compiler/cmm/CmmLive.hs
index 7d674b76a2..e66ab73f8a 100644
--- a/compiler/cmm/CmmLive.hs
+++ b/compiler/cmm/CmmLive.hs
@@ -11,7 +11,6 @@ module CmmLive
     , cmmGlobalLiveness
     , liveLattice
     , noLiveOnEntry, xferLive, gen, kill, gen_kill
-    , removeDeadAssignments
     )
 where
 
@@ -98,30 +97,3 @@ xferLive dflags = mkBTransfer3 fst mid lst
         mid n f = gen_kill dflags n f
         lst :: CmmNode O C -> FactBase (CmmLive r) -> CmmLive r
         lst n f = gen_kill dflags n $ joinOutFacts liveLattice n f
-
------------------------------------------------------------------------------
--- Removing assignments to dead variables
------------------------------------------------------------------------------
-
-removeDeadAssignments :: DynFlags -> CmmGraph
-                      -> UniqSM (CmmGraph, BlockEnv CmmLocalLive)
-removeDeadAssignments dflags g =
-   dataflowPassBwd g [] $ analRewBwd liveLattice (xferLive dflags) rewrites
-   where rewrites = mkBRewrite3 nothing middle nothing
-         -- SDM: no need for deepBwdRw here, we only rewrite to empty
-         -- Beware: deepBwdRw with one polymorphic function seems more
-         -- reasonable here, but GHC panics while compiling, see bug
-         -- #4045.
-         middle :: CmmNode O O -> Fact O CmmLocalLive -> CmmReplGraph O O
-         middle (CmmAssign (CmmLocal reg') _) live
-                 | not (reg' `elemRegSet` live)
-                 = return $ Just emptyGraph
-         -- XXX maybe this should be somewhere else...
-         middle (CmmAssign lhs (CmmReg rhs))   _ | lhs == rhs
-                 = return $ Just emptyGraph
-         middle (CmmStore lhs (CmmLoad rhs _)) _ | lhs == rhs
-                 = return $ Just emptyGraph
-         middle _ _ = return Nothing
-
-         nothing :: CmmNode e x -> Fact x CmmLocalLive -> CmmReplGraph e x
-         nothing _ _ = return Nothing
diff --git a/compiler/cmm/CmmRewriteAssignments.hs b/compiler/cmm/CmmRewriteAssignments.hs
deleted file mode 100644
index 3c0a05b949..0000000000
--- a/compiler/cmm/CmmRewriteAssignments.hs
+++ /dev/null
@@ -1,628 +0,0 @@
-{-# LANGUAGE ViewPatterns #-}
-{-# LANGUAGE GADTs #-}
-{-# LANGUAGE FlexibleContexts #-}
-
-{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
-
--- This module implements generalized code motion for assignments to
--- local registers, inlining and sinking when possible.  It also does
--- some amount of rewriting for stores to register slots, which are
--- effectively equivalent to local registers.
-module CmmRewriteAssignments
-  ( rewriteAssignments
-  ) where
-
-import StgCmmUtils -- XXX layering violation
-
-import Cmm
-import CmmUtils
-import CmmOpt
-
-import DynFlags
-import UniqSupply
-import UniqFM
-import Unique
-import BlockId
-
-import Hoopl
-import Compiler.Hoopl ((<*>), mkMiddle, mkLast)
-import Data.Maybe
-import Control.Monad
-import Prelude hiding (succ, zip)
-
-----------------------------------------------------------------
---- Main function
-
-rewriteAssignments :: DynFlags -> CmmGraph -> UniqSM CmmGraph
-rewriteAssignments dflags g = do
-  -- Because we need to act on forwards and backwards information, we
-  -- first perform usage analysis and bake this information into the
-  -- graph (backwards transform), and then do a forwards transform
-  -- to actually perform inlining and sinking.
-  g'  <- annotateUsage dflags g
-  g'' <- liftM fst $ dataflowPassFwd g' [(g_entry g, fact_bot assignmentLattice)] $
-                                     analRewFwd assignmentLattice
-                                                (assignmentTransfer dflags)
-                                                (assignmentRewrite dflags `thenFwdRw` machOpFoldRewrite dflags)
-  return (modifyGraph eraseRegUsage g'')
-
-----------------------------------------------------------------
---- Usage information
-
--- We decorate all register assignments with approximate usage
--- information, that is, the maximum number of times the register is
--- referenced while it is live along all outgoing control paths.
--- This analysis provides a precise upper bound for usage, so if a
--- register is never referenced, we can remove it, as that assignment is
--- dead.
---
--- This analysis is very similar to liveness analysis; we just keep a
--- little extra info. (Maybe we should move it to CmmLive, and subsume
--- the old liveness analysis.)
---
--- There are a few subtleties here:
---
---  - If a register goes dead, and then becomes live again, the usages
---    of the disjoint live range don't count towards the original range.
---
---          a = 1; // used once
---          b = a;
---          a = 2; // used once
---          c = a;
---
---  - A register may be used multiple times, but these all reside in
---    different control paths, such that any given execution only uses
---    it once. In that case, the usage count may still be 1.
---
---          a = 1; // used once
---          if (b) {
---              c = a + 3;
---          } else {
---              c = a + 1;
---          }
---
---    This policy corresponds to an inlining strategy that does not
---    duplicate computation but may increase binary size.
---
---  - If we naively implement a usage count, we have a counting to
---    infinity problem across joins.  Furthermore, knowing that
---    something is used 2 or more times in one runtime execution isn't
---    particularly useful for optimizations (inlining may be beneficial,
---    but there's no way of knowing that without register pressure
---    information.)
---
---          while (...) {
---              // first iteration, b used once
---              // second iteration, b used twice
---              // third iteration ...
---              a = b;
---          }
---          // b used zero times
---
---    There is an orthogonal question, which is that for every runtime
---    execution, the register may be used only once, but if we inline it
---    in every conditional path, the binary size might increase a lot.
---    But tracking this information would be tricky, because it violates
---    the finite lattice restriction Hoopl requires for termination;
---    we'd thus need to supply an alternate proof, which is probably
---    something we should defer until we actually have an optimization
---    that would take advantage of this.  (This might also interact
---    strangely with liveness information.)
---
---          a = ...;
---          // a is used one time, but in X different paths
---          case (b) of
---              1 -> ... a ...
---              2 -> ... a ...
---              3 -> ... a ...
---              ...
---
---  - Memory stores to local register slots (CmmStore (CmmStackSlot
---    (LocalReg _) 0) _) have similar behavior to local registers,
---    in that these locations are all disjoint from each other.  Thus,
---    we attempt to inline them too. Note that because these are only
---    generated as part of the spilling process, most of the time this
---    will refer to a local register and the assignment will immediately
---    die on the subsequent call.  However, if we manage to replace that
---    local register with a memory location, it means that we've managed
---    to preserve a value on the stack without having to move it to
---    another memory location again!  We collect usage information just
---    to be safe in case extra computation is involved.
-
-data RegUsage = SingleUse | ManyUse
-    deriving (Ord, Eq, Show)
--- Absence in map = ZeroUse
-
-{-
--- minBound is bottom, maxBound is top, least-upper-bound is max
--- ToDo: Put this in Hoopl.  Note that this isn't as useful as I
--- originally hoped, because you usually want to leave out the bottom
--- element when you have things like this put in maps.  Maybe f is
--- useful on its own as a combining function.
-boundedOrdLattice :: (Bounded a, Ord a) => String -> DataflowLattice a
-boundedOrdLattice n = DataflowLattice n minBound f
-    where f _ (OldFact x) (NewFact y)
-            | x >= y    = (NoChange,   x)
-            | otherwise = (SomeChange, y)
--}
-
--- Custom node type we'll rewrite to.  CmmAssign nodes to local
--- registers are replaced with AssignLocal nodes.
-data WithRegUsage n e x where
-    -- Plain will not contain CmmAssign nodes immediately after
-    -- transformation, but as we rewrite assignments, we may have
-    -- assignments here: these are assignments that should not be
-    -- rewritten!
-    Plain       :: n e x -> WithRegUsage n e x
-    AssignLocal :: LocalReg -> CmmExpr -> RegUsage -> WithRegUsage n O O
-
-instance UserOfRegs LocalReg (n e x) => UserOfRegs LocalReg (WithRegUsage n e x) where
-    foldRegsUsed dflags f z (Plain n) = foldRegsUsed dflags f z n
-    foldRegsUsed dflags f z (AssignLocal _ e _) = foldRegsUsed dflags f z e
-
-instance DefinerOfRegs LocalReg (n e x) => DefinerOfRegs LocalReg (WithRegUsage n e x) where
-    foldRegsDefd dflags f z (Plain n) = foldRegsDefd dflags f z n
-    foldRegsDefd dflags f z (AssignLocal r _ _) = foldRegsDefd dflags f z r
-
-instance NonLocal n => NonLocal (WithRegUsage n) where
-    entryLabel (Plain n) = entryLabel n
-    successors (Plain n) = successors n
-
-liftRegUsage :: Graph n e x -> Graph (WithRegUsage n) e x
-liftRegUsage = mapGraph Plain
-
-eraseRegUsage :: Graph (WithRegUsage CmmNode) e x -> Graph CmmNode e x
-eraseRegUsage = mapGraph f
-    where f :: WithRegUsage CmmNode e x -> CmmNode e x
-          f (AssignLocal l e _) = CmmAssign (CmmLocal l) e
-          f (Plain n) = n
-
-type UsageMap = UniqFM RegUsage
-
-usageLattice :: DataflowLattice UsageMap
-usageLattice = DataflowLattice "usage counts for registers" emptyUFM (joinUFM f)
-    where f _ (OldFact x) (NewFact y)
-            | x >= y    = (NoChange,   x)
-            | otherwise = (SomeChange, y)
-
--- We reuse the names 'gen' and 'kill', although we're doing something
--- slightly different from the Dragon Book
-usageTransfer :: DynFlags -> BwdTransfer (WithRegUsage CmmNode) UsageMap
-usageTransfer dflags = mkBTransfer3 first middle last
-    where first _ f = f
-          middle :: WithRegUsage CmmNode O O -> UsageMap -> UsageMap
-          middle n f = gen_kill n f
-          last :: WithRegUsage CmmNode O C -> FactBase UsageMap -> UsageMap
-          -- Checking for CmmCall/CmmForeignCall is unnecessary, because
-          -- spills/reloads have already occurred by the time we do this
-          -- analysis.
-          -- XXX Deprecated warning is puzzling: what label are we
-          -- supposed to use?
-          -- ToDo: With a bit more cleverness here, we can avoid
-          -- disappointment and heartbreak associated with the inability
-          -- to inline into CmmCall and CmmForeignCall by
-          -- over-estimating the usage to be ManyUse.
-          last n f = gen_kill n (joinOutFacts usageLattice n f)
-          gen_kill :: WithRegUsage CmmNode e x -> UsageMap -> UsageMap
-          gen_kill a = gen a . kill a
-          gen :: WithRegUsage CmmNode e x -> UsageMap -> UsageMap
-          gen  a f = foldLocalRegsUsed dflags increaseUsage f a
-          kill :: WithRegUsage CmmNode e x -> UsageMap -> UsageMap
-          kill a f = foldLocalRegsDefd dflags delFromUFM f a
-          increaseUsage f r = addToUFM_C combine f r SingleUse
-            where combine _ _ = ManyUse
-
-usageRewrite :: BwdRewrite UniqSM (WithRegUsage CmmNode) UsageMap
-usageRewrite = mkBRewrite3 first middle last
-    where first  _ _ = return Nothing
-          middle :: Monad m => WithRegUsage CmmNode O O -> UsageMap -> m (Maybe (Graph (WithRegUsage CmmNode) O O))
-          middle (Plain (CmmAssign (CmmLocal l) e)) f
-                     = return . Just
-                     $ case lookupUFM f l of
-                            Nothing    -> emptyGraph
-                            Just usage -> mkMiddle (AssignLocal l e usage)
-          middle _ _ = return Nothing
-          last   _ _ = return Nothing
-
-type CmmGraphWithRegUsage = GenCmmGraph (WithRegUsage CmmNode)
-annotateUsage :: DynFlags -> CmmGraph -> UniqSM (CmmGraphWithRegUsage)
-annotateUsage dflags vanilla_g =
-    let g = modifyGraph liftRegUsage vanilla_g
-    in liftM fst $ dataflowPassBwd g [(g_entry g, fact_bot usageLattice)] $
-                                   analRewBwd usageLattice (usageTransfer dflags) usageRewrite
-
-----------------------------------------------------------------
---- Assignment tracking
-
--- The idea is to maintain a map of local registers do expressions,
--- such that the value of that register is the same as the value of that
--- expression at any given time.  We can then do several things,
--- as described by Assignment.
-
--- Assignment describes the various optimizations that are valid
--- at a given point in the program.
-data Assignment =
--- This assignment can always be inlined.  It is cheap or single-use.
-                  AlwaysInline CmmExpr
--- This assignment should be sunk down to its first use.  (This will
--- increase code size if the register is used in multiple control flow
--- paths, but won't increase execution time, and the reduction of
--- register pressure is worth it, I think.)
-                | AlwaysSink CmmExpr
--- We cannot safely optimize occurrences of this local register. (This
--- corresponds to top in the lattice structure.)
-                | NeverOptimize
-
--- Extract the expression that is being assigned to
-xassign :: Assignment -> Maybe CmmExpr
-xassign (AlwaysInline e) = Just e
-xassign (AlwaysSink e)   = Just e
-xassign NeverOptimize    = Nothing
-
--- Extracts the expression, but only if they're the same constructor
-xassign2 :: (Assignment, Assignment) -> Maybe (CmmExpr, CmmExpr)
-xassign2 (AlwaysInline e, AlwaysInline e') = Just (e, e')
-xassign2 (AlwaysSink e, AlwaysSink e')     = Just (e, e')
-xassign2 _ = Nothing
-
--- Note: We'd like to make decisions about "not optimizing" as soon as
--- possible, because this will make running the transfer function more
--- efficient.
-type AssignmentMap = UniqFM Assignment
-
-assignmentLattice :: DataflowLattice AssignmentMap
-assignmentLattice = DataflowLattice "assignments for registers" emptyUFM (joinUFM add)
-    where add _ (OldFact old) (NewFact new)
-            = case (old, new) of
-                (NeverOptimize, _) -> (NoChange,   NeverOptimize)
-                (_, NeverOptimize) -> (SomeChange, NeverOptimize)
-                (xassign2 -> Just (e, e'))
-                    | e == e'   -> (NoChange, old)
-                    | otherwise -> (SomeChange, NeverOptimize)
-                _ -> (SomeChange, NeverOptimize)
-
--- Deletes sinks from assignment map, because /this/ is the place
--- where it will be sunk to.
-deleteSinks :: UserOfRegs LocalReg n => DynFlags -> n -> AssignmentMap -> AssignmentMap
-deleteSinks dflags n m = foldLocalRegsUsed dflags (adjustUFM f) m n
-  where f (AlwaysSink _) = NeverOptimize
-        f old = old
-
--- Invalidates any expressions that use a register.
-invalidateUsersOf :: CmmReg -> AssignmentMap -> AssignmentMap
--- foldUFM_Directly :: (Unique -> elt -> a -> a) -> a -> UniqFM elt -> a
-invalidateUsersOf reg m = foldUFM_Directly f m m -- [foldUFM performance]
-    where f u (xassign -> Just e) m | reg `regUsedIn` e = addToUFM_Directly m u NeverOptimize
-          f _ _ m = m
-{- This requires the entire spine of the map to be continually rebuilt,
- - which causes crazy memory usage!
-invalidateUsersOf reg = mapUFM (invalidateUsers' reg)
-  where invalidateUsers' reg (xassign -> Just e) | reg `regUsedIn` e = NeverOptimize
-        invalidateUsers' _ old = old
--}
-
--- Note [foldUFM performance]
--- These calls to fold UFM no longer leak memory, but they do cause
--- pretty killer amounts of allocation.  So they'll be something to
--- optimize; we need an algorithmic change to prevent us from having to
--- traverse the /entire/ map continually.
-
-middleAssignment :: DynFlags -> WithRegUsage CmmNode O O -> AssignmentMap
-                 -> AssignmentMap
-
--- Algorithm for annotated assignments:
---  1. Delete any sinking assignments that were used by this instruction
---  2. Add the assignment to our list of valid local assignments with
---     the correct optimization policy.
---  3. Look for all assignments that reference that register and
---     invalidate them.
-middleAssignment dflags n@(AssignLocal r e usage) assign
-    = invalidateUsersOf (CmmLocal r) . add . deleteSinks dflags n $ assign
-      where add m = addToUFM m r
-                  $ case usage of
-                        SingleUse -> AlwaysInline e
-                        ManyUse   -> decide e
-            decide CmmLit{}       = AlwaysInline e
-            decide CmmReg{}       = AlwaysInline e
-            decide CmmLoad{}      = AlwaysSink e
-            decide CmmStackSlot{} = AlwaysSink e
-            decide CmmMachOp{}    = AlwaysSink e
-            -- We'll always inline simple operations on the global
-            -- registers, to reduce register pressure: Sp - 4 or Hp - 8
-            -- EZY: Justify this optimization more carefully.
-            decide CmmRegOff{}    = AlwaysInline e
-
--- Algorithm for unannotated assignments of global registers:
--- 1. Delete any sinking assignments that were used by this instruction
--- 2. Look for all assignments that reference this register and
---    invalidate them.
-middleAssignment dflags (Plain n@(CmmAssign reg@(CmmGlobal _) _)) assign
-    = invalidateUsersOf reg . deleteSinks dflags n $ assign
-
--- Algorithm for unannotated assignments of *local* registers: do
--- nothing (it's a reload, so no state should have changed)
-middleAssignment _ (Plain (CmmAssign (CmmLocal _) _)) assign = assign
-
--- Algorithm for stores:
---  1. Delete any sinking assignments that were used by this instruction
---  2. Look for all assignments that load from memory locations that
---     were clobbered by this store and invalidate them.
-middleAssignment dflags (Plain n@(CmmStore lhs rhs)) assign
-    = let m = deleteSinks dflags n assign
-      in foldUFM_Directly f m m -- [foldUFM performance]
-      where f u (xassign -> Just x) m | clobbers dflags (lhs, rhs) (u, x) = addToUFM_Directly m u NeverOptimize
-            f _ _ m = m
-{- Also leaky
-    = mapUFM_Directly p . deleteSinks n $ assign
-      -- ToDo: There's a missed opportunity here: even if a memory
-      -- access we're attempting to sink gets clobbered at some
-      -- location, it's still /better/ to sink it to right before the
-      -- point where it gets clobbered.  How might we do this?
-      -- Unfortunately, it's too late to change the assignment...
-      where p r (xassign -> Just x) | (lhs, rhs) `clobbers` (r, x) = NeverOptimize
-            p _ old = old
--}
-
--- Assumption: Unsafe foreign calls don't clobber memory
--- Since foreign calls clobber caller saved registers, we need
--- invalidate any assignments that reference those global registers.
--- This is kind of expensive. (One way to optimize this might be to
--- store extra information about expressions that allow this and other
--- checks to be done cheaply.)
-middleAssignment dflags (Plain n@(CmmUnsafeForeignCall{})) assign
-    = deleteCallerSaves (foldLocalRegsDefd dflags (\m r -> addToUFM m r NeverOptimize) (deleteSinks dflags n assign) n)
-    where deleteCallerSaves m = foldUFM_Directly f m m
-          f u (xassign -> Just x) m | wrapRecExpf g x False = addToUFM_Directly m u NeverOptimize
-          f _ _ m = m
-          g (CmmReg (CmmGlobal r)) _      | callerSaves platform r = True
-          g (CmmRegOff (CmmGlobal r) _) _ | callerSaves platform r = True
-          g _ b = b
-          platform = targetPlatform dflags
-
-middleAssignment _ (Plain (CmmComment {})) assign
-    = assign
-
--- Assumptions:
---  * Writes using Hp do not overlap with any other memory locations
---    (An important invariant being relied on here is that we only ever
---    use Hp to allocate values on the heap, which appears to be the
---    case given hpReg usage, and that our heap writing code doesn't
---    do anything stupid like overlapping writes.)
---  * Stack slots do not overlap with any other memory locations
---  * Stack slots for different areas do not overlap
---  * Stack slots within the same area and different offsets may
---    overlap; we need to do a size check (see 'overlaps').
---  * Register slots only overlap with themselves.  (But this shouldn't
---    happen in practice, because we'll fail to inline a reload across
---    the next spill.)
---  * Non stack-slot stores always conflict with each other.  (This is
---    not always the case; we could probably do something special for Hp)
-clobbers :: DynFlags
-         -> (CmmExpr, CmmExpr) -- (lhs, rhs) of clobbering CmmStore
-         -> (Unique,  CmmExpr) -- (register, expression) that may be clobbered
-         -> Bool
-clobbers _ (CmmRegOff (CmmGlobal Hp) _, _) (_, _) = False
-clobbers _ (CmmReg (CmmGlobal Hp), _) (_, _) = False
--- ToDo: Also catch MachOp case
-clobbers _ (ss@CmmStackSlot{}, CmmReg (CmmLocal r)) (u, CmmLoad (ss'@CmmStackSlot{}) _)
-    | getUnique r == u, ss == ss' = False -- No-op on the stack slot (XXX: Do we need this special case?)
-clobbers dflags (CmmStackSlot a o, rhs) (_, expr) = f expr
-    where f (CmmLoad (CmmStackSlot a' o') t)
-            = (a, o, widthInBytes (cmmExprWidth dflags rhs)) `overlaps` (a', o', widthInBytes (typeWidth t))
-          f (CmmLoad e _)    = containsStackSlot e
-          f (CmmMachOp _ es) = or (map f es)
-          f _                = False
-          -- Maybe there's an invariant broken if this actually ever
-          -- returns True
-          containsStackSlot (CmmLoad{})      = True -- load of a load, all bets off
-          containsStackSlot (CmmMachOp _ es) = or (map containsStackSlot es)
-          containsStackSlot (CmmStackSlot{}) = True
-          containsStackSlot _ = False
-clobbers _ _ (_, e) = f e
-    where f (CmmLoad (CmmStackSlot _ _) _) = False
-          f (CmmLoad{}) = True -- conservative
-          f (CmmMachOp _ es) = or (map f es)
-          f _ = False
-
--- Check for memory overlapping.
--- Diagram:
---      4      8     12
---      s -w-  o
---      [ I32  ]
---      [    F64     ]
---      s'   -w'-    o'
-type CallSubArea = (Area, Int, Int) -- area, offset, width
-overlaps :: CallSubArea -> CallSubArea -> Bool
-overlaps (a, _, _) (a', _, _) | a /= a' = False
-overlaps (_, o, w) (_, o', w') =
-    let s  = o  - w
-        s' = o' - w'
-    in (s' < o) && (s < o) -- Not LTE, because [ I32  ][ I32  ] is OK
-
-lastAssignment :: DynFlags -> WithRegUsage CmmNode O C -> AssignmentMap -> [(Label, AssignmentMap)]
-lastAssignment _ (Plain (CmmCall _ (Just k) _ _ _ _)) assign = [(k, invalidateVolatile k assign)]
-lastAssignment _ (Plain (CmmForeignCall {succ=k}))  assign = [(k, invalidateVolatile k assign)]
-lastAssignment dflags l assign = map (\id -> (id, deleteSinks dflags l assign)) $ successors l
-
--- Invalidates any expressions that have volatile contents: essentially,
--- all terminals volatile except for literals and loads of stack slots
--- that do not correspond to the call area for 'k' (the current call
--- area is volatile because overflow return parameters may be written
--- there.)
--- Note: mapUFM could be expensive, but hopefully block boundaries
--- aren't too common.  If it is a problem, replace with something more
--- clever.
-invalidateVolatile :: BlockId -> AssignmentMap -> AssignmentMap
-invalidateVolatile k m = mapUFM p m
-  where p (AlwaysInline e) = if exp e then AlwaysInline e else NeverOptimize
-            where exp CmmLit{} = True
-                  exp (CmmLoad (CmmStackSlot (Young k') _) _)
-                    | k' == k = False
-                  exp (CmmLoad (CmmStackSlot _ _) _) = True
-                  exp (CmmMachOp _ es) = and (map exp es)
-                  exp _ = False
-        p _ = NeverOptimize -- probably shouldn't happen with AlwaysSink
-
-assignmentTransfer :: DynFlags
-                   -> FwdTransfer (WithRegUsage CmmNode) AssignmentMap
-assignmentTransfer dflags
-    = mkFTransfer3 (flip const)
-                   (middleAssignment dflags)
-                   ((mkFactBase assignmentLattice .) . lastAssignment dflags)
-
--- Note [Soundness of inlining]
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- In the Hoopl paper, the soundness condition on rewrite functions is
--- described as follows:
---
---      "If it replaces a node n by a replacement graph g, then g must
---      be observationally equivalent to n under the assumptions
---      expressed by the incoming dataflow fact f.  Moreover, analysis of
---      g must produce output fact(s) that are at least as informative
---      as the fact(s) produced by applying the transfer function to n."
---
--- We consider the second condition in more detail here.  It says given
--- the rewrite R(n, f) = g, then for any incoming fact f' consistent
--- with f (f' >= f), then running the transfer function T(f', n) <= T(f', g).
--- For inlining this is not necessarily the case:
---
---  n = "x = a + 2"
---  f = f' = {a = y}
---  g = "x = y + 2"
---  T(f', n) = {x = a + 2, a = y}
---  T(f', g) = {x = y + 2, a = y}
---
--- y + 2 and a + 2 are not obviously comparable, and a naive
--- implementation of the lattice would say they are incomparable.
--- At best, this means we may be over-conservative, at worst, it means
--- we may not terminate.
---
--- However, in the original Lerner-Grove-Chambers paper, soundness and
--- termination are separated, and only equivalence of facts is required
--- for soundness.  Monotonicity of the transfer function is not required
--- for termination (as the calculation of least-upper-bound prevents
--- this from being a problem), but it means we won't necessarily find
--- the least-fixed point.
-
--- Note [Coherency of annotations]
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- Is it possible for our usage annotations to become invalid after we
--- start performing transformations?  As the usage info only provides
--- an upper bound, we only need to consider cases where the usages of
--- a register may increase due to transformations--e.g. any reference
--- to a local register in an AlwaysInline or AlwaysSink instruction, whose
--- originating assignment was single use (we don't care about the
--- many use case, because it is the top of the lattice).  But such a
--- case is not possible, because we always inline any single use
--- register.  QED.
---
--- TODO: A useful lint option would be to check this invariant that
--- there is never a local register in the assignment map that is
--- single-use.
-
--- Note [Soundness of store rewriting]
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- Its soundness depends on the invariant that no assignment is made to
--- the local register before its store is accessed.  This is clearly
--- true with unoptimized spill-reload code, and as the store will always
--- be rewritten first (if possible), there is no chance of it being
--- propagated down before getting written (possibly with incorrect
--- values from the assignment map, due to reassignment of the local
--- register.)  This is probably not locally sound.
-
-assignmentRewrite :: DynFlags -> FwdRewrite UniqSM (WithRegUsage CmmNode) AssignmentMap
-assignmentRewrite dflags = mkFRewrite3 first middle last
-    where
-        first _ _ = return Nothing
-        middle :: WithRegUsage CmmNode O O -> AssignmentMap -> GenCmmReplGraph (WithRegUsage CmmNode) O O
-        middle (Plain m) assign = return $ rewrite assign (precompute assign m) mkMiddle m
-        middle (AssignLocal l e u) assign = return $ rewriteLocal assign (precompute assign (CmmAssign (CmmLocal l) e)) l e u
-        last (Plain l) assign = return $ rewrite assign (precompute assign l) mkLast l
-        -- Tuple is (inline?, reloads for sinks)
-        precompute :: AssignmentMap -> CmmNode O x -> (Bool, [WithRegUsage CmmNode O O])
-        precompute assign n = foldLocalRegsUsed dflags f (False, []) n -- duplicates are harmless
-            where f (i, l) r = case lookupUFM assign r of
-                                Just (AlwaysSink e)   -> (i, (Plain (CmmAssign (CmmLocal r) e)):l)
-                                Just (AlwaysInline _) -> (True, l)
-                                Just NeverOptimize    -> (i, l)
-                                -- This case can show up when we have
-                                -- limited optimization fuel.
-                                Nothing -> (i, l)
-        rewrite :: AssignmentMap
-                -> (Bool, [WithRegUsage CmmNode O O])
-                -> (WithRegUsage CmmNode O x -> Graph (WithRegUsage CmmNode) O x)
-                -> CmmNode O x
-                -> Maybe (Graph (WithRegUsage CmmNode) O x)
-        rewrite _ (False, []) _ _ = Nothing
-        -- Note [CmmCall Inline Hack]
-        -- Conservative hack: don't do any inlining on what will
-        -- be translated into an OldCmm CmmCalls, since the code
-        -- produced here tends to be unproblematic and I need to write
-        -- lint passes to ensure that we don't put anything in the
-        -- arguments that could be construed as a global register by
-        -- some later translation pass.  (For example, slots will turn
-        -- into dereferences of Sp).  See [Register parameter passing].
-        -- ToDo: Fix this up to only bug out if all inlines were for
-        -- CmmExprs with global registers (we can't use the
-        -- straightforward mapExpDeep call, in this case.) ToDo: We miss
-        -- an opportunity here, where all possible inlinings should
-        -- instead be sunk.
-        rewrite _ (True, []) _ n | not (inlinable n) = Nothing -- see [CmmCall Inline Hack]
-        rewrite assign (i, xs) mk n = Just $ mkMiddles xs <*> mk (Plain (inline i assign n))
-
-        rewriteLocal :: AssignmentMap
-                     -> (Bool, [WithRegUsage CmmNode O O])
-                     -> LocalReg -> CmmExpr -> RegUsage
-                     -> Maybe (Graph (WithRegUsage CmmNode) O O)
-        rewriteLocal _ (False, []) _ _ _ = Nothing
-        rewriteLocal assign (i, xs) l e u = Just $ mkMiddles xs <*> mkMiddle n'
-            where n' = AssignLocal l e' u
-                  e' = if i then wrapRecExp (inlineExp assign) e else e
-            -- inlinable check omitted, since we can always inline into
-            -- assignments.
-
-        inline :: Bool -> AssignmentMap -> CmmNode e x -> CmmNode e x
-        inline False _ n = n
-        inline True  _ n | not (inlinable n) = n -- see [CmmCall Inline Hack]
-        inline True assign n = mapExpDeep (inlineExp assign) n
-
-        inlineExp assign old@(CmmReg (CmmLocal r))
-          = case lookupUFM assign r of
-              Just (AlwaysInline x) -> x
-              _ -> old
-        inlineExp assign old@(CmmRegOff (CmmLocal r) i)
-          = case lookupUFM assign r of
-              Just (AlwaysInline x) ->
-                case x of
-                    (CmmRegOff r' i') -> CmmRegOff r' (i + i')
-                    _ -> CmmMachOp (MO_Add rep) [x, CmmLit (CmmInt (fromIntegral i) rep)]
-                          where rep = typeWidth (localRegType r)
-              _ -> old
-        -- See Note [Soundness of store rewriting]
-        inlineExp _ old = old
-
-        inlinable :: CmmNode e x -> Bool
-        inlinable (CmmCall{}) = False
-        inlinable (CmmForeignCall{}) = False
-        inlinable (CmmUnsafeForeignCall{}) = False
-        inlinable _ = True
-
--- Need to interleave this with inlining, because machop folding results
--- in literals, which we can inline more aggressively, and inlining
--- gives us opportunities for more folding.  However, we don't need any
--- facts to do MachOp folding.
-machOpFoldRewrite :: DynFlags -> FwdRewrite UniqSM (WithRegUsage CmmNode) a
-machOpFoldRewrite dflags = mkFRewrite3 first middle last
-  where first _ _ = return Nothing
-        middle :: WithRegUsage CmmNode O O -> a -> GenCmmReplGraph (WithRegUsage CmmNode) O O
-        middle (Plain m) _ = return (fmap (mkMiddle . Plain) (foldNode m))
-        middle (AssignLocal l e r) _ = return (fmap f (wrapRecExpM foldExp e))
-            where f e' = mkMiddle (AssignLocal l e' r)
-        last   :: WithRegUsage CmmNode O C -> a -> GenCmmReplGraph (WithRegUsage CmmNode) O C
-        last (Plain l) _ = return (fmap (mkLast . Plain) (foldNode l))
-        foldNode :: CmmNode e x -> Maybe (CmmNode e x)
-        foldNode n = mapExpDeepM foldExp n
-        foldExp (CmmMachOp op args) = cmmMachOpFoldM dflags op args
-        foldExp _ = Nothing
-
--- ToDo: Outputable instance for UsageMap and AssignmentMap
diff --git a/compiler/ghc.cabal.in b/compiler/ghc.cabal.in
index a5d9785a43..f70a8e4b30 100644
--- a/compiler/ghc.cabal.in
+++ b/compiler/ghc.cabal.in
@@ -183,7 +183,6 @@ Library
         CmmOpt
         CmmParse
         CmmProcPoint
-        CmmRewriteAssignments
         CmmSink
         CmmType
         CmmUtils