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.

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
 

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

compiler/ghc.cabal.in

@@ -183,7 +183,6 @@ Library
         CmmOpt
         CmmParse
         CmmProcPoint
-        CmmRewriteAssignments
         CmmSink
         CmmType
         CmmUtils