-- -----------------------------------------------------------------------------
-- (c) The University of Glasgow 1993-2004
-- This is the top-level module in the native code generator.
-- -----------------------------------------------------------------------------

{-# OPTIONS -w #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details

module AsmCodeGen ( nativeCodeGen ) where

#include "HsVersions.h"
#include "nativeGen/NCG.h"

#if   alpha_TARGET_ARCH
import Alpha.CodeGen
import Alpha.Regs
import Alpha.RegInfo
import Alpha.Instr

#elif i386_TARGET_ARCH || x86_64_TARGET_ARCH
import X86.CodeGen
import X86.Regs
import X86.RegInfo
import X86.Instr
import X86.Ppr

#elif sparc_TARGET_ARCH
import SPARC.CodeGen
import SPARC.Regs
import SPARC.Instr
import SPARC.Ppr
import SPARC.ShortcutJump

#elif powerpc_TARGET_ARCH
import PPC.CodeGen
import PPC.Cond
import PPC.Regs
import PPC.RegInfo
import PPC.Instr
import PPC.Ppr

#error "AsmCodeGen: unknown architecture"


import RegAlloc.Liveness
import qualified RegAlloc.Linear.Main		as Linear

import qualified GraphColor			as Color
import qualified RegAlloc.Graph.Main		as Color
import qualified RegAlloc.Graph.Stats		as Color
import qualified RegAlloc.Graph.Coalesce	as Color
import qualified RegAlloc.Graph.TrivColorable	as Color

import qualified SPARC.CodeGen.Expand		as SPARC

import TargetReg
import Platform
import Instruction
import PIC
import Reg
import RegClass
import NCGMonad

import Cmm
import CmmOpt		( cmmMiniInline, cmmMachOpFold )
import PprCmm
import CLabel
import State

import UniqFM
import Unique		( Unique, getUnique )
import UniqSupply
import DynFlags
#if powerpc_TARGET_ARCH
import StaticFlags	( opt_Static, opt_PIC )
import Util
import Config           ( cProjectVersion )
import Module

import Digraph
import qualified Pretty
import BufWrite
import Outputable
import FastString
import UniqSet
import ErrUtils

--import OrdList

import Data.List
import Data.Int
import Data.Word
import Data.Bits
import Data.Maybe
import GHC.Exts
import Control.Monad
import System.IO

The native-code generator has machine-independent and
machine-dependent modules.

This module ("AsmCodeGen") is the top-level machine-independent
module.  Before entering machine-dependent land, we do some
machine-independent optimisations (defined below) on the

We convert to the machine-specific 'Instr' datatype with
'cmmCodeGen', assuming an infinite supply of registers.  We then use
a machine-independent register allocator ('regAlloc') to rejoin
reality.  Obviously, 'regAlloc' has machine-specific helper
functions (see about "RegAllocInfo" below).

Finally, we order the basic blocks of the function so as to minimise
the number of jumps between blocks, by utilising fallthrough wherever

The machine-dependent bits break down as follows:

  * ["MachRegs"]  Everything about the target platform's machine
    registers (and immediate operands, and addresses, which tend to
    intermingle/interact with registers).

  * ["MachInstrs"]  Includes the 'Instr' datatype (possibly should
    have a module of its own), plus a miscellany of other things
    (e.g., 'targetDoubleSize', 'smStablePtrTable', ...)

  * ["MachCodeGen"]  is where 'Cmm' stuff turns into
    machine instructions.

  * ["PprMach"] 'pprInstr' turns an 'Instr' into text (well, really
    a 'Doc').

  * ["RegAllocInfo"] In the register allocator, we manipulate
    'MRegsState's, which are 'BitSet's, one bit per machine register.
    When we want to say something about a specific machine register
    (e.g., ``it gets clobbered by this instruction''), we set/unset
    its bit.  Obviously, we do this 'BitSet' thing for efficiency

    The 'RegAllocInfo' module collects together the machine-specific
    info needed to do register allocation.

   * ["RegisterAlloc"] The (machine-independent) register allocator.

-- -----------------------------------------------------------------------------
-- Top-level of the native codegen

nativeCodeGen :: DynFlags -> Handle -> UniqSupply -> [RawCmm] -> IO ()
nativeCodeGen dflags h us cmms
 = do
	let split_cmms	= concat $ map add_split cmms

        -- BufHandle is a performance hack.  We could hide it inside
        -- Pretty if it weren't for the fact that we do lots of little
        -- printDocs here (in order to do codegen in constant space).
        bufh <- newBufHandle h
 	(imports, prof) <- cmmNativeGens dflags bufh us split_cmms [] [] 0
        bFlush bufh

	let (native, colorStats, linearStats)
		= unzip3 prof

	-- dump native code
	dumpIfSet_dyn dflags
		Opt_D_dump_asm "Asm code"
		(vcat $ map (docToSDoc . pprNatCmmTop) $ concat native)

	-- dump global NCG stats for graph coloring allocator
	(case concat $ catMaybes colorStats of
	  []	-> return ()
	  stats	-> do	
	   	-- build the global register conflict graph
		let graphGlobal	
			= foldl Color.union Color.initGraph
			$ [ Color.raGraph stat
				| stat@Color.RegAllocStatsStart{} <- stats]
	   	dumpSDoc dflags Opt_D_dump_asm_stats "NCG stats"
			$ Color.pprStats stats graphGlobal

		dumpIfSet_dyn dflags
			Opt_D_dump_asm_conflicts "Register conflict graph"
			$ Color.dotGraph 
			$ graphGlobal)

	-- dump global NCG stats for linear allocator
	(case concat $ catMaybes linearStats of
		[]	-> return ()
		stats	-> dumpSDoc dflags Opt_D_dump_asm_stats "NCG stats"
				$ Linear.pprStats (concat native) stats)

	-- write out the imports
	Pretty.printDoc Pretty.LeftMode h
		$ makeImportsDoc dflags (concat imports)

	return	()

 where	add_split (Cmm tops)
		| dopt Opt_SplitObjs dflags = split_marker : tops
		| otherwise		    = tops

	split_marker = CmmProc [] mkSplitMarkerLabel [] (ListGraph [])

-- | Do native code generation on all these cmms.
cmmNativeGens dflags h us [] impAcc profAcc count
	= return (reverse impAcc, reverse profAcc)

cmmNativeGens dflags h us (cmm : cmms) impAcc profAcc count
 = do
 	(us', native, imports, colorStats, linearStats)
		<- cmmNativeGen dflags us cmm count

	Pretty.bufLeftRender h
		$ {-# SCC "pprNativeCode" #-} Pretty.vcat $ map pprNatCmmTop native

           -- carefully evaluate this strictly.  Binding it with 'let'
           -- and then using 'seq' doesn't work, because the let
           -- apparently gets inlined first.
	lsPprNative <- return $!
		if  dopt Opt_D_dump_asm       dflags
	         || dopt Opt_D_dump_asm_stats dflags
			then native
			else []

	count' <- return $! count + 1;

	-- force evaulation all this stuff to avoid space leaks
	seqString (showSDoc $ vcat $ map ppr imports) `seq` return ()

	cmmNativeGens dflags h us' cmms
			(imports : impAcc)
			((lsPprNative, colorStats, linearStats) : profAcc)

 where	seqString []		= ()
	seqString (x:xs)	= x `seq` seqString xs `seq` ()

-- | Complete native code generation phase for a single top-level chunk of Cmm.
--	Dumping the output of each stage along the way.
--	Global conflict graph and NGC stats
	:: DynFlags
	-> UniqSupply
	-> RawCmmTop					-- ^ the cmm to generate code for
	-> Int						-- ^ sequence number of this top thing
	-> IO	( UniqSupply
		, [NatCmmTop Instr]			-- native code
		, [CLabel]				-- things imported by this cmm
		, Maybe [Color.RegAllocStats Instr]	-- stats for the coloring register allocator
		, Maybe [Linear.RegAllocStats])		-- stats for the linear register allocators

cmmNativeGen dflags us cmm count
 = do

	-- rewrite assignments to global regs
 	let (fixed_cmm, usFix)	=
		{-# SCC "fixAssignsTop" #-}
		initUs us $ fixAssignsTop cmm

	-- cmm to cmm optimisations
	let (opt_cmm, imports) =
		{-# SCC "cmmToCmm" #-}
		cmmToCmm dflags fixed_cmm

	dumpIfSet_dyn dflags
		Opt_D_dump_opt_cmm "Optimised Cmm"
		(pprCmm $ Cmm [opt_cmm])

	-- generate native code from cmm
	let ((native, lastMinuteImports), usGen) =
		{-# SCC "genMachCode" #-}
		initUs usFix $ genMachCode dflags opt_cmm

	dumpIfSet_dyn dflags
		Opt_D_dump_asm_native "Native code"
		(vcat $ map (docToSDoc . pprNatCmmTop) native)

	-- tag instructions with register liveness information
	let (withLiveness, usLive) =
		{-# SCC "regLiveness" #-}
		initUs usGen $ mapUs regLiveness native

	dumpIfSet_dyn dflags
		Opt_D_dump_asm_liveness "Liveness annotations added"
		(vcat $ map ppr withLiveness)

	-- allocate registers
	(alloced, usAlloc, ppr_raStatsColor, ppr_raStatsLinear) <-
	 if ( dopt Opt_RegsGraph dflags
	   || dopt Opt_RegsIterative dflags)
	  then do
	  	-- the regs usable for allocation
		let (alloc_regs :: UniqFM (UniqSet RealReg))
			= foldr (\r -> plusUFM_C unionUniqSets
					$ unitUFM (targetClassOfRealReg r) (unitUniqSet r))
			$ allocatableRegs

		-- do the graph coloring register allocation
		let ((alloced, regAllocStats), usAlloc)
			= {-# SCC "RegAlloc" #-}
			  initUs usLive
			  $ Color.regAlloc
				(mkUniqSet [0..maxSpillSlots])

		-- dump out what happened during register allocation
		dumpIfSet_dyn dflags
			Opt_D_dump_asm_regalloc "Registers allocated"
			(vcat $ map (docToSDoc . pprNatCmmTop) alloced)

		dumpIfSet_dyn dflags
			Opt_D_dump_asm_regalloc_stages "Build/spill stages"
			(vcat 	$ map (\(stage, stats)
					-> text "# --------------------------"
					$$ text "#  cmm " <> int count <> text " Stage " <> int stage
					$$ ppr stats)
				$ zip [0..] regAllocStats)

		let mPprStats =
			if dopt Opt_D_dump_asm_stats dflags
			 then Just regAllocStats else Nothing

		-- force evaluation of the Maybe to avoid space leak
		mPprStats `seq` return ()

		return	( alloced, usAlloc
			, mPprStats
			, Nothing)

	  else do
	  	-- do linear register allocation
		let ((alloced, regAllocStats), usAlloc) 
			= {-# SCC "RegAlloc" #-}
  			  initUs usLive
 			  $ liftM unzip
			  $ mapUs Linear.regAlloc withLiveness

		dumpIfSet_dyn dflags
			Opt_D_dump_asm_regalloc "Registers allocated"
			(vcat $ map (docToSDoc . pprNatCmmTop) alloced)

		let mPprStats =
			if dopt Opt_D_dump_asm_stats dflags
			 then Just (catMaybes regAllocStats) else Nothing

		-- force evaluation of the Maybe to avoid space leak
		mPprStats `seq` return ()

		return	( alloced, usAlloc
			, Nothing
			, mPprStats)

	---- shortcut branches
	let shorted	=
	 	{-# SCC "shortcutBranches" #-}
	 	shortcutBranches dflags alloced

	---- sequence blocks
	let sequenced	=
	 	{-# SCC "sequenceBlocks" #-}
	 	map sequenceTop shorted

	---- x86fp_kludge
	let kludged =
#if i386_TARGET_ARCH
	 	{-# SCC "x86fp_kludge" #-}
	 	map x86fp_kludge sequenced

	---- expansion of SPARC synthetic instrs
#if sparc_TARGET_ARCH
	let expanded = 
		{-# SCC "sparc_expand" #-}
		map SPARC.expandTop kludged

	dumpIfSet_dyn dflags
		Opt_D_dump_asm_expanded "Synthetic instructions expanded"
		(vcat $ map (docToSDoc . pprNatCmmTop) expanded)
	let expanded = 

	return 	( usAlloc
		, expanded
		, lastMinuteImports ++ imports
		, ppr_raStatsColor
		, ppr_raStatsLinear)

#if i386_TARGET_ARCH
x86fp_kludge :: NatCmmTop Instr -> NatCmmTop Instr
x86fp_kludge top@(CmmData _ _) = top
x86fp_kludge top@(CmmProc info lbl params (ListGraph code)) = 
	CmmProc info lbl params (ListGraph $ i386_insert_ffrees code)

-- | Build a doc for all the imports.
makeImportsDoc :: DynFlags -> [CLabel] -> Pretty.Doc
makeImportsDoc dflags imports
 = dyld_stubs imports

                -- On recent versions of Darwin, the linker supports
                -- dead-stripping of code and data on a per-symbol basis.
                -- There's a hack to make this work in PprMach.pprNatCmmTop.
            Pretty.$$ Pretty.text ".subsections_via_symbols"
                -- On recent GNU ELF systems one can mark an object file
                -- as not requiring an executable stack. If all objects
                -- linked into a program have this note then the program
                -- will not use an executable stack, which is good for
                -- security. GHC generated code does not need an executable
                -- stack so add the note in:
            Pretty.$$ Pretty.text ".section .note.GNU-stack,\"\",@progbits"
#if !defined(darwin_TARGET_OS)
                -- And just because every other compiler does, lets stick in
		-- an identifier directive: .ident "GHC x.y.z"
	    Pretty.$$ let compilerIdent = Pretty.text "GHC" Pretty.<+>
	                                  Pretty.text cProjectVersion
                       in Pretty.text ".ident" Pretty.<+>
                          Pretty.doubleQuotes compilerIdent

	-- Generate "symbol stubs" for all external symbols that might
	-- come from a dynamic library.
	dyld_stubs :: [CLabel] -> Pretty.Doc
{-      dyld_stubs imps = Pretty.vcat $ map pprDyldSymbolStub $
				    map head $ group $ sort imps-}

	arch	= platformArch	$ targetPlatform dflags
	os	= platformOS	$ targetPlatform dflags
	-- (Hack) sometimes two Labels pretty-print the same, but have
	-- different uniques; so we compare their text versions...
	dyld_stubs imps
		| needImportedSymbols arch os
		= Pretty.vcat $
			(pprGotDeclaration arch os :) $
			map ( pprImportedSymbol arch os . fst . head) $
			groupBy (\(_,a) (_,b) -> a == b) $
			sortBy (\(_,a) (_,b) -> compare a b) $
			map doPpr $
		| otherwise
		= Pretty.empty

	doPpr lbl = (lbl, Pretty.render $ pprCLabel lbl astyle)
	astyle = mkCodeStyle AsmStyle

-- -----------------------------------------------------------------------------
-- Sequencing the basic blocks

-- Cmm BasicBlocks are self-contained entities: they always end in a
-- jump, either non-local or to another basic block in the same proc.
-- In this phase, we attempt to place the basic blocks in a sequence
-- such that as many of the local jumps as possible turn into
-- fallthroughs.

	:: NatCmmTop Instr
	-> NatCmmTop Instr

sequenceTop top@(CmmData _ _) = top
sequenceTop (CmmProc info lbl params (ListGraph blocks)) = 
  CmmProc info lbl params (ListGraph $ makeFarBranches $ sequenceBlocks blocks)

-- The algorithm is very simple (and stupid): we make a graph out of
-- the blocks where there is an edge from one block to another iff the
-- first block ends by jumping to the second.  Then we topologically
-- sort this graph.  Then traverse the list: for each block, we first
-- output the block, then if it has an out edge, we move the
-- destination of the out edge to the front of the list, and continue.

-- FYI, the classic layout for basic blocks uses postorder DFS; this
-- algorithm is implemented in cmm/ZipCfg.hs (NR 6 Sep 2007).

	:: Instruction instr
	=> [NatBasicBlock instr] 
	-> [NatBasicBlock instr]

sequenceBlocks [] = []
sequenceBlocks (entry:blocks) = 
  seqBlocks (mkNode entry : reverse (flattenSCCs (sccBlocks blocks)))
  -- the first block is the entry point ==> it must remain at the start.

	:: Instruction instr
	=> [NatBasicBlock instr] 
	-> [SCC ( NatBasicBlock instr
		, Unique
		, [Unique])]

sccBlocks blocks = stronglyConnCompFromEdgedVerticesR (map mkNode blocks)

-- we're only interested in the last instruction of
-- the block, and only if it has a single destination.
	:: Instruction instr
	=> [instr] -> [Unique]

getOutEdges instrs 
	= case jumpDestsOfInstr (last instrs) of
		[one] -> [getUnique one]
		_many -> []

mkNode block@(BasicBlock id instrs) = (block, getUnique id, getOutEdges instrs)

seqBlocks [] = []
seqBlocks ((block,_,[]) : rest)
  = block : seqBlocks rest
seqBlocks ((block@(BasicBlock id instrs),_,[next]) : rest)
  | can_fallthrough = BasicBlock id (init instrs) : seqBlocks rest'
  | otherwise       = block : seqBlocks rest'
	(can_fallthrough, rest') = reorder next [] rest
	  -- TODO: we should do a better job for cycles; try to maximise the
	  -- fallthroughs within a loop.
seqBlocks _ = panic "AsmCodegen:seqBlocks"

reorder id accum [] = (False, reverse accum)
reorder id accum (b@(block,id',out) : rest)
  | id == id'  = (True, (block,id,out) : reverse accum ++ rest)
  | otherwise  = reorder id (b:accum) rest

-- -----------------------------------------------------------------------------
-- Making far branches

-- Conditional branches on PowerPC are limited to +-32KB; if our Procs get too
-- big, we have to work around this limitation.

	:: [NatBasicBlock Instr] 
	-> [NatBasicBlock Instr]

#if powerpc_TARGET_ARCH
makeFarBranches blocks
    | last blockAddresses < nearLimit = blocks
    | otherwise = zipWith handleBlock blockAddresses blocks
        blockAddresses = scanl (+) 0 $ map blockLen blocks
        blockLen (BasicBlock _ instrs) = length instrs
        handleBlock addr (BasicBlock id instrs)
                = BasicBlock id (zipWith makeFar [addr..] instrs)
        makeFar addr (BCC ALWAYS tgt) = BCC ALWAYS tgt
        makeFar addr (BCC cond tgt)
            | abs (addr - targetAddr) >= nearLimit
            = BCCFAR cond tgt
            | otherwise
            = BCC cond tgt
            where Just targetAddr = lookupUFM blockAddressMap tgt
        makeFar addr other            = other
        nearLimit = 7000 -- 8192 instructions are allowed; let's keep some
                         -- distance, as we have a few pseudo-insns that are
                         -- pretty-printed as multiple instructions,
                         -- and it's just not worth the effort to calculate
                         -- things exactly
        blockAddressMap = listToUFM $ zip (map blockId blocks) blockAddresses
makeFarBranches = id

-- -----------------------------------------------------------------------------
-- Shortcut branches

	:: DynFlags 
	-> [NatCmmTop Instr] 
	-> [NatCmmTop Instr]

shortcutBranches dflags tops
  | optLevel dflags < 1 = tops    -- only with -O or higher
  | otherwise           = map (apply_mapping mapping) tops'
    (tops', mappings) = mapAndUnzip build_mapping tops
    mapping = foldr plusUFM emptyUFM mappings

build_mapping top@(CmmData _ _) = (top, emptyUFM)
build_mapping (CmmProc info lbl params (ListGraph []))
  = (CmmProc info lbl params (ListGraph []), emptyUFM)
build_mapping (CmmProc info lbl params (ListGraph (head:blocks)))
  = (CmmProc info lbl params (ListGraph (head:others)), mapping)
        -- drop the shorted blocks, but don't ever drop the first one,
        -- because it is pointed to by a global label.
    -- find all the blocks that just consist of a jump that can be
    -- shorted.
    (shortcut_blocks, others) = partitionWith split blocks
    split (BasicBlock id [insn]) | Just dest <- canShortcut insn 
                                 = Left (id,dest)
    split other = Right other

    -- build a mapping from BlockId to JumpDest for shorting branches
    mapping = foldl add emptyUFM shortcut_blocks
    add ufm (id,dest) = addToUFM ufm id dest
apply_mapping ufm (CmmData sec statics) 
  = CmmData sec (map (shortcutStatic (lookupUFM ufm)) statics)
  -- we need to get the jump tables, so apply the mapping to the entries
  -- of a CmmData too.
apply_mapping ufm (CmmProc info lbl params (ListGraph blocks))
  = CmmProc info lbl params (ListGraph $ map short_bb blocks)
    short_bb (BasicBlock id insns) = BasicBlock id $! map short_insn insns
    short_insn i = shortcutJump (lookupUFM ufm) i
                 -- shortcutJump should apply the mapping repeatedly,
                 -- just in case we can short multiple branches.

-- -----------------------------------------------------------------------------
-- Instruction selection

-- Native code instruction selection for a chunk of stix code.  For
-- this part of the computation, we switch from the UniqSM monad to
-- the NatM monad.  The latter carries not only a Unique, but also an
-- Int denoting the current C stack pointer offset in the generated
-- code; this is needed for creating correct spill offsets on
-- architectures which don't offer, or for which it would be
-- prohibitively expensive to employ, a frame pointer register.  Viz,
-- x86.

-- The offset is measured in bytes, and indicates the difference
-- between the current (simulated) C stack-ptr and the value it was at
-- the beginning of the block.  For stacks which grow down, this value
-- should be either zero or negative.

-- Switching between the two monads whilst carrying along the same
-- Unique supply breaks abstraction.  Is that bad?

	:: DynFlags 
	-> RawCmmTop 
	-> UniqSM 
		( [NatCmmTop Instr]
		, [CLabel])

genMachCode dflags cmm_top
  = do	{ initial_us <- getUs
	; let initial_st           = mkNatM_State initial_us 0 dflags
	      (new_tops, final_st) = initNat initial_st (cmmTopCodeGen dflags cmm_top)
	      final_delta          = natm_delta final_st
	      final_imports        = natm_imports final_st
	; if   final_delta == 0
          then return (new_tops, final_imports)
          else pprPanic "genMachCode: nonzero final delta" (int final_delta)

-- -----------------------------------------------------------------------------
-- Fixup assignments to global registers so that they assign to 
-- locations within the RegTable, if appropriate.

-- Note that we currently don't fixup reads here: they're done by
-- the generic optimiser below, to avoid having two separate passes
-- over the Cmm.

fixAssignsTop :: RawCmmTop -> UniqSM RawCmmTop
fixAssignsTop top@(CmmData _ _) = returnUs top
fixAssignsTop (CmmProc info lbl params (ListGraph blocks)) =
  mapUs fixAssignsBlock blocks `thenUs` \ blocks' ->
  returnUs (CmmProc info lbl params (ListGraph blocks'))

fixAssignsBlock :: CmmBasicBlock -> UniqSM CmmBasicBlock
fixAssignsBlock (BasicBlock id stmts) =
  fixAssigns stmts `thenUs` \ stmts' ->
  returnUs (BasicBlock id stmts')

fixAssigns :: [CmmStmt] -> UniqSM [CmmStmt]
fixAssigns stmts =
  mapUs fixAssign stmts `thenUs` \ stmtss ->
  returnUs (concat stmtss)

fixAssign :: CmmStmt -> UniqSM [CmmStmt]
fixAssign (CmmAssign (CmmGlobal reg) src)
  | Left  realreg <- reg_or_addr
  = returnUs [CmmAssign (CmmGlobal reg) src]
  | Right baseRegAddr <- reg_or_addr
  = returnUs [CmmStore baseRegAddr src]
           -- Replace register leaves with appropriate StixTrees for
           -- the given target. GlobalRegs which map to a reg on this
           -- arch are left unchanged.  Assigning to BaseReg is always
           -- illegal, so we check for that.
	reg_or_addr = get_GlobalReg_reg_or_addr reg

fixAssign other_stmt = returnUs [other_stmt]

-- -----------------------------------------------------------------------------
-- Generic Cmm optimiser

Here we do:

  (a) Constant folding
  (b) Simple inlining: a temporary which is assigned to and then
      used, once, can be shorted.
  (c) Replacement of references to GlobalRegs which do not have
      machine registers by the appropriate memory load (eg.
      Hp ==>  *(BaseReg + 34) ).
  (d) Position independent code and dynamic linking
        (i)  introduce the appropriate indirections
             and position independent refs
        (ii) compile a list of imported symbols

Ideas for other things we could do (ToDo):

  - shortcut jumps-to-jumps
  - eliminate dead code blocks
  - simple CSE: if an expr is assigned to a temp, then replace later occs of
    that expr with the temp, until the expr is no longer valid (can push through
    temp assignments, and certain assigns to mem...)

cmmToCmm :: DynFlags -> RawCmmTop -> (RawCmmTop, [CLabel])
cmmToCmm _ top@(CmmData _ _) = (top, [])
cmmToCmm dflags (CmmProc info lbl params (ListGraph blocks)) = runCmmOpt dflags $ do
  blocks' <- mapM cmmBlockConFold (cmmMiniInline blocks)
  return $ CmmProc info lbl params (ListGraph blocks')

newtype CmmOptM a = CmmOptM (([CLabel], DynFlags) -> (# a, [CLabel] #))

instance Monad CmmOptM where
  return x = CmmOptM $ \(imports, _) -> (# x,imports #)
  (CmmOptM f) >>= g =
    CmmOptM $ \(imports, dflags) ->
                case f (imports, dflags) of
                  (# x, imports' #) ->
                    case g x of
                      CmmOptM g' -> g' (imports', dflags)

addImportCmmOpt :: CLabel -> CmmOptM ()
addImportCmmOpt lbl = CmmOptM $ \(imports, dflags) -> (# (), lbl:imports #)

getDynFlagsCmmOpt :: CmmOptM DynFlags
getDynFlagsCmmOpt = CmmOptM $ \(imports, dflags) -> (# dflags, imports #)

runCmmOpt :: DynFlags -> CmmOptM a -> (a, [CLabel])
runCmmOpt dflags (CmmOptM f) = case f ([], dflags) of
                        (# result, imports #) -> (result, imports)

cmmBlockConFold :: CmmBasicBlock -> CmmOptM CmmBasicBlock
cmmBlockConFold (BasicBlock id stmts) = do
  stmts' <- mapM cmmStmtConFold stmts
  return $ BasicBlock id stmts'

cmmStmtConFold stmt
   = case stmt of
        CmmAssign reg src
           -> do src' <- cmmExprConFold DataReference src
                 return $ case src' of
		   CmmReg reg' | reg == reg' -> CmmNop
		   new_src -> CmmAssign reg new_src

        CmmStore addr src
           -> do addr' <- cmmExprConFold DataReference addr
                 src'  <- cmmExprConFold DataReference src
                 return $ CmmStore addr' src'

        CmmJump addr regs
           -> do addr' <- cmmExprConFold JumpReference addr
                 return $ CmmJump addr' regs

	CmmCall target regs args srt returns
	   -> do target' <- case target of
			      CmmCallee e conv -> do
			        e' <- cmmExprConFold CallReference e
			        return $ CmmCallee e' conv
			      other -> return other
                 args' <- mapM (\(CmmHinted arg hint) -> do
                                  arg' <- cmmExprConFold DataReference arg
                                  return (CmmHinted arg' hint)) args
	         return $ CmmCall target' regs args' srt returns

        CmmCondBranch test dest
           -> do test' <- cmmExprConFold DataReference test
	         return $ case test' of
		   CmmLit (CmmInt 0 _) -> 
		     CmmComment (mkFastString ("deleted: " ++ 
					showSDoc (pprStmt stmt)))

		   CmmLit (CmmInt n _) -> CmmBranch dest
		   other -> CmmCondBranch test' dest

	CmmSwitch expr ids
	   -> do expr' <- cmmExprConFold DataReference expr
	         return $ CmmSwitch expr' ids

           -> return other

cmmExprConFold referenceKind expr
   = case expr of
        CmmLoad addr rep
           -> do addr' <- cmmExprConFold DataReference addr
                 return $ CmmLoad addr' rep

        CmmMachOp mop args
           -- For MachOps, we first optimize the children, and then we try 
           -- our hand at some constant-folding.
           -> do args' <- mapM (cmmExprConFold DataReference) args
                 return $ cmmMachOpFold mop args'

        CmmLit (CmmLabel lbl)
           -> do
		dflags <- getDynFlagsCmmOpt
		cmmMakeDynamicReference dflags addImportCmmOpt referenceKind lbl
        CmmLit (CmmLabelOff lbl off)
           -> do
		 dflags <- getDynFlagsCmmOpt
		 dynRef <- cmmMakeDynamicReference dflags addImportCmmOpt referenceKind lbl
                 return $ cmmMachOpFold (MO_Add wordWidth) [
                     (CmmLit $ CmmInt (fromIntegral off) wordWidth)

#if powerpc_TARGET_ARCH
           -- On powerpc (non-PIC), it's easier to jump directly to a label than
           -- to use the register table, so we replace these registers
           -- with the corresponding labels:
        CmmReg (CmmGlobal EagerBlackholeInfo)
          | not opt_PIC
          -> cmmExprConFold referenceKind $
             CmmLit (CmmLabel (mkRtsCodeLabel (sLit "__stg_EAGER_BLACKHOLE_INFO"))) 
        CmmReg (CmmGlobal GCEnter1)
          | not opt_PIC
          -> cmmExprConFold referenceKind $
             CmmLit (CmmLabel (mkRtsCodeLabel (sLit "__stg_gc_enter_1"))) 
        CmmReg (CmmGlobal GCFun)
          | not opt_PIC
          -> cmmExprConFold referenceKind $
             CmmLit (CmmLabel (mkRtsCodeLabel (sLit "__stg_gc_fun")))

        CmmReg (CmmGlobal mid)
           -- Replace register leaves with appropriate StixTrees for
           -- the given target.  MagicIds which map to a reg on this
           -- arch are left unchanged.  For the rest, BaseReg is taken
           -- to mean the address of the reg table in MainCapability,
           -- and for all others we generate an indirection to its
           -- location in the register table.
           -> case get_GlobalReg_reg_or_addr mid of
                 Left  realreg -> return expr
                 Right baseRegAddr 
                    -> case mid of 
                          BaseReg -> cmmExprConFold DataReference baseRegAddr
                          other   -> cmmExprConFold DataReference
                                        (CmmLoad baseRegAddr (globalRegType mid))
	   -- eliminate zero offsets
	CmmRegOff reg 0
	   -> cmmExprConFold referenceKind (CmmReg reg)

        CmmRegOff (CmmGlobal mid) offset
           -- RegOf leaves are just a shorthand form. If the reg maps
           -- to a real reg, we keep the shorthand, otherwise, we just
           -- expand it and defer to the above code. 
           -> case get_GlobalReg_reg_or_addr mid of
                Left  realreg -> return expr
                Right baseRegAddr
                   -> cmmExprConFold DataReference (CmmMachOp (MO_Add wordWidth) [
                                        CmmReg (CmmGlobal mid),
                                        CmmLit (CmmInt (fromIntegral offset)
           -> return other

-- -----------------------------------------------------------------------------
-- Utils

bind f x = x $! f