-----------------------------------------------------------------------------
--
-- (c) The University of Glasgow 2011
--
-- CmmLint: checking the correctness of Cmm statements and expressions
--
-----------------------------------------------------------------------------
{-# LANGUAGE GADTs #-}
module CmmLint (
    cmmLint, cmmLintGraph
  ) where

import GhcPrelude

import Hoopl.Block
import Hoopl.Collections
import Hoopl.Graph
import Hoopl.Label
import Cmm
import CmmUtils
import CmmLive
import CmmSwitch (switchTargetsToList)
import PprCmm ()
import Outputable
import DynFlags

import Control.Monad (liftM, ap)

-- Things to check:
--     - invariant on CmmBlock in CmmExpr (see comment there)
--     - check for branches to blocks that don't exist
--     - check types

-- -----------------------------------------------------------------------------
-- Exported entry points:

cmmLint :: (Outputable d, Outputable h)
        => DynFlags -> GenCmmGroup d h CmmGraph -> Maybe SDoc
cmmLint dflags tops = runCmmLint dflags (mapM_ (lintCmmDecl dflags)) tops

cmmLintGraph :: DynFlags -> CmmGraph -> Maybe SDoc
cmmLintGraph dflags g = runCmmLint dflags (lintCmmGraph dflags) g

runCmmLint :: Outputable a => DynFlags -> (a -> CmmLint b) -> a -> Maybe SDoc
runCmmLint dflags l p =
   case unCL (l p) dflags of
     Left err -> Just (vcat [text "Cmm lint error:",
                             nest 2 err,
                             text "Program was:",
                             nest 2 (ppr p)])
     Right _  -> Nothing

lintCmmDecl :: DynFlags -> GenCmmDecl h i CmmGraph -> CmmLint ()
lintCmmDecl dflags (CmmProc _ lbl _ g)
  = addLintInfo (text "in proc " <> ppr lbl) $ lintCmmGraph dflags g
lintCmmDecl _ (CmmData {})
  = return ()


lintCmmGraph :: DynFlags -> CmmGraph -> CmmLint ()
lintCmmGraph dflags g =
    cmmLocalLiveness dflags g `seq` mapM_ (lintCmmBlock labels) blocks
    -- cmmLiveness throws an error if there are registers
    -- live on entry to the graph (i.e. undefined
    -- variables)
  where
       blocks = toBlockList g
       labels = setFromList (map entryLabel blocks)


lintCmmBlock :: LabelSet -> CmmBlock -> CmmLint ()
lintCmmBlock labels block
  = addLintInfo (text "in basic block " <> ppr (entryLabel block)) $ do
        let (_, middle, last) = blockSplit block
        mapM_ lintCmmMiddle (blockToList middle)
        lintCmmLast labels last

-- -----------------------------------------------------------------------------
-- lintCmmExpr

-- Checks whether a CmmExpr is "type-correct", and check for obvious-looking
-- byte/word mismatches.

lintCmmExpr :: CmmExpr -> CmmLint CmmType
lintCmmExpr (CmmLoad expr rep) = do
  _ <- lintCmmExpr expr
  -- Disabled, if we have the inlining phase before the lint phase,
  -- we can have funny offsets due to pointer tagging. -- EZY
  -- when (widthInBytes (typeWidth rep) >= wORD_SIZE) $
  --   cmmCheckWordAddress expr
  return rep
lintCmmExpr expr@(CmmMachOp op args) = do
  dflags <- getDynFlags
  tys <- mapM lintCmmExpr args
  if map (typeWidth . cmmExprType dflags) args == machOpArgReps dflags op
        then cmmCheckMachOp op args tys
        else cmmLintMachOpErr expr (map (cmmExprType dflags) args) (machOpArgReps dflags op)
lintCmmExpr (CmmRegOff reg offset)
  = do dflags <- getDynFlags
       let rep = typeWidth (cmmRegType dflags reg)
       lintCmmExpr (CmmMachOp (MO_Add rep)
                [CmmReg reg, CmmLit (CmmInt (fromIntegral offset) rep)])
lintCmmExpr expr =
  do dflags <- getDynFlags
     return (cmmExprType dflags expr)

-- Check for some common byte/word mismatches (eg. Sp + 1)
cmmCheckMachOp   :: MachOp -> [CmmExpr] -> [CmmType] -> CmmLint CmmType
cmmCheckMachOp op [lit@(CmmLit (CmmInt { })), reg@(CmmReg _)] tys
  = cmmCheckMachOp op [reg, lit] tys
cmmCheckMachOp op _ tys
  = do dflags <- getDynFlags
       return (machOpResultType dflags op tys)

{-
isOffsetOp :: MachOp -> Bool
isOffsetOp (MO_Add _) = True
isOffsetOp (MO_Sub _) = True
isOffsetOp _ = False

-- This expression should be an address from which a word can be loaded:
-- check for funny-looking sub-word offsets.
_cmmCheckWordAddress :: CmmExpr -> CmmLint ()
_cmmCheckWordAddress e@(CmmMachOp op [arg, CmmLit (CmmInt i _)])
  | isOffsetOp op && notNodeReg arg && i `rem` fromIntegral (wORD_SIZE dflags) /= 0
  = cmmLintDubiousWordOffset e
_cmmCheckWordAddress e@(CmmMachOp op [CmmLit (CmmInt i _), arg])
  | isOffsetOp op && notNodeReg arg && i `rem` fromIntegral (wORD_SIZE dflags) /= 0
  = cmmLintDubiousWordOffset e
_cmmCheckWordAddress _
  = return ()

-- No warnings for unaligned arithmetic with the node register,
-- which is used to extract fields from tagged constructor closures.
notNodeReg :: CmmExpr -> Bool
notNodeReg (CmmReg reg) | reg == nodeReg = False
notNodeReg _                             = True
-}

lintCmmMiddle :: CmmNode O O -> CmmLint ()
lintCmmMiddle node = case node of
  CmmComment _ -> return ()
  CmmTick _    -> return ()
  CmmUnwind{}  -> return ()

  CmmAssign reg expr -> do
            dflags <- getDynFlags
            erep <- lintCmmExpr expr
            let reg_ty = cmmRegType dflags reg
            if (erep `cmmEqType_ignoring_ptrhood` reg_ty)
                then return ()
                else cmmLintAssignErr (CmmAssign reg expr) erep reg_ty

  CmmStore l r -> do
            _ <- lintCmmExpr l
            _ <- lintCmmExpr r
            return ()

  CmmUnsafeForeignCall target _formals actuals -> do
            lintTarget target
            mapM_ lintCmmExpr actuals


lintCmmLast :: LabelSet -> CmmNode O C -> CmmLint ()
lintCmmLast labels node = case node of
  CmmBranch id -> checkTarget id

  CmmCondBranch e t f _ -> do
            dflags <- getDynFlags
            mapM_ checkTarget [t,f]
            _ <- lintCmmExpr e
            checkCond dflags e

  CmmSwitch e ids -> do
            dflags <- getDynFlags
            mapM_ checkTarget $ switchTargetsToList ids
            erep <- lintCmmExpr e
            if (erep `cmmEqType_ignoring_ptrhood` bWord dflags)
              then return ()
              else cmmLintErr (text "switch scrutinee is not a word: " <>
                               ppr e <> text " :: " <> ppr erep)

  CmmCall { cml_target = target, cml_cont = cont } -> do
          _ <- lintCmmExpr target
          maybe (return ()) checkTarget cont

  CmmForeignCall tgt _ args succ _ _ _ -> do
          lintTarget tgt
          mapM_ lintCmmExpr args
          checkTarget succ
 where
  checkTarget id
     | setMember id labels = return ()
     | otherwise = cmmLintErr (text "Branch to nonexistent id" <+> ppr id)


lintTarget :: ForeignTarget -> CmmLint ()
lintTarget (ForeignTarget e _) = lintCmmExpr e >> return ()
lintTarget (PrimTarget {})     = return ()


checkCond :: DynFlags -> CmmExpr -> CmmLint ()
checkCond _ (CmmMachOp mop _) | isComparisonMachOp mop = return ()
checkCond dflags (CmmLit (CmmInt x t)) | x == 0 || x == 1, t == wordWidth dflags = return () -- constant values
checkCond _ expr
    = cmmLintErr (hang (text "expression is not a conditional:") 2
                         (ppr expr))

-- -----------------------------------------------------------------------------
-- CmmLint monad

-- just a basic error monad:

newtype CmmLint a = CmmLint { unCL :: DynFlags -> Either SDoc a }

instance Functor CmmLint where
      fmap = liftM

instance Applicative CmmLint where
      pure a = CmmLint (\_ -> Right a)
      (<*>) = ap

instance Monad CmmLint where
  CmmLint m >>= k = CmmLint $ \dflags ->
                                case m dflags of
                                Left e -> Left e
                                Right a -> unCL (k a) dflags

instance HasDynFlags CmmLint where
    getDynFlags = CmmLint (\dflags -> Right dflags)

cmmLintErr :: SDoc -> CmmLint a
cmmLintErr msg = CmmLint (\_ -> Left msg)

addLintInfo :: SDoc -> CmmLint a -> CmmLint a
addLintInfo info thing = CmmLint $ \dflags ->
   case unCL thing dflags of
        Left err -> Left (hang info 2 err)
        Right a  -> Right a

cmmLintMachOpErr :: CmmExpr -> [CmmType] -> [Width] -> CmmLint a
cmmLintMachOpErr expr argsRep opExpectsRep
     = cmmLintErr (text "in MachOp application: " $$
                   nest 2 (ppr  expr) $$
                      (text "op is expecting: " <+> ppr opExpectsRep) $$
                      (text "arguments provide: " <+> ppr argsRep))

cmmLintAssignErr :: CmmNode e x -> CmmType -> CmmType -> CmmLint a
cmmLintAssignErr stmt e_ty r_ty
  = cmmLintErr (text "in assignment: " $$
                nest 2 (vcat [ppr stmt,
                              text "Reg ty:" <+> ppr r_ty,
                              text "Rhs ty:" <+> ppr e_ty]))


{-
cmmLintDubiousWordOffset :: CmmExpr -> CmmLint a
cmmLintDubiousWordOffset expr
   = cmmLintErr (text "offset is not a multiple of words: " $$
                 nest 2 (ppr expr))
-}

