{-# LANGUAGE RankNTypes #-}
{-# OPTIONS -optc-DNON_POSIX_SOURCE #-}

module PrelRules ( primOpRules, builtinRules ) where

#include "HsVersions.h"
#include "../includes/MachDeps.h"

import {-# SOURCE #-} MkId ( mkPrimOpId, magicDictId )

import CoreSyn
import MkCore
import Id
import Literal
import CoreSubst   ( exprIsLiteral_maybe )
import PrimOp      ( PrimOp(..), tagToEnumKey )
import TysWiredIn
import TysPrim
import TyCon       ( tyConDataCons_maybe, isEnumerationTyCon, isNewTyCon, unwrapNewTyCon_maybe )
import DataCon     ( dataConTag, dataConTyCon, dataConWorkId )
import CoreUtils   ( cheapEqExpr, exprIsHNF )
import CoreUnfold  ( exprIsConApp_maybe )
import Type
import TypeRep
import OccName     ( occNameFS )
import PrelNames
import Maybes      ( orElse )
import Name        ( Name, nameOccName )
import Outputable
import FastString
import BasicTypes
import DynFlags
import Platform
import Util
import Coercion     (mkUnbranchedAxInstCo,mkSymCo,Role(..))

import Control.Applicative ( Applicative(..), Alternative(..) )
import Control.Monad
import Data.Bits as Bits
import qualified Data.ByteString as BS
import Data.Int
import Data.Ratio
import Data.Word

primOpRules :: Name -> PrimOp -> Maybe CoreRule
    -- ToDo: something for integer-shift ops?
    --       NotOp
primOpRules nm TagToEnumOp = mkPrimOpRule nm 2 [ tagToEnumRule ]
primOpRules nm DataToTagOp = mkPrimOpRule nm 2 [ dataToTagRule ]

-- Int operations
primOpRules nm IntAddOp    = mkPrimOpRule nm 2 [ binaryLit (intOp2 (+))
                                               , identityDynFlags zeroi ]
primOpRules nm IntSubOp    = mkPrimOpRule nm 2 [ binaryLit (intOp2 (-))
                                               , rightIdentityDynFlags zeroi
                                               , equalArgs >> retLit zeroi ]
primOpRules nm IntMulOp    = mkPrimOpRule nm 2 [ binaryLit (intOp2 (*))
                                               , zeroElem zeroi
                                               , identityDynFlags onei ]
primOpRules nm IntQuotOp   = mkPrimOpRule nm 2 [ nonZeroLit 1 >> binaryLit (intOp2 quot)
                                               , leftZero zeroi
                                               , rightIdentityDynFlags onei
                                               , equalArgs >> retLit onei ]
primOpRules nm IntRemOp    = mkPrimOpRule nm 2 [ nonZeroLit 1 >> binaryLit (intOp2 rem)
                                               , leftZero zeroi
                                               , do l <- getLiteral 1
                                                    dflags <- getDynFlags
                                                    guard (l == onei dflags)
                                                    retLit zeroi
                                               , equalArgs >> retLit zeroi
                                               , equalArgs >> retLit zeroi ]
primOpRules nm AndIOp      = mkPrimOpRule nm 2 [ binaryLit (intOp2 (.&.))
                                               , idempotent
                                               , zeroElem zeroi ]
primOpRules nm OrIOp       = mkPrimOpRule nm 2 [ binaryLit (intOp2 (.|.))
                                               , idempotent
                                               , identityDynFlags zeroi ]
primOpRules nm XorIOp      = mkPrimOpRule nm 2 [ binaryLit (intOp2 xor)
                                               , identityDynFlags zeroi
                                               , equalArgs >> retLit zeroi ]
primOpRules nm IntNegOp    = mkPrimOpRule nm 1 [ unaryLit negOp
                                               , inversePrimOp IntNegOp ]
primOpRules nm ISllOp      = mkPrimOpRule nm 2 [ binaryLit (intOp2 Bits.shiftL)
                                               , rightIdentityDynFlags zeroi ]
primOpRules nm ISraOp      = mkPrimOpRule nm 2 [ binaryLit (intOp2 Bits.shiftR)
                                               , rightIdentityDynFlags zeroi ]
primOpRules nm ISrlOp      = mkPrimOpRule nm 2 [ binaryLit (intOp2 shiftRightLogical)
                                               , rightIdentityDynFlags zeroi ]

-- Word operations
primOpRules nm WordAddOp   = mkPrimOpRule nm 2 [ binaryLit (wordOp2 (+))
                                               , identityDynFlags zerow ]
primOpRules nm WordSubOp   = mkPrimOpRule nm 2 [ binaryLit (wordOp2 (-))
                                               , rightIdentityDynFlags zerow
                                               , equalArgs >> retLit zerow ]
primOpRules nm WordMulOp   = mkPrimOpRule nm 2 [ binaryLit (wordOp2 (*))
                                               , identityDynFlags onew ]
primOpRules nm WordQuotOp  = mkPrimOpRule nm 2 [ nonZeroLit 1 >> binaryLit (wordOp2 quot)
                                               , rightIdentityDynFlags onew ]
primOpRules nm WordRemOp   = mkPrimOpRule nm 2 [ nonZeroLit 1 >> binaryLit (wordOp2 rem)
                                               , rightIdentityDynFlags onew ]
primOpRules nm AndOp       = mkPrimOpRule nm 2 [ binaryLit (wordOp2 (.&.))
                                               , idempotent
                                               , zeroElem zerow ]
primOpRules nm OrOp        = mkPrimOpRule nm 2 [ binaryLit (wordOp2 (.|.))
                                               , idempotent
                                               , identityDynFlags zerow ]
primOpRules nm XorOp       = mkPrimOpRule nm 2 [ binaryLit (wordOp2 xor)
                                               , identityDynFlags zerow
                                               , equalArgs >> retLit zerow ]
primOpRules nm SllOp       = mkPrimOpRule nm 2 [ wordShiftRule Bits.shiftL ]
primOpRules nm SrlOp       = mkPrimOpRule nm 2 [ wordShiftRule shiftRightLogical ]

-- coercions
primOpRules nm Word2IntOp     = mkPrimOpRule nm 1 [ liftLitDynFlags word2IntLit
                                                  , inversePrimOp Int2WordOp ]
primOpRules nm Int2WordOp     = mkPrimOpRule nm 1 [ liftLitDynFlags int2WordLit
                                                  , inversePrimOp Word2IntOp ]
primOpRules nm Narrow8IntOp   = mkPrimOpRule nm 1 [ liftLit narrow8IntLit
                                                  , subsumedByPrimOp Narrow8IntOp
                                                  , Narrow8IntOp `subsumesPrimOp` Narrow16IntOp
                                                  , Narrow8IntOp `subsumesPrimOp` Narrow32IntOp ]
primOpRules nm Narrow16IntOp  = mkPrimOpRule nm 1 [ liftLit narrow16IntLit
                                                  , subsumedByPrimOp Narrow8IntOp
                                                  , subsumedByPrimOp Narrow16IntOp
                                                  , Narrow16IntOp `subsumesPrimOp` Narrow32IntOp ]
primOpRules nm Narrow32IntOp  = mkPrimOpRule nm 1 [ liftLit narrow32IntLit
                                                  , subsumedByPrimOp Narrow8IntOp
                                                  , subsumedByPrimOp Narrow16IntOp
                                                  , subsumedByPrimOp Narrow32IntOp
                                                  , removeOp32 ]
primOpRules nm Narrow8WordOp  = mkPrimOpRule nm 1 [ liftLit narrow8WordLit
                                                  , subsumedByPrimOp Narrow8WordOp
                                                  , Narrow8WordOp `subsumesPrimOp` Narrow16WordOp
                                                  , Narrow8WordOp `subsumesPrimOp` Narrow32WordOp ]
primOpRules nm Narrow16WordOp = mkPrimOpRule nm 1 [ liftLit narrow16WordLit
                                                  , subsumedByPrimOp Narrow8WordOp
                                                  , subsumedByPrimOp Narrow16WordOp
                                                  , Narrow16WordOp `subsumesPrimOp` Narrow32WordOp ]
primOpRules nm Narrow32WordOp = mkPrimOpRule nm 1 [ liftLit narrow32WordLit
                                                  , subsumedByPrimOp Narrow8WordOp
                                                  , subsumedByPrimOp Narrow16WordOp
                                                  , subsumedByPrimOp Narrow32WordOp
                                                  , removeOp32 ]
primOpRules nm OrdOp          = mkPrimOpRule nm 1 [ liftLit char2IntLit
                                                  , inversePrimOp ChrOp ]
primOpRules nm ChrOp          = mkPrimOpRule nm 1 [ do [Lit lit] <- getArgs
                                                       guard (litFitsInChar lit)
                                                       liftLit int2CharLit
                                                  , inversePrimOp OrdOp ]
primOpRules nm Float2IntOp    = mkPrimOpRule nm 1 [ liftLit float2IntLit ]
primOpRules nm Int2FloatOp    = mkPrimOpRule nm 1 [ liftLit int2FloatLit ]
primOpRules nm Double2IntOp   = mkPrimOpRule nm 1 [ liftLit double2IntLit ]
primOpRules nm Int2DoubleOp   = mkPrimOpRule nm 1 [ liftLit int2DoubleLit ]
-- SUP: Not sure what the standard says about precision in the following 2 cases
primOpRules nm Float2DoubleOp = mkPrimOpRule nm 1 [ liftLit float2DoubleLit ]
primOpRules nm Double2FloatOp = mkPrimOpRule nm 1 [ liftLit double2FloatLit ]

-- Float
primOpRules nm FloatAddOp   = mkPrimOpRule nm 2 [ binaryLit (floatOp2 (+))
                                                , identity zerof ]
primOpRules nm FloatSubOp   = mkPrimOpRule nm 2 [ binaryLit (floatOp2 (-))
                                                , rightIdentity zerof ]
primOpRules nm FloatMulOp   = mkPrimOpRule nm 2 [ binaryLit (floatOp2 (*))
                                                , identity onef
                                                , strengthReduction twof FloatAddOp  ]
                         -- zeroElem zerof doesn't hold because of NaN
primOpRules nm FloatDivOp   = mkPrimOpRule nm 2 [ guardFloatDiv >> binaryLit (floatOp2 (/))
                                                , rightIdentity onef ]
primOpRules nm FloatNegOp   = mkPrimOpRule nm 1 [ unaryLit negOp
                                                , inversePrimOp FloatNegOp ]

-- Double
primOpRules nm DoubleAddOp   = mkPrimOpRule nm 2 [ binaryLit (doubleOp2 (+))
                                                 , identity zerod ]
primOpRules nm DoubleSubOp   = mkPrimOpRule nm 2 [ binaryLit (doubleOp2 (-))
                                                 , rightIdentity zerod ]
primOpRules nm DoubleMulOp   = mkPrimOpRule nm 2 [ binaryLit (doubleOp2 (*))
                                                 , identity oned
                                                 , strengthReduction twod DoubleAddOp  ]
                          -- zeroElem zerod doesn't hold because of NaN
primOpRules nm DoubleDivOp   = mkPrimOpRule nm 2 [ guardDoubleDiv >> binaryLit (doubleOp2 (/))
                                                 , rightIdentity oned ]
primOpRules nm DoubleNegOp   = mkPrimOpRule nm 1 [ unaryLit negOp
                                                 , inversePrimOp DoubleNegOp ]

-- Relational operators

primOpRules nm IntEqOp    = mkRelOpRule nm (==) [ litEq True ]
primOpRules nm IntNeOp    = mkRelOpRule nm (/=) [ litEq False ]
primOpRules nm CharEqOp   = mkRelOpRule nm (==) [ litEq True ]
primOpRules nm CharNeOp   = mkRelOpRule nm (/=) [ litEq False ]

primOpRules nm IntGtOp    = mkRelOpRule nm (>)  [ boundsCmp Gt ]
primOpRules nm IntGeOp    = mkRelOpRule nm (>=) [ boundsCmp Ge ]
primOpRules nm IntLeOp    = mkRelOpRule nm (<=) [ boundsCmp Le ]
primOpRules nm IntLtOp    = mkRelOpRule nm (<)  [ boundsCmp Lt ]

primOpRules nm CharGtOp   = mkRelOpRule nm (>)  [ boundsCmp Gt ]
primOpRules nm CharGeOp   = mkRelOpRule nm (>=) [ boundsCmp Ge ]
primOpRules nm CharLeOp   = mkRelOpRule nm (<=) [ boundsCmp Le ]
primOpRules nm CharLtOp   = mkRelOpRule nm (<)  [ boundsCmp Lt ]

primOpRules nm FloatGtOp  = mkFloatingRelOpRule nm (>)  []
primOpRules nm FloatGeOp  = mkFloatingRelOpRule nm (>=) []
primOpRules nm FloatLeOp  = mkFloatingRelOpRule nm (<=) []
primOpRules nm FloatLtOp  = mkFloatingRelOpRule nm (<)  []
primOpRules nm FloatEqOp  = mkFloatingRelOpRule nm (==) [ litEq True ]
primOpRules nm FloatNeOp  = mkFloatingRelOpRule nm (/=) [ litEq False ]

primOpRules nm DoubleGtOp = mkFloatingRelOpRule nm (>)  []
primOpRules nm DoubleGeOp = mkFloatingRelOpRule nm (>=) []
primOpRules nm DoubleLeOp = mkFloatingRelOpRule nm (<=) []
primOpRules nm DoubleLtOp = mkFloatingRelOpRule nm (<)  []
primOpRules nm DoubleEqOp = mkFloatingRelOpRule nm (==) [ litEq True ]
primOpRules nm DoubleNeOp = mkFloatingRelOpRule nm (/=) [ litEq False ]

primOpRules nm WordGtOp   = mkRelOpRule nm (>)  [ boundsCmp Gt ]
primOpRules nm WordGeOp   = mkRelOpRule nm (>=) [ boundsCmp Ge ]
primOpRules nm WordLeOp   = mkRelOpRule nm (<=) [ boundsCmp Le ]
primOpRules nm WordLtOp   = mkRelOpRule nm (<)  [ boundsCmp Lt ]
primOpRules nm WordEqOp   = mkRelOpRule nm (==) [ litEq True ]
primOpRules nm WordNeOp   = mkRelOpRule nm (/=) [ litEq False ]

primOpRules nm AddrAddOp  = mkPrimOpRule nm 2 [ rightIdentityDynFlags zeroi ]

primOpRules nm SeqOp      = mkPrimOpRule nm 4 [ seqRule ]
primOpRules nm SparkOp    = mkPrimOpRule nm 4 [ sparkRule ]

primOpRules _  _          = Nothing

-- useful shorthands
mkPrimOpRule :: Name -> Int -> [RuleM CoreExpr] -> Maybe CoreRule
mkPrimOpRule nm arity rules = Just $ mkBasicRule nm arity (msum rules)

mkRelOpRule :: Name -> (forall a . Ord a => a -> a -> Bool)
            -> [RuleM CoreExpr] -> Maybe CoreRule
mkRelOpRule nm cmp extra
  = mkPrimOpRule nm 2 $ rules ++ extra
  where
    rules = [ binaryCmpLit cmp
            , do equalArgs
              -- x `cmp` x does not depend on x, so
              -- compute it for the arbitrary value 'True'
              -- and use that result
                 dflags <- getDynFlags
                 return (if cmp True True
                         then trueValInt  dflags
                         else falseValInt dflags) ]

-- Note [Rules for floating-point comparisons]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- We need different rules for floating-point values because for floats
-- it is not true that x = x. The special case when this does not occur
-- are NaNs.

mkFloatingRelOpRule :: Name -> (forall a . Ord a => a -> a -> Bool)
                    -> [RuleM CoreExpr] -> Maybe CoreRule
mkFloatingRelOpRule nm cmp extra -- See Note [Rules for floating-point comparisons]
  = mkPrimOpRule nm 2 $ binaryCmpLit cmp : extra

-- common constants
zeroi, onei, zerow, onew :: DynFlags -> Literal
zeroi dflags = mkMachInt  dflags 0
onei  dflags = mkMachInt  dflags 1
zerow dflags = mkMachWord dflags 0
onew  dflags = mkMachWord dflags 1

zerof, onef, twof, zerod, oned, twod :: Literal
zerof = mkMachFloat 0.0
onef  = mkMachFloat 1.0
twof  = mkMachFloat 2.0
zerod = mkMachDouble 0.0
oned  = mkMachDouble 1.0
twod  = mkMachDouble 2.0

cmpOp :: DynFlags -> (forall a . Ord a => a -> a -> Bool)
      -> Literal -> Literal -> Maybe CoreExpr
cmpOp dflags cmp = go
  where
    done True  = Just $ trueValInt  dflags
    done False = Just $ falseValInt dflags

    -- These compares are at different types
    go (MachChar i1)   (MachChar i2)   = done (i1 `cmp` i2)
    go (MachInt i1)    (MachInt i2)    = done (i1 `cmp` i2)
    go (MachInt64 i1)  (MachInt64 i2)  = done (i1 `cmp` i2)
    go (MachWord i1)   (MachWord i2)   = done (i1 `cmp` i2)
    go (MachWord64 i1) (MachWord64 i2) = done (i1 `cmp` i2)
    go (MachFloat i1)  (MachFloat i2)  = done (i1 `cmp` i2)
    go (MachDouble i1) (MachDouble i2) = done (i1 `cmp` i2)
    go _               _               = Nothing

--------------------------

negOp :: DynFlags -> Literal -> Maybe CoreExpr  -- Negate
negOp _      (MachFloat 0.0)  = Nothing  -- can't represent -0.0 as a Rational
negOp dflags (MachFloat f)    = Just (mkFloatVal dflags (-f))
negOp _      (MachDouble 0.0) = Nothing
negOp dflags (MachDouble d)   = Just (mkDoubleVal dflags (-d))
negOp dflags (MachInt i)      = intResult dflags (-i)
negOp _      _                = Nothing

--------------------------
intOp2 :: (Integral a, Integral b)
       => (a -> b -> Integer)
       -> DynFlags -> Literal -> Literal -> Maybe CoreExpr
intOp2 op dflags (MachInt i1) (MachInt i2) = intResult dflags (fromInteger i1 `op` fromInteger i2)
intOp2 _  _      _            _            = Nothing  -- Could find LitLit

shiftRightLogical :: Integer -> Int -> Integer
-- Shift right, putting zeros in rather than sign-propagating as Bits.shiftR would do
-- Do this by converting to Word and back.  Obviously this won't work for big
-- values, but its ok as we use it here
shiftRightLogical x n = fromIntegral (fromInteger x `shiftR` n :: Word)


--------------------------
retLit :: (DynFlags -> Literal) -> RuleM CoreExpr
retLit l = do dflags <- getDynFlags
              return $ Lit $ l dflags

wordOp2 :: (Integral a, Integral b)
        => (a -> b -> Integer)
        -> DynFlags -> Literal -> Literal -> Maybe CoreExpr
wordOp2 op dflags (MachWord w1) (MachWord w2)
    = wordResult dflags (fromInteger w1 `op` fromInteger w2)
wordOp2 _ _ _ _ = Nothing  -- Could find LitLit

wordShiftRule :: (Integer -> Int -> Integer) -> RuleM CoreExpr
                 -- Shifts take an Int; hence second arg of op is Int
-- See Note [Guarding against silly shifts]
wordShiftRule shift_op
  = do { dflags <- getDynFlags
       ; [e1, Lit (MachInt shift_len)] <- getArgs
       ; case e1 of
           _ | shift_len == 0 
             -> return e1
             | shift_len < 0 || wordSizeInBits dflags < shift_len
             -> return (mkRuntimeErrorApp rUNTIME_ERROR_ID wordPrimTy 
                                        ("Bad shift length" ++ show shift_len))
           Lit (MachWord x)
             -> liftMaybe $ wordResult dflags (x `shift_op` fromInteger shift_len) 
                    -- Do the shift at type Integer, but shift length is Int
           _ -> mzero }

wordSizeInBits :: DynFlags -> Integer
wordSizeInBits dflags = toInteger (platformWordSize (targetPlatform dflags) `shiftL` 3)

--------------------------
floatOp2 :: (Rational -> Rational -> Rational)
         -> DynFlags -> Literal -> Literal
         -> Maybe (Expr CoreBndr)
floatOp2 op dflags (MachFloat f1) (MachFloat f2)
  = Just (mkFloatVal dflags (f1 `op` f2))
floatOp2 _ _ _ _ = Nothing

--------------------------
doubleOp2 :: (Rational -> Rational -> Rational)
          -> DynFlags -> Literal -> Literal
          -> Maybe (Expr CoreBndr)
doubleOp2 op dflags (MachDouble f1) (MachDouble f2)
  = Just (mkDoubleVal dflags (f1 `op` f2))
doubleOp2 _ _ _ _ = Nothing

--------------------------
-- This stuff turns
--      n ==# 3#
-- into
--      case n of
--        3# -> True
--        m  -> False
--
-- This is a Good Thing, because it allows case-of case things
-- to happen, and case-default absorption to happen.  For
-- example:
--
--      if (n ==# 3#) || (n ==# 4#) then e1 else e2
-- will transform to
--      case n of
--        3# -> e1
--        4# -> e1
--        m  -> e2
-- (modulo the usual precautions to avoid duplicating e1)

litEq :: Bool  -- True <=> equality, False <=> inequality
      -> RuleM CoreExpr
litEq is_eq = msum
  [ do [Lit lit, expr] <- getArgs
       dflags <- getDynFlags
       do_lit_eq dflags lit expr
  , do [expr, Lit lit] <- getArgs
       dflags <- getDynFlags
       do_lit_eq dflags lit expr ]
  where
    do_lit_eq dflags lit expr = do
      guard (not (litIsLifted lit))
      return (mkWildCase expr (literalType lit) intPrimTy
                    [(DEFAULT,    [], val_if_neq),
                     (LitAlt lit, [], val_if_eq)])
      where
        val_if_eq  | is_eq     = trueValInt  dflags
                   | otherwise = falseValInt dflags
        val_if_neq | is_eq     = falseValInt dflags
                   | otherwise = trueValInt  dflags


-- | Check if there is comparison with minBound or maxBound, that is
-- always true or false. For instance, an Int cannot be smaller than its
-- minBound, so we can replace such comparison with False.
boundsCmp :: Comparison -> RuleM CoreExpr
boundsCmp op = do
  dflags <- getDynFlags
  [a, b] <- getArgs
  liftMaybe $ mkRuleFn dflags op a b

data Comparison = Gt | Ge | Lt | Le

mkRuleFn :: DynFlags -> Comparison -> CoreExpr -> CoreExpr -> Maybe CoreExpr
mkRuleFn dflags Gt (Lit lit) _ | isMinBound dflags lit = Just $ falseValInt dflags
mkRuleFn dflags Le (Lit lit) _ | isMinBound dflags lit = Just $ trueValInt  dflags
mkRuleFn dflags Ge _ (Lit lit) | isMinBound dflags lit = Just $ trueValInt  dflags
mkRuleFn dflags Lt _ (Lit lit) | isMinBound dflags lit = Just $ falseValInt dflags
mkRuleFn dflags Ge (Lit lit) _ | isMaxBound dflags lit = Just $ trueValInt  dflags
mkRuleFn dflags Lt (Lit lit) _ | isMaxBound dflags lit = Just $ falseValInt dflags
mkRuleFn dflags Gt _ (Lit lit) | isMaxBound dflags lit = Just $ falseValInt dflags
mkRuleFn dflags Le _ (Lit lit) | isMaxBound dflags lit = Just $ trueValInt  dflags
mkRuleFn _ _ _ _                                       = Nothing

isMinBound :: DynFlags -> Literal -> Bool
isMinBound _      (MachChar c)   = c == minBound
isMinBound dflags (MachInt i)    = i == tARGET_MIN_INT dflags
isMinBound _      (MachInt64 i)  = i == toInteger (minBound :: Int64)
isMinBound _      (MachWord i)   = i == 0
isMinBound _      (MachWord64 i) = i == 0
isMinBound _      _              = False

isMaxBound :: DynFlags -> Literal -> Bool
isMaxBound _      (MachChar c)   = c == maxBound
isMaxBound dflags (MachInt i)    = i == tARGET_MAX_INT dflags
isMaxBound _      (MachInt64 i)  = i == toInteger (maxBound :: Int64)
isMaxBound dflags (MachWord i)   = i == tARGET_MAX_WORD dflags
isMaxBound _      (MachWord64 i) = i == toInteger (maxBound :: Word64)
isMaxBound _      _              = False


-- Note that we *don't* warn the user about overflow. It's not done at
-- runtime either, and compilation of completely harmless things like
--    ((124076834 :: Word32) + (2147483647 :: Word32))
-- would yield a warning. Instead we simply squash the value into the
-- *target* Int/Word range.
intResult :: DynFlags -> Integer -> Maybe CoreExpr
intResult dflags result = Just (mkIntVal dflags result')
    where result' = case platformWordSize (targetPlatform dflags) of
                    4 -> toInteger (fromInteger result :: Int32)
                    8 -> toInteger (fromInteger result :: Int64)
                    w -> panic ("intResult: Unknown platformWordSize: " ++ show w)

wordResult :: DynFlags -> Integer -> Maybe CoreExpr
wordResult dflags result = Just (mkWordVal dflags result')
    where result' = case platformWordSize (targetPlatform dflags) of
                    4 -> toInteger (fromInteger result :: Word32)
                    8 -> toInteger (fromInteger result :: Word64)
                    w -> panic ("wordResult: Unknown platformWordSize: " ++ show w)

inversePrimOp :: PrimOp -> RuleM CoreExpr
inversePrimOp primop = do
  [Var primop_id `App` e] <- getArgs
  matchPrimOpId primop primop_id
  return e

subsumesPrimOp :: PrimOp -> PrimOp -> RuleM CoreExpr
this `subsumesPrimOp` that = do
  [Var primop_id `App` e] <- getArgs
  matchPrimOpId that primop_id
  return (Var (mkPrimOpId this) `App` e)

subsumedByPrimOp :: PrimOp -> RuleM CoreExpr
subsumedByPrimOp primop = do
  [e@(Var primop_id `App` _)] <- getArgs
  matchPrimOpId primop primop_id
  return e

idempotent :: RuleM CoreExpr
idempotent = do [e1, e2] <- getArgs
                guard $ cheapEqExpr e1 e2
                return e1

mkBasicRule :: Name -> Int -> RuleM CoreExpr -> CoreRule
-- Gives the Rule the same name as the primop itself
mkBasicRule op_name n_args rm
  = BuiltinRule { ru_name = occNameFS (nameOccName op_name),
                  ru_fn = op_name,
                  ru_nargs = n_args,
                  ru_try = \ dflags in_scope _ -> runRuleM rm dflags in_scope }

newtype RuleM r = RuleM
  { runRuleM :: DynFlags -> InScopeEnv -> [CoreExpr] -> Maybe r }

instance Functor RuleM where
    fmap = liftM

instance Applicative RuleM where
    pure = return
    (<*>) = ap

instance Monad RuleM where
  return x = RuleM $ \_ _ _ -> Just x
  RuleM f >>= g = RuleM $ \dflags iu e -> case f dflags iu e of
    Nothing -> Nothing
    Just r -> runRuleM (g r) dflags iu e
  fail _ = mzero

instance Alternative RuleM where
    empty = mzero
    (<|>) = mplus

instance MonadPlus RuleM where
  mzero = RuleM $ \_ _ _ -> Nothing
  mplus (RuleM f1) (RuleM f2) = RuleM $ \dflags iu args ->
    f1 dflags iu args `mplus` f2 dflags iu args

instance HasDynFlags RuleM where
    getDynFlags = RuleM $ \dflags _ _ -> Just dflags

liftMaybe :: Maybe a -> RuleM a
liftMaybe Nothing = mzero
liftMaybe (Just x) = return x

liftLit :: (Literal -> Literal) -> RuleM CoreExpr
liftLit f = liftLitDynFlags (const f)

liftLitDynFlags :: (DynFlags -> Literal -> Literal) -> RuleM CoreExpr
liftLitDynFlags f = do
  dflags <- getDynFlags
  [Lit lit] <- getArgs
  return $ Lit (f dflags lit)

removeOp32 :: RuleM CoreExpr
#if WORD_SIZE_IN_BITS == 32
removeOp32 = do
  [e] <- getArgs
  return e
#else
removeOp32 = mzero
#endif

getArgs :: RuleM [CoreExpr]
getArgs = RuleM $ \_ _ args -> Just args

getInScopeEnv :: RuleM InScopeEnv
getInScopeEnv = RuleM $ \_ iu _ -> Just iu

-- return the n-th argument of this rule, if it is a literal
-- argument indices start from 0
getLiteral :: Int -> RuleM Literal
getLiteral n = RuleM $ \_ _ exprs -> case drop n exprs of
  (Lit l:_) -> Just l
  _ -> Nothing

unaryLit :: (DynFlags -> Literal -> Maybe CoreExpr) -> RuleM CoreExpr
unaryLit op = do
  dflags <- getDynFlags
  [Lit l] <- getArgs
  liftMaybe $ op dflags (convFloating dflags l)

binaryLit :: (DynFlags -> Literal -> Literal -> Maybe CoreExpr) -> RuleM CoreExpr
binaryLit op = do
  dflags <- getDynFlags
  [Lit l1, Lit l2] <- getArgs
  liftMaybe $ op dflags (convFloating dflags l1) (convFloating dflags l2)

binaryCmpLit :: (forall a . Ord a => a -> a -> Bool) -> RuleM CoreExpr
binaryCmpLit op = do
  dflags <- getDynFlags
  binaryLit (\_ -> cmpOp dflags op)

leftIdentity :: Literal -> RuleM CoreExpr
leftIdentity id_lit = leftIdentityDynFlags (const id_lit)

rightIdentity :: Literal -> RuleM CoreExpr
rightIdentity id_lit = rightIdentityDynFlags (const id_lit)

identity :: Literal -> RuleM CoreExpr
identity lit = leftIdentity lit `mplus` rightIdentity lit

leftIdentityDynFlags :: (DynFlags -> Literal) -> RuleM CoreExpr
leftIdentityDynFlags id_lit = do
  dflags <- getDynFlags
  [Lit l1, e2] <- getArgs
  guard $ l1 == id_lit dflags
  return e2

rightIdentityDynFlags :: (DynFlags -> Literal) -> RuleM CoreExpr
rightIdentityDynFlags id_lit = do
  dflags <- getDynFlags
  [e1, Lit l2] <- getArgs
  guard $ l2 == id_lit dflags
  return e1

identityDynFlags :: (DynFlags -> Literal) -> RuleM CoreExpr
identityDynFlags lit = leftIdentityDynFlags lit `mplus` rightIdentityDynFlags lit

leftZero :: (DynFlags -> Literal) -> RuleM CoreExpr
leftZero zero = do
  dflags <- getDynFlags
  [Lit l1, _] <- getArgs
  guard $ l1 == zero dflags
  return $ Lit l1

rightZero :: (DynFlags -> Literal) -> RuleM CoreExpr
rightZero zero = do
  dflags <- getDynFlags
  [_, Lit l2] <- getArgs
  guard $ l2 == zero dflags
  return $ Lit l2

zeroElem :: (DynFlags -> Literal) -> RuleM CoreExpr
zeroElem lit = leftZero lit `mplus` rightZero lit

equalArgs :: RuleM ()
equalArgs = do
  [e1, e2] <- getArgs
  guard $ e1 `cheapEqExpr` e2

nonZeroLit :: Int -> RuleM ()
nonZeroLit n = getLiteral n >>= guard . not . isZeroLit

-- When excess precision is not requested, cut down the precision of the
-- Rational value to that of Float/Double. We confuse host architecture
-- and target architecture here, but it's convenient (and wrong :-).
convFloating :: DynFlags -> Literal -> Literal
convFloating dflags (MachFloat  f) | not (gopt Opt_ExcessPrecision dflags) =
   MachFloat  (toRational (fromRational f :: Float ))
convFloating dflags (MachDouble d) | not (gopt Opt_ExcessPrecision dflags) =
   MachDouble (toRational (fromRational d :: Double))
convFloating _ l = l

guardFloatDiv :: RuleM ()
guardFloatDiv = do
  [Lit (MachFloat f1), Lit (MachFloat f2)] <- getArgs
  guard $ (f1 /=0 || f2 > 0) -- see Note [negative zero]
       && f2 /= 0            -- avoid NaN and Infinity/-Infinity

guardDoubleDiv :: RuleM ()
guardDoubleDiv = do
  [Lit (MachDouble d1), Lit (MachDouble d2)] <- getArgs
  guard $ (d1 /=0 || d2 > 0) -- see Note [negative zero]
       && d2 /= 0            -- avoid NaN and Infinity/-Infinity
-- Note [negative zero] Avoid (0 / -d), otherwise 0/(-1) reduces to
-- zero, but we might want to preserve the negative zero here which
-- is representable in Float/Double but not in (normalised)
-- Rational. (#3676) Perhaps we should generate (0 :% (-1)) instead?

strengthReduction :: Literal -> PrimOp -> RuleM CoreExpr
strengthReduction two_lit add_op = do -- Note [Strength reduction]
  arg <- msum [ do [arg, Lit mult_lit] <- getArgs
                   guard (mult_lit == two_lit)
                   return arg
              , do [Lit mult_lit, arg] <- getArgs
                   guard (mult_lit == two_lit)
                   return arg ]
  return $ Var (mkPrimOpId add_op) `App` arg `App` arg

-- Note [Strength reduction]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- This rule turns floating point multiplications of the form 2.0 * x and
-- x * 2.0 into x + x addition, because addition costs less than multiplication.
-- See #7116

-- Note [What's true and false]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- trueValInt and falseValInt represent true and false values returned by
-- comparison primops for Char, Int, Word, Integer, Double, Float and Addr.
-- True is represented as an unboxed 1# literal, while false is represented
-- as 0# literal.
-- We still need Bool data constructors (True and False) to use in a rule
-- for constant folding of equal Strings

trueValInt, falseValInt :: DynFlags -> Expr CoreBndr
trueValInt  dflags = Lit $ onei  dflags -- see Note [What's true and false]
falseValInt dflags = Lit $ zeroi dflags

trueValBool, falseValBool :: Expr CoreBndr
trueValBool   = Var trueDataConId -- see Note [What's true and false]
falseValBool  = Var falseDataConId

ltVal, eqVal, gtVal :: Expr CoreBndr
ltVal = Var ltDataConId
eqVal = Var eqDataConId
gtVal = Var gtDataConId

mkIntVal :: DynFlags -> Integer -> Expr CoreBndr
mkIntVal dflags i = Lit (mkMachInt dflags i)
mkWordVal :: DynFlags -> Integer -> Expr CoreBndr
mkWordVal dflags w = Lit (mkMachWord dflags w)
mkFloatVal :: DynFlags -> Rational -> Expr CoreBndr
mkFloatVal dflags f = Lit (convFloating dflags (MachFloat  f))
mkDoubleVal :: DynFlags -> Rational -> Expr CoreBndr
mkDoubleVal dflags d = Lit (convFloating dflags (MachDouble d))

matchPrimOpId :: PrimOp -> Id -> RuleM ()
matchPrimOpId op id = do
  op' <- liftMaybe $ isPrimOpId_maybe id
  guard $ op == op'

tagToEnumRule :: RuleM CoreExpr
-- If     data T a = A | B | C
-- then   tag2Enum# (T ty) 2# -->  B ty
tagToEnumRule = do
  [Type ty, Lit (MachInt i)] <- getArgs
  case splitTyConApp_maybe ty of
    Just (tycon, tc_args) | isEnumerationTyCon tycon -> do
      let tag = fromInteger i
          correct_tag dc = (dataConTag dc - fIRST_TAG) == tag
      (dc:rest) <- return $ filter correct_tag (tyConDataCons_maybe tycon `orElse` [])
      ASSERT(null rest) return ()
      return $ mkTyApps (Var (dataConWorkId dc)) tc_args

    -- See Note [tagToEnum#]
    _ -> WARN( True, ptext (sLit "tagToEnum# on non-enumeration type") <+> ppr ty )
         return $ mkRuntimeErrorApp rUNTIME_ERROR_ID ty "tagToEnum# on non-enumeration type"

dataToTagRule :: RuleM CoreExpr
dataToTagRule = a `mplus` b
  where
    a = do
      [Type ty1, Var tag_to_enum `App` Type ty2 `App` tag] <- getArgs
      guard $ tag_to_enum `hasKey` tagToEnumKey
      guard $ ty1 `eqType` ty2
      return tag -- dataToTag (tagToEnum x)   ==>   x
    b = do
      dflags <- getDynFlags
      [_, val_arg] <- getArgs
      in_scope <- getInScopeEnv
      (dc,_,_) <- liftMaybe $ exprIsConApp_maybe in_scope val_arg
      ASSERT( not (isNewTyCon (dataConTyCon dc)) ) return ()
      return $ mkIntVal dflags (toInteger (dataConTag dc - fIRST_TAG))

-- seq# :: forall a s . a -> State# s -> (# State# s, a #)
seqRule :: RuleM CoreExpr
seqRule = do
  [ty_a, Type ty_s, a, s] <- getArgs
  guard $ exprIsHNF a
  return $ mkConApp (tupleCon UnboxedTuple 2)
    [Type (mkStatePrimTy ty_s), ty_a, s, a]

-- spark# :: forall a s . a -> State# s -> (# State# s, a #)
sparkRule :: RuleM CoreExpr
sparkRule = seqRule -- reduce on HNF, just the same
  -- XXX perhaps we shouldn't do this, because a spark eliminated by
  -- this rule won't be counted as a dud at runtime?

builtinRules :: [CoreRule]
-- Rules for non-primops that can't be expressed using a RULE pragma
builtinRules
  = [BuiltinRule { ru_name = fsLit "AppendLitString",
                   ru_fn = unpackCStringFoldrName,
                   ru_nargs = 4, ru_try = \_ _ _ -> match_append_lit },
     BuiltinRule { ru_name = fsLit "EqString", ru_fn = eqStringName,
                   ru_nargs = 2, ru_try = \dflags _ _ -> match_eq_string dflags },
     BuiltinRule { ru_name = fsLit "Inline", ru_fn = inlineIdName,
                   ru_nargs = 2, ru_try = \_ _ _ -> match_inline },
     BuiltinRule { ru_name = fsLit "MagicDict", ru_fn = idName magicDictId,
                   ru_nargs = 4, ru_try = \_ _ _ -> match_magicDict }
     ]
 ++ builtinIntegerRules

builtinIntegerRules :: [CoreRule]
builtinIntegerRules =
 [rule_IntToInteger   "smallInteger"        smallIntegerName,
  rule_WordToInteger  "wordToInteger"       wordToIntegerName,
  rule_Int64ToInteger  "int64ToInteger"     int64ToIntegerName,
  rule_Word64ToInteger "word64ToInteger"    word64ToIntegerName,
  rule_convert        "integerToWord"       integerToWordName       mkWordLitWord,
  rule_convert        "integerToInt"        integerToIntName        mkIntLitInt,
  rule_convert        "integerToWord64"     integerToWord64Name     (\_ -> mkWord64LitWord64),
  rule_convert        "integerToInt64"      integerToInt64Name      (\_ -> mkInt64LitInt64),
  rule_binop          "plusInteger"         plusIntegerName         (+),
  rule_binop          "minusInteger"        minusIntegerName        (-),
  rule_binop          "timesInteger"        timesIntegerName        (*),
  rule_unop           "negateInteger"       negateIntegerName       negate,
  rule_binop_Prim     "eqInteger#"          eqIntegerPrimName       (==),
  rule_binop_Prim     "neqInteger#"         neqIntegerPrimName      (/=),
  rule_unop           "absInteger"          absIntegerName          abs,
  rule_unop           "signumInteger"       signumIntegerName       signum,
  rule_binop_Prim     "leInteger#"          leIntegerPrimName       (<=),
  rule_binop_Prim     "gtInteger#"          gtIntegerPrimName       (>),
  rule_binop_Prim     "ltInteger#"          ltIntegerPrimName       (<),
  rule_binop_Prim     "geInteger#"          geIntegerPrimName       (>=),
  rule_binop_Ordering "compareInteger"      compareIntegerName      compare,
  rule_encodeFloat    "encodeFloatInteger"  encodeFloatIntegerName  mkFloatLitFloat,
  rule_convert        "floatFromInteger"    floatFromIntegerName    (\_ -> mkFloatLitFloat),
  rule_encodeFloat    "encodeDoubleInteger" encodeDoubleIntegerName mkDoubleLitDouble,
  rule_decodeDouble   "decodeDoubleInteger" decodeDoubleIntegerName,
  rule_convert        "doubleFromInteger"   doubleFromIntegerName   (\_ -> mkDoubleLitDouble),
  rule_rationalTo     "rationalToFloat"     rationalToFloatName     mkFloatExpr,
  rule_rationalTo     "rationalToDouble"    rationalToDoubleName    mkDoubleExpr,
  rule_binop          "gcdInteger"          gcdIntegerName          gcd,
  rule_binop          "lcmInteger"          lcmIntegerName          lcm,
  rule_binop          "andInteger"          andIntegerName          (.&.),
  rule_binop          "orInteger"           orIntegerName           (.|.),
  rule_binop          "xorInteger"          xorIntegerName          xor,
  rule_unop           "complementInteger"   complementIntegerName   complement,
  rule_Int_binop      "shiftLInteger"       shiftLIntegerName       shiftL,
  rule_Int_binop      "shiftRInteger"       shiftRIntegerName       shiftR,
  -- See Note [Integer division constant folding] in libraries/base/GHC/Real.lhs
  rule_divop_one      "quotInteger"         quotIntegerName         quot,
  rule_divop_one      "remInteger"          remIntegerName          rem,
  rule_divop_one      "divInteger"          divIntegerName          div,
  rule_divop_one      "modInteger"          modIntegerName          mod,
  rule_divop_both     "divModInteger"       divModIntegerName       divMod,
  rule_divop_both     "quotRemInteger"      quotRemIntegerName      quotRem,
  -- These rules below don't actually have to be built in, but if we
  -- put them in the Haskell source then we'd have to duplicate them
  -- between all Integer implementations
  rule_XToIntegerToX "smallIntegerToInt"       integerToIntName    smallIntegerName,
  rule_XToIntegerToX "wordToIntegerToWord"     integerToWordName   wordToIntegerName,
  rule_XToIntegerToX "int64ToIntegerToInt64"   integerToInt64Name  int64ToIntegerName,
  rule_XToIntegerToX "word64ToIntegerToWord64" integerToWord64Name word64ToIntegerName,
  rule_smallIntegerTo "smallIntegerToWord"   integerToWordName     Int2WordOp,
  rule_smallIntegerTo "smallIntegerToFloat"  floatFromIntegerName  Int2FloatOp,
  rule_smallIntegerTo "smallIntegerToDouble" doubleFromIntegerName Int2DoubleOp
  ]
    where rule_convert str name convert
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_Integer_convert convert }
          rule_IntToInteger str name
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_IntToInteger }
          rule_WordToInteger str name
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_WordToInteger }
          rule_Int64ToInteger str name
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_Int64ToInteger }
          rule_Word64ToInteger str name
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_Word64ToInteger }
          rule_unop str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_Integer_unop op }
          rule_binop str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_binop op }
          rule_divop_both str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_divop_both op }
          rule_divop_one str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_divop_one op }
          rule_Int_binop str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_Int_binop op }
          rule_binop_Prim str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_binop_Prim op }
          rule_binop_Ordering str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_binop_Ordering op }
          rule_encodeFloat str name op
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_Integer_Int_encodeFloat op }
          rule_decodeDouble str name
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_decodeDouble }
          rule_XToIntegerToX str name toIntegerName
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_XToIntegerToX toIntegerName }
          rule_smallIntegerTo str name primOp
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 1,
                           ru_try = match_smallIntegerTo primOp }
          rule_rationalTo str name mkLit
           = BuiltinRule { ru_name = fsLit str, ru_fn = name, ru_nargs = 2,
                           ru_try = match_rationalTo mkLit }

---------------------------------------------------
-- The rule is this:
--      unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
--      =  unpackFoldrCString# "foobaz" c n

match_append_lit :: [Expr CoreBndr] -> Maybe (Expr CoreBndr)
match_append_lit [Type ty1,
                    Lit (MachStr s1),
                    c1,
                    Var unpk `App` Type ty2
                             `App` Lit (MachStr s2)
                             `App` c2
                             `App` n
                   ]
  | unpk `hasKey` unpackCStringFoldrIdKey &&
    c1 `cheapEqExpr` c2
  = ASSERT( ty1 `eqType` ty2 )
    Just (Var unpk `App` Type ty1
                   `App` Lit (MachStr (s1 `BS.append` s2))
                   `App` c1
                   `App` n)

match_append_lit _ = Nothing

---------------------------------------------------
-- The rule is this:
--      eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2

match_eq_string :: DynFlags -> [Expr CoreBndr] -> Maybe (Expr CoreBndr)
match_eq_string _ [Var unpk1 `App` Lit (MachStr s1),
                        Var unpk2 `App` Lit (MachStr s2)]
  | unpk1 `hasKey` unpackCStringIdKey,
    unpk2 `hasKey` unpackCStringIdKey
  = Just (if s1 == s2 then trueValBool else falseValBool)

match_eq_string _ _ = Nothing


---------------------------------------------------
-- The rule is this:
--      inline f_ty (f a b c) = <f's unfolding> a b c
-- (if f has an unfolding, EVEN if it's a loop breaker)
--
-- It's important to allow the argument to 'inline' to have args itself
-- (a) because its more forgiving to allow the programmer to write
--       inline f a b c
--   or  inline (f a b c)
-- (b) because a polymorphic f wll get a type argument that the
--     programmer can't avoid
--
-- Also, don't forget about 'inline's type argument!
match_inline :: [Expr CoreBndr] -> Maybe (Expr CoreBndr)
match_inline (Type _ : e : _)
  | (Var f, args1) <- collectArgs e,
    Just unf <- maybeUnfoldingTemplate (realIdUnfolding f)
             -- Ignore the IdUnfoldingFun here!
  = Just (mkApps unf args1)

match_inline _ = Nothing


-- See Note [magicDictId magic] in `basicTypes/MkId.lhs`
-- for a description of what is going on here.
match_magicDict :: [Expr CoreBndr] -> Maybe (Expr CoreBndr)
match_magicDict [Type _, Var wrap `App` Type a `App` Type _ `App` f, x, y ]
  | Just (fieldTy, _)   <- splitFunTy_maybe $ dropForAlls $ idType wrap
  , Just (dictTy, _)    <- splitFunTy_maybe fieldTy
  , Just dictTc         <- tyConAppTyCon_maybe dictTy
  , Just (_,_,co)       <- unwrapNewTyCon_maybe dictTc
  = Just
  $ f `App` Cast x (mkSymCo (mkUnbranchedAxInstCo Representational co [a]))
      `App` y

match_magicDict _ = Nothing

-------------------------------------------------
-- Integer rules
--   smallInteger  (79::Int#)  = 79::Integer
--   wordToInteger (79::Word#) = 79::Integer
-- Similarly Int64, Word64

match_IntToInteger :: RuleFun
match_IntToInteger _ id_unf fn [xl]
  | Just (MachInt x) <- exprIsLiteral_maybe id_unf xl
  = case idType fn of
    FunTy _ integerTy ->
        Just (Lit (LitInteger x integerTy))
    _ ->
        panic "match_IntToInteger: Id has the wrong type"
match_IntToInteger _ _ _ _ = Nothing

match_WordToInteger :: RuleFun
match_WordToInteger _ id_unf id [xl]
  | Just (MachWord x) <- exprIsLiteral_maybe id_unf xl
  = case idType id of
    FunTy _ integerTy ->
        Just (Lit (LitInteger x integerTy))
    _ ->
        panic "match_WordToInteger: Id has the wrong type"
match_WordToInteger _ _ _ _ = Nothing

match_Int64ToInteger :: RuleFun
match_Int64ToInteger _ id_unf id [xl]
  | Just (MachInt64 x) <- exprIsLiteral_maybe id_unf xl
  = case idType id of
    FunTy _ integerTy ->
        Just (Lit (LitInteger x integerTy))
    _ ->
        panic "match_Int64ToInteger: Id has the wrong type"
match_Int64ToInteger _ _ _ _ = Nothing

match_Word64ToInteger :: RuleFun
match_Word64ToInteger _ id_unf id [xl]
  | Just (MachWord64 x) <- exprIsLiteral_maybe id_unf xl
  = case idType id of
    FunTy _ integerTy ->
        Just (Lit (LitInteger x integerTy))
    _ ->
        panic "match_Word64ToInteger: Id has the wrong type"
match_Word64ToInteger _ _ _ _ = Nothing

-------------------------------------------------
match_Integer_convert :: Num a
                      => (DynFlags -> a -> Expr CoreBndr)
                      -> RuleFun
match_Integer_convert convert dflags id_unf _ [xl]
  | Just (LitInteger x _) <- exprIsLiteral_maybe id_unf xl
  = Just (convert dflags (fromInteger x))
match_Integer_convert _ _ _ _ _ = Nothing

match_Integer_unop :: (Integer -> Integer) -> RuleFun
match_Integer_unop unop _ id_unf _ [xl]
  | Just (LitInteger x i) <- exprIsLiteral_maybe id_unf xl
  = Just (Lit (LitInteger (unop x) i))
match_Integer_unop _ _ _ _ _ = Nothing

match_Integer_binop :: (Integer -> Integer -> Integer) -> RuleFun
match_Integer_binop binop _ id_unf _ [xl,yl]
  | Just (LitInteger x i) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  = Just (Lit (LitInteger (x `binop` y) i))
match_Integer_binop _ _ _ _ _ = Nothing

-- This helper is used for the quotRem and divMod functions
match_Integer_divop_both
   :: (Integer -> Integer -> (Integer, Integer)) -> RuleFun
match_Integer_divop_both divop _ id_unf _ [xl,yl]
  | Just (LitInteger x t) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  , y /= 0
  , (r,s) <- x `divop` y
  = Just $ mkConApp (tupleCon UnboxedTuple 2)
                    [Type t,
                     Type t,
                     Lit (LitInteger r t),
                     Lit (LitInteger s t)]
match_Integer_divop_both _ _ _ _ _ = Nothing

-- This helper is used for the quot and rem functions
match_Integer_divop_one :: (Integer -> Integer -> Integer) -> RuleFun
match_Integer_divop_one divop _ id_unf _ [xl,yl]
  | Just (LitInteger x i) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  , y /= 0
  = Just (Lit (LitInteger (x `divop` y) i))
match_Integer_divop_one _ _ _ _ _ = Nothing

match_Integer_Int_binop :: (Integer -> Int -> Integer) -> RuleFun
match_Integer_Int_binop binop _ id_unf _ [xl,yl]
  | Just (LitInteger x i) <- exprIsLiteral_maybe id_unf xl
  , Just (MachInt y)      <- exprIsLiteral_maybe id_unf yl
  = Just (Lit (LitInteger (x `binop` fromIntegral y) i))
match_Integer_Int_binop _ _ _ _ _ = Nothing

match_Integer_binop_Prim :: (Integer -> Integer -> Bool) -> RuleFun
match_Integer_binop_Prim binop dflags id_unf _ [xl, yl]
  | Just (LitInteger x _) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  = Just (if x `binop` y then trueValInt dflags else falseValInt dflags)
match_Integer_binop_Prim _ _ _ _ _ = Nothing

match_Integer_binop_Ordering :: (Integer -> Integer -> Ordering) -> RuleFun
match_Integer_binop_Ordering binop _ id_unf _ [xl, yl]
  | Just (LitInteger x _) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  = Just $ case x `binop` y of
             LT -> ltVal
             EQ -> eqVal
             GT -> gtVal
match_Integer_binop_Ordering _ _ _ _ _ = Nothing

match_Integer_Int_encodeFloat :: RealFloat a
                              => (a -> Expr CoreBndr)
                              -> RuleFun
match_Integer_Int_encodeFloat mkLit _ id_unf _ [xl,yl]
  | Just (LitInteger x _) <- exprIsLiteral_maybe id_unf xl
  , Just (MachInt y)      <- exprIsLiteral_maybe id_unf yl
  = Just (mkLit $ encodeFloat x (fromInteger y))
match_Integer_Int_encodeFloat _ _ _ _ _ = Nothing

---------------------------------------------------
-- constant folding for Float/Double
--
-- This turns
--      rationalToFloat n d
-- into a literal Float, and similarly for Doubles.
--
-- it's important to not match d == 0, because that may represent a
-- literal "0/0" or similar, and we can't produce a literal value for
-- NaN or +-Inf
match_rationalTo :: RealFloat a
                 => (a -> Expr CoreBndr)
                 -> RuleFun
match_rationalTo mkLit _ id_unf _ [xl, yl]
  | Just (LitInteger x _) <- exprIsLiteral_maybe id_unf xl
  , Just (LitInteger y _) <- exprIsLiteral_maybe id_unf yl
  , y /= 0
  = Just (mkLit (fromRational (x % y)))
match_rationalTo _ _ _ _ _ = Nothing

match_decodeDouble :: RuleFun
match_decodeDouble _ id_unf fn [xl]
  | Just (MachDouble x) <- exprIsLiteral_maybe id_unf xl
  = case idType fn of
    FunTy _ (TyConApp _ [integerTy, intHashTy]) ->
        case decodeFloat (fromRational x :: Double) of
        (y, z) ->
            Just $ mkConApp (tupleCon UnboxedTuple 2)
                            [Type integerTy,
                             Type intHashTy,
                             Lit (LitInteger y integerTy),
                             Lit (MachInt (toInteger z))]
    _ ->
        panic "match_decodeDouble: Id has the wrong type"
match_decodeDouble _ _ _ _ = Nothing

match_XToIntegerToX :: Name -> RuleFun
match_XToIntegerToX n _ _ _ [App (Var x) y]
  | idName x == n
  = Just y
match_XToIntegerToX _ _ _ _ _ = Nothing

match_smallIntegerTo :: PrimOp -> RuleFun
match_smallIntegerTo primOp _ _ _ [App (Var x) y]
  | idName x == smallIntegerName
  = Just $ App (Var (mkPrimOpId primOp)) y
match_smallIntegerTo _ _ _ _ _ = Nothing