Cond.hs

module GHC.CmmToAsm.X86.Cond (
        Cond(..),
        condToUnsigned,
        maybeFlipCond,
        maybeInvertCond
)

where

import GHC.Prelude

data Cond
        = ALWAYS        -- What's really used? ToDo
        | EQQ           -- je/jz -> zf=1
        | GE            -- jge   -> sf=of
        | GEU           -- ae    -> cf=0
        | GTT           -- jg    -> zf=0 && sf=of
        | GU            -- ja    -> cf=0 && zf=0
        | LE            -- jle   -> zf=1 || sf/=of
        | LEU           -- jbe   -> cf=1 || zf=1
        | LTT           -- jl    -> sf/=of
        | LU            -- jb    -> cf=1
        | NE            -- jne   -> zf=0
        | NEG           -- js    -> sf=1
        | POS           -- jns   -> sf=0
        | CARRY         -- jc    -> cf=1
        | OFLO          -- jo    -> of=1
        | PARITY        -- jp    -> pf=1
        | NOTPARITY     -- jnp   -> pf=0
        deriving Eq

condToUnsigned :: Cond -> Cond
condToUnsigned GTT = GU
condToUnsigned LTT = LU
condToUnsigned GE  = GEU
condToUnsigned LE  = LEU
condToUnsigned x   = x

-- | @maybeFlipCond c@ returns @Just c'@ if it is possible to flip the
-- arguments to the conditional @c@, and the new condition should be @c'@.
maybeFlipCond :: Cond -> Maybe Cond
maybeFlipCond cond  = case cond of
        EQQ   -> Just EQQ
        NE    -> Just NE
        LU    -> Just GU
        GU    -> Just LU
        LEU   -> Just GEU
        GEU   -> Just LEU
        LTT   -> Just GTT
        GTT   -> Just LTT
        LE    -> Just GE
        GE    -> Just LE
        _other -> Nothing

-- | If we apply @maybeInvertCond@ to the condition of a jump we turn
-- jumps taken into jumps not taken and vice versa.
--
-- Careful! If the used comparison and the conditional jump
-- don't match the above behaviour will NOT hold.
-- When used for FP comparisons this does not consider unordered
-- numbers.
-- Also inverting twice might return a synonym for the original condition.
maybeInvertCond :: Cond -> Maybe Cond
maybeInvertCond cond  = case cond of
        ALWAYS  -> Nothing
        EQQ     -> Just NE
        NE      -> Just EQQ

        NEG     -> Just POS
        POS     -> Just NEG

        GEU     -> Just LU
        LU      -> Just GEU

        GE      -> Just LTT
        LTT     -> Just GE

        GTT     -> Just LE
        LE      -> Just GTT

        GU      -> Just LEU
        LEU     -> Just GU

        --GEU "==" NOTCARRY, they are synonyms
        --at the assembly level
        CARRY   -> Just GEU

        OFLO    -> Nothing

        PARITY  -> Just NOTPARITY
        NOTPARITY -> Just PARITY