Make Eq type class single method

[Oleg Grenrus]

It might be they are not required.

In example like

{-# OPTIONS_GHC -ddump-simpl -dsuppress-all #-}

import System.Environment
import Data.Word

main :: IO ()
main = do
    [x',y'] <- getArgs
    let x, y :: Word
        x = read x'
        y = read y'

    print (not (x == y))

GHC is smart enough to just swap the branches, relevant optimized core
looks like

case x_a4Tc of { W# x2_a3Wb ->
case x1_X4Ua of { W# y_a3Wf ->
case eqWord# x2_a3Wb y_a3Wf of {
  __DEFAULT -> $fShowBool2;
  1# -> $fShowBool4
}
}
};

where `$fShowBool*` are (probably, I haven't checked) printing True or
False.

I.e. expressions which are "case (not x) of True -> ..., False -> ..."
optimize well,
early enough. (IIRC that's the example used for case-of-case optimization).

- Oleg

On 20.10.2021 19.55, Sven Panne wrote:
> Am Mi., 20. Okt. 2021 um 18:51 Uhr schrieb Oleg Grenrus
> <oleg.grenrus at iki.fi <mailto:oleg.grenrus at iki.fi>>:
>
>     [...] Also, we coudl add builtin rewrite rules, rewriting not
>     (eqInt8 x y)
>     to neInt8 x y if some benchmarks show that it would be beneficial.
>
>
> Hopefully such peephole optimizations are done much more generally
> further down the compilation pipeline, otherwise we will have more
> serious performance problems than the removal of (/=) from Eq. ;-)
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