Bogus calculation of bottoming arity

In CoreArity we see

andArityType (ABot n1) (ABot n2) = ABot (n1 `min` n2)

If you look at the documentation for ABot (which is about functions that are guaranteed to diverge) this is obviously bogus. The min should be max!

Here's a test case:

{-# LANGUAGE MagicHash #-}

module Foo( f ) where
import GHC.Prim

f True  = raise# True
f False = \p q -> raise# False

If you compile (with GHC 8.0) -ddump-simpl you'll see

f :: forall a p1 p2. Bool -> p2 -> p1 -> a
[GblId, Arity=1, Caf=NoCafRefs, Str=<L,U>x]

That Str=<L,U>x is totally bogus; it claims that f will always diverge given one argument.

The fix is easy.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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