Ömer Sinan Ağacan authored Sep 13, 2019 and Marge Bot committed Oct 01, 2019

Simon writes:

Currently we check for a type arg rather than isTyCoArg.   This in turn
makes INLINE things look bigger than they should be, and stops them
being inlined into boring contexts when they perfectly well could be.
E.g.

    f x = g <refl> x
    {-# INLINE g #-}

    ... (map (f x) xs) ...

The context is boring, so don't inline unconditionally.  But f's RHS is
no bigger than its call, provided you realise that the coercion argument
is ultimately cost-free.

This happens in practice for $WHRefl. It's not a big deal: at most it
means we have an extra function call overhead.  But it's untidy, and
actually worse than what happens without an INLINE pragma.

Fixes #17182

This makes 0.0% change in nofib binary sizes.