Avoid useless w/w split, take 2
This commit:
commit c6faa42bfb954445c09c5680afd4fb875ef03758
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date: Mon Mar 9 10:20:42 2020 +0000
Avoid useless w/w split
This patch is just a tidy-up for the post-strictness-analysis
worker wrapper split. Consider
f x = x
Strictnesss analysis does not lead to a w/w split, so the
obvious thing is to leave it 100% alone. But actually, because
the RHS is small, we ended up adding a StableUnfolding for it.
There is some reason to do this if we choose /not/ do to w/w
on the grounds that the function is small. See
Note [Don't w/w inline small non-loop-breaker things]
But there is no reason if we would not have done w/w anyway.
This patch just moves the conditional to later. Easy.
turns out to have a bug in it. Instead of /moving/ the conditional,
I /duplicated/ it. Then in a subsequent unrelated tidy-up
(087ac4eb
) I removed the second (redundant) test!
This patch does what I originally intended.
There is also a small refactoring in GHC.Core.Unfold, to make the code clearer, but with no change in behaviour.
Fixes #17917 (closed) (again)