In my commit of 24 May I got this boolean condition
back to front:

    tryWW non_rec fn_id rhs
      | not (isNeverInlinePrag inline_prag)
      =  -- Don't split things that will never be inlined

The 'not' is obviously wrong!  As a result virtually nothing
is being worker-wrapper'd

How this has survived for more than two weeks beats me.