SPECIALISE INLINE pragma

[Simon Peyton Jones]

|  I didn't know the bit about INLINE being ignored on a loop-breaker
|  with no warning and no way of changing the loop-breaker.

GHC tries hard NOT to choose an INLINE function as a loop breaker.  But if you write

f x = if ... then 0 else (f x')
{-# INLINE f #-}

then the only possible loop breaker is 'f', so GHC has to choose it. 

What else would you suggest?  What puzzling behaviour do you have in mind?

Simon

|  -----Original Message-----
|  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
|  Mikolaj Konarski
|  Sent: 20 March 2017 23:41
|  To: Matthew Pickering <matthewtpickering at gmail.com>
|  Cc: GHC developers <ghc-devs at haskell.org>
|  Subject: Re: SPECIALISE INLINE pragma
|  
|  > On the same topic, I also wrote a blog post simply explaining the
|  > essential things to know about the inliner and specialiser as I
|  don't
|  > think they are generally appreciated. Comments welcome!
|  >
|  > http://mpickering.github.io/posts/2017-03-20-inlining-and-
|  specialisati
|  > on.html
|  
|  LGTM. I'd propose to link to this from GHC manual.
|  
|  I didn't know the bit about INLINE being ignored on a loop-breaker
|  with no warning and no way of changing the loop-breaker. That probably
|  explains puzzling and counter-intuitive results of some alternative
|  layouts of INLINEs in the computation-intensive parts of my code, at
|  least since the time I provide unfoldings for all functions and so
|  discounts don't help GHC in picking the intended loop-breaker.
|  And I don't think this ignoring of the programmer's intent wrt INLINE
|  is documented in the usual places.
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