[Q] Inlining done: evtRead

[Simon Peyton Jones]

|  a) If the INLINE pragma is such a commandment, why don't we respect it with
|  -O0?

We ignore pragmas with -O0.

|  b) Would it be sensible to only inline in scrutinee (`case <id> of
|  ...`) context, to avoid duplication? After all it's the guts of the value
|  we are interested in, not the whole package.

That's what happened before but see Note [Honour INLINE on 0-ary bindings] in CoreUnfold and Trac #15578 

|  c) Could a global CSE pass pick up the floated-out value and revert it to
|  the original imported identifier?

CSE does not currently do CSE with imported unfoldings.  It would be possible, but perhaps expensive, to do so.

|  d) Or should be simply remove the INLINE pragmas from the library (0-ary
|  objects)? Possibly changing to INLINABLE?

I have absolutely no idea why it is there.  I bet that removing it is the right thing to do.

S

|  -----Original Message-----
|  From: Gabor Greif <ggreif at gmail.com>
|  Sent: 08 January 2019 10:06
|  To: Mikolaj Konarski <mikolaj at well-typed.com>
|  Cc: Simon Peyton Jones <simonpj at microsoft.com>; ghc-devs <ghc-
|  devs at haskell.org>
|  Subject: Re: [Q] Inlining done: evtRead
|  
|  Thanks Mikolaj and Simon,
|  
|  this explains it. I'll study the related ticket next. Still, the floating-
|  out related duplication aspect looks like a problem, or would you disagree?
|  I mean,
|  
|  a) If the INLINE pragma is such a commandment, why don't we respect it with
|  -O0?
|  b) Would it be sensible to only inline in scrutinee (`case <id> of
|  ...`) context, to avoid duplication? After all it's the guts of the value
|  we are interested in, not the whole package.
|  c) Could a global CSE pass pick up the floated-out value and revert it to
|  the original imported identifier?
|  d) Or should be simply remove the INLINE pragmas from the library (0-ary
|  objects)? Possibly changing to INLINABLE?
|  
|  Just thinking out loud, as this appears like a pessimisation to me.
|  
|  Cheers,
|  
|      Gabor
|  
|  On 1/8/19, Mikolaj Konarski <mikolaj at well-typed.com> wrote:
|  > On Tue, Jan 8, 2019 at 2:10 AM Gabor Greif <ggreif at gmail.com> wrote:
|  >>
|  >> Hmm, yes. So why wasn't GHC 8.4 doing this? Did some commit fix the
|  >> inliner to respect the pragma?
|  >
|  > Yes:
|  > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitl
|  > ab.haskell.org%2Fghc%2Fghc%2Fcommit%2Fb9b1f99954e69f23e9647d00e048938d
|  > 5509ec14&data=02%7C01%7Csimonpj%40microsoft.com%7Ca24c2089a67d4377
|  > 39aa08d67550e5a5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63682538
|  > 7644348465&sdata=qhyHG6VD1%2B9Mkrjwzt7DcTYFVPhtVosdTdhSCJwExSA%3D&
|  > amp;reserved=0
|  >
|  > But it's not on 8.6 branch (yet?).
|  >