join points and stream fusion?

[Simon Peyton Jones]

Thank you!

|  -----Original Message-----
|  From: Christian Höner zu Siederdissen [mailto:choener at bioinf.uni-
|  leipzig.de]
|  Sent: 28 April 2017 00:14
|  To: Simon Peyton Jones <simonpj at microsoft.com>
|  Cc: glasgow-haskell-users at haskell.org
|  Subject: Re: join points and stream fusion?
|  
|  Sorry,
|  
|  with the addendum, I have constructed a very small example:
|  https://ghc.haskell.org/trac/ghc/ticket/13623
|  
|  This is new with ghc 8.2-rc1 and does not show up earlier.
|  
|  Viele Gruesse,
|  Christian
|  
|  * Simon Peyton Jones <simonpj at microsoft.com> [28.04.2017 00:35]:
|  > I'm afraid I don't have enough context to understand this thread.
|  >
|  > Could you offer a concrete example (as small as possible), and
|  explain how to reproduce the problem you are seeing.  Don't forget to
|  give the compiler version you are using, and any libraries you depend
|  on (as few as poss).
|  >
|  > Is this a regression? I.e. did some earlier version of GHC do better
|  on the exact same code?
|  >
|  > Maybe open a Trac ticket.
|  >
|  > Thanks
|  >
|  > Simon
|  >
|  > | -----Original Message-----
|  > | From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
|  > | bounces at haskell.org] On Behalf Of Christian Höner zu Siederdissen
|  > | Sent: 27 April 2017 23:10
|  > | To: glasgow-haskell-users at haskell.org
|  > | Subject: Re: join points and stream fusion?
|  > |
|  > | As an addendum,
|  > |
|  > | I think what causes this is the following. I have a function
|  > | (|||) xs ys = \lu ij -> xs lu ij Stream.++ ys lu ij xs and ys are
|  > | two stream-generating functions and (Stream.++) concatenates
|  > | streams. In the example I have four streams:
|  > | xs_1 ||| xs_2 ||| xs_3 ||| xs_4
|  > |
|  > | However, here I end up with a join point on (++). Further
|  evidenced
|  > | (?) by the curious occurance of s1uf4 ... (Left (Left (Left
|  ...))).
|  > | Additional calls then are (Left (Left (Right ))) and so on.
|  > |
|  > | It would be really good if (|||) is *not* turned into a join
|  point.
|  > |
|  > | Best,
|  > | Christian
|  > |
|  > | * Christian Höner zu Siederdissen <choener at bioinf.uni-leipzig.de>
|  > | [27.04.2017 23:30]:
|  > | > Dear all,
|  > | >
|  > | > have some of you experienced bad code generation in ghc-8.2-rc1
|  in
|  > | > combination with stream fusion from the vector package?
|  > | >
|  > | > Unfortunately, the problem occurs with ADPfusion code which
|  means
|  > | > no simple example, but I'm asking because of the following core
|  below.
|  > | >
|  > | > In ghc-8.0 I have nice core, here however constructor
|  > | > specialization has not happened, neither with the Left/Right nor
|  with the SPEC.
|  > | >
|  > | > The running time in ghc-8.0 is 2.6 seconds, in rc-1 10.9
|  seconds.
|  > | >
|  > | > Best,
|  > | > Christian
|  > | >
|  > | > joinrec {
|  > | >   $wfoldlM'_loop2_s1uf4
|  > | >   $wfoldlM'_loop2_s1uf4 w_s1ueX ww1_s1uf2 w1_s1ueZ
|  > | >     = case w_s1ueX of { __DEFAULT ->
|  > | >       case w1_s1ueZ of {
|  > | >         Left sa_au90 ->
|  > | >           case sa_au90 of {
|  > | >             Left sa1_XuNq ->
|  > | >               case sa1_XuNq of {
|  > | >                 Left sa2_XuNe ->
|  > | >                   case sa2_XuNe of {
|  > | >                     SL s2_alTo k_alTp ->
|  > | >                       case k_alTp of {
|  > | >                         __DEFAULT ->
|  > | >                           jump $wfoldlM'_loop2_s1uf4
|  > | >                             SPEC ww1_s1uf2 lvl211_s1IDG;
|  > | >                         1# ->
|  > | >                           jump $wfoldlM'_loop2_s1uf4
|  > | >                             SPEC ww1_s1uf2 (Left (Left (Left (SR
|  > | > s2_alTo))))
|  > | >
|  > | > _______________________________________________
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