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[GHC] #13429: Optimizer produces Core with an infinite <<loop>>

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[GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
           Reporter:  lehins         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect result
  Unknown/Multiple                   |  at runtime
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 While using vector package to implement convolution and supplying `-O1` or
 `-02` to ghc compilation results in core with an infinite loop. In order
 to trigger this behavior at least two modules is required. Attached is the
 minimal setup that I could come up with, that demonstrates the issue. Here
 is the stack trace:

 {{{
 $ stack --install-ghc --resolver lts-8.3 exec -- ghc -O1 -prof -fprof-auto
 main.hs && ./main +RTS -xc
 [1 of 2] Compiling Loop             ( Loop.hs, Loop.o )
 [2 of 2] Compiling Main             ( main.hs, main.o )
 Linking main ...
 *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace:
   Main.CAF
   --> evaluated by: Main.main,
   called from Main.CAF
   --> evaluated by: Loop.toKernel.\,
   called from Data.Vector.Fusion.Util.>>=,
   called from Loop.toKernel,
   called from Main.main,
   called from Main.CAF
   --> evaluated by: Data.Vector.Fusion.Util.>>=,
   called from Loop.toKernel,
   called from Main.main,
   called from Main.CAF
 *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace:
   Main.CAF
 main: <<loop>>
 }}}


 At first I though that it might be a bug in a vector package, which is
 still a possibility, but since I was not able to observe that issue with
 ghc-7.8.4, I decided to open an ticket here. I tested attached code with
 all of subsequent released ghc versions (7.10.1 - 8.0.2), which resulted
 in the infinite loop.

 Worth noting that sometimes, when recompilation of only the `main.hs` file
 is enforced, program starts to work as expected. Here is an example:


 {{{
 $ stack --resolver ghc-7.10.3 exec --package vector-0.11.0.0 --package
 primitive-0.6.1.0 -- ghc -O1 main.hs && ./main
 [1 of 2] Compiling Loop             ( Loop.hs, Loop.o )
 [2 of 2] Compiling Main             ( main.hs, main.o )
 Linking main ...
 main: <<loop>>
 $ touch main.hs
 $ stack --resolver ghc-7.10.3 exec --package vector-0.11.0.0 --package
 primitive-0.6.1.0 -- ghc -O1 main.hs && ./main
 [2 of 2] Compiling Main             ( main.hs, main.o )
 Linking main ...
 <Image 1x1>
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by lehins):

 * Attachment "Loop.hs" added.

 Minimal implementation that triggers the issue.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by lehins):

 * Attachment "main.hs" added.

 correlation has to be invoked from a separate module.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by lehins):

 * Attachment "RUNS.md" added.

 Various versions that compilation was attempted with.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  new => merge
 * milestone:   => 7.10.4


Comment:

 This appears to be fixed in 8.2 with `vector-0.12.0.0`. Unfortunately,
 it's quite unclear what fixed it and working this our will likely be a
 significant investment of effort.

 Given that there is unlikely to be an 8.0.3, I think it's pretty unlikely
 that we will fix this in the 8.0 series but I'm marking this as `merge`
 regardless.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:1>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by lehins):

 I was able to reproduce this issue using lists instead of vector package,
 confirming that it is indeed a bug in ghc.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:2>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by dfeuer):

 Replying to [comment:2 lehins]:
 > I was able to reproduce this issue using lists instead of vector
 package, confirming that it is indeed a bug in ghc.

 Could you attach that reproduction here? I suspect this might be worth
 investigating a bit more, despite the pain, to make sure that the
 underlying problem was actually fixed and not just buried.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:3>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by lehins):

 * Attachment "Loop.2.hs" added.

 Same implementation triggering a bug using List instead of vector.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 Thanks. I confirmed that the bug was present in HEAD as of Feb 1 but is
 not present any more.

 Something rather curious is that the bug cannot be reproduced when there
 are `.hi` and `.o` files present from a previous compilation with the same
 version of ghc, even when passing `-fforce-recomp`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:4>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by lehins):

 It's good to hear that it is fixed. It would be nice to know what is the
 actual cause and a reliable way to avoid this bug with ghc-8.0.2 and
 older, so anybody who stumbles upon it has a workaround. It feels like it
 has something to do with class constraints and inlining, but what exactly
 is still a mystery to me.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:5>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"be8122ab72aeec509b5ce4b4f05fbc5cdb77bf5a/ghc"
 be8122ab/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="be8122ab72aeec509b5ce4b4f05fbc5cdb77bf5a"
 testsuite: Add testcase for #13429
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:6>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  merge => new


Comment:

 While this appears to be fixed, Simon would like to know what precisely
 fixed it.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:7>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 I've verified that commit 2effe18ab51d66474724d38b20e49cc1b8738f60 (The
 Early Inline Patch) was what fixed this.

 Somewhat related: the
 [https://ghc.haskell.org/trac/ghc/changeset/be8122ab72aeec509b5ce4b4f05fbc5cdb77bf5a/ghc
 commit] which added this program as a regression test isn't actually
 //running// the compiled program, so it's not verifying if it's looping or
 not. Surely this isn't intended?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:8>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

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#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Yes, the test should run.

 We still need to know why it looped before. The early-inline patch should
 not, of itself, have changed that!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:9>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

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In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by lehins):

 For what it's worth, I figured out a reliable way to avoid the bug, namely
 adding an extra constraint `Array X e`.

 So changing the type signature of `correlate` to:

 `correlate :: (Array X e, Array cs e) => Image X e -> Image cs e -> Image
 cs e`

 can be used as a trick for working around the bug.

 Not sure if it is relevant, but maybe it will help in narrowing down a
 possible cause.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:10>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

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In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * Attachment "Loop.hs-reduced" added.

 Reduced version of Loop

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

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In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * Attachment "main.hs-reduced" added.

 main to go with reduced Loop

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by dfeuer):

 I am getting the very strong feeling that the problem has a lot to do with
 `UndecidableInstances`, constraint simplification, or something in that
 general area. Simplifying constraints by hand seems to make the bug go
 away. Removing the `INLINE` annotation seems to do so as well. I created a
 reduced test case, which hopefully will be simpler to work on.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:11>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * cc: dfeuer (added)
 * failure:  Incorrect result at runtime => Runtime crash
 * priority:  normal => high


--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429#comment:12>
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Re: [GHC] #13429: Optimizer produces Core with an infinite <<loop>>

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#13429: Optimizer produces Core with an infinite <<loop>>
-------------------------------------+-------------------------------------
        Reporter:  lehins            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  7.10.4
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * Attachment "LoopReduced2.hs" added.


--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429>
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