Bug: GHC creates incorrect code which throws <<loop>>

Simon Peyton Jones simonpj at microsoft.com
Thu Apr 23 08:10:17 UTC 2015


#10218 is fully fixed, so are we good on this one now?

Simon

|  -----Original Message-----
|  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
|  Richard Eisenberg
|  Sent: 01 April 2015 17:52
|  To: Yongqian Li
|  Cc: ghc-devs at haskell.org
|  Subject: Re: Bug: GHC creates incorrect code which throws <<loop>>
|  
|  Thanks for posting the bug and bringing it to our attention. The reason
|  the report may not have gotten attention is that I believe this falls
|  in Simon PJ's domain, and he's on holiday right now. I took a quick
|  look, but I haven't a clue about this area of GHC, so there's not much
|  I can contribute. Unless someone else out there knows much about black-
|  holing, you may have to wait a bit. Sorry!
|  
|  Richard
|  
|  On Mar 31, 2015, at 9:48 PM, Yongqian Li <yongqli at kerrmetric.com>
|  wrote:
|  
|  > Hi all,
|  >
|  > I wanted to bring to your attention this bug,
|  > https://ghc.haskell.org/trac/ghc/ticket/10218 , which I filed about
|  > two days ago but hasn't gotten any replies to yet.
|  >
|  >
|  > In my opinion, this is a rather serious bug since GHC is producing
|  > incorrect code. While there is a workaround, it makes my program take
|  > about 2 hours to compile.
|  >
|  >
|  > Since reporting the bug, I've also seen "strange closure type"
|  > exceptions, which I believe are also caused by this bug, although I
|  do
|  > not have a test case. Based on my limited understanding of GHC
|  > internals, I suspect the problem lies in how type class dictionaries
|  > are looked up at run time, as the problem disappears if GHC can fully
|  > resolve the types.
|  >
|  >
|  > Can others see if they can reproduce this bug? If there is any way I
|  > can help, please let me know.
|  >
|  >
|  > Sincerely,
|  > Yongqian Li
|  > _______________________________________________
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