#5421: <<loop>> in withMVar (reproducible, but with large test case)
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Reporter: JohnMillikin | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.2.1 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: Incorrect result at runtime
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A user of one of my libraries is reporting that it fails with the message
{{{<<loop>>}}} when compiled in GHC 7.2.1. The error is coming from
{{{withMVar}}}, and is reproducible.
Unfortunately, the problem is *very* tricky to reproduce. Attempting to
debug it (such as adding print statements, re-ordering operations, or
removing unrelated code) will cause it to vanish. Therefore, the test case
I have attached is a full Cabal project with build instructions. Nearly
every line of code is required, and changing or removing them hides the
error again.
Changes which can hide the problem:
* Altering or removing the startup messages (even the version number).
* Removing unused attributes from types.
* Removing unused error checking.
* Using {{{_ <- char 'a'}}} instead of {{{void (char 'a')}}}.
* Moving a function from one module to another.
* Simplifying loops which only run over one element.
* Building it all at once with {{{--make}}}, and not a separate {{{cabal-
dev install}}} step.
* Building 'Main' with {{{-O2}}}.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5421>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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