[GHC] #14521: Infinite loop at runtime

[GHC]

#14521: Infinite loop at runtime
-------------------------------------+-------------------------------------
        Reporter:  OlivierSohn       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.3
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Old description:

> Hello,
>
> in https://github.com/OlivierSohn/hamazed/issues/1 I describe the
> following issue:
>
> **(Edit : the same behaviour exists with ghc 8.2.2)**
>
> When compiling on OSX with optimizations (`stack clean && stack build`
> using resolver `lts-9.12` (ghc 8.0.2)), the program loops infinitely
> (400% CPU, and execution is blocked) when an animation is triggered in
> the game. When compiling without optimizations, there is not this bug.
>
> The bug is visible in the full game at this commit :
> https://github.com/OlivierSohn/hamazed/commit/9f25223ef0502f91cd9633654bdb172f714c3920
> (to reproduce, shoot at a number in the game)
>
> And this commit shows a program with minimal code to reproduce the issue
> :
> https://github.com/OlivierSohn/hamazed/commit/30b0f703565a4150d686a36a4dfe9d36ce5989f1
>
> The expected output of the program is
>
> {{{
> Before rendering animations
> animation is rendered
> After rendering animations
> }}}
>
> What I observe is
>
> {{{
> Before rendering animations
> }}}
>
> I found several ways to circumvent the problem, wrote them in the code to
> help debugging.
>
> Also, here is my stack version if it matters:
> {{{
> stack version: `1.3.2, Git revision
> 3f675146590da4f3edf768b89355f798229da2a5 (4395 commits) x86_64
> hpack-0.15.0`
> }}}
>
> Thank you,
> Olivier

New description:

 Hello,

 For this program : https://github.com/OlivierSohn/hamazed/tree/repro-
 ghc-14521-A

 The expected output is:

 {{{
 Before rendering animations
 animation is rendered
 After rendering animations
 }}}

 What I observe is when compiling with ghc 8.0.2 or 8.2.2, with
 optimizations:

 {{{
 Before rendering animations
 }}}

 I found several ways to circumvent the bug, and documented each one in the
 source code.

 Can someone take a look? Is my program an invalid program that was not
 detected by the compiler?

 Thank you,
 Olivier

--

Comment (by OlivierSohn):

 I update the description to reference the branch of the repro case and not
 a particular commit, and to be more concise.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14521#comment:17>
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