-O/-O2 causes program to run too slow

[David Spies]

Ok, so I found that it was an instance of this:
https://ghc.haskell.org/trac/ghc/ticket/1168
and I read through this whole thread:
https://www.haskell.org/pipermail/glasgow-haskell-users/2008-February/014259.html

I don't understand the state-hack optimization.  It's clearly not safe and
I'm not convinced that it actually is an optimization.  In what
circumstances does the state-hack identify a single-entry function that
can't be identified as single-entry by some other (safe) method?


On Sun, Dec 7, 2014 at 10:52 AM, David Spies <dnspies at gmail.com> wrote:

> I have a program I wrote to submit for the Car Game problem on Kattis:
> https://open.kattis.com/problems/cargame
> but it runs over the 5-second time-limit
>
> I downloaded the test data and found that on GHC 7.8.3, if I switch from
> -O2 to -O0, it runs three times faster (almost certainly fast enough for
> Kattis to accept).  Can someone tell me what's going on?  Is this a bug?
>
>
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