[GHC] #11160: New exhaustiveness checker breaks ghcirun004

Simon Peyton Jones simonpj at microsoft.com
Fri Dec 4 13:38:02 UTC 2015

No let’s not revert.  But:

·         Please put a list of the tickets (there are several) on the wiki page (where is the wiki page?)

o   perf/compiler/T783

o   #11163: perf/compiler/T5642


·         Let’s have a flag to skip overlap testing so that there is always a workaround

·         Are you happy to continue to work on these perf issues?


From: George Karachalias [mailto:george.karachalias at gmail.com]
Sent: 04 December 2015 09:41
To: Simon Peyton Jones <simonpj at microsoft.com>
Subject: Re: [GHC] #11160: New exhaustiveness checker breaks ghcirun004


On Fri, Dec 4, 2015 at 10:34 AM, GHC <ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>> wrote:
Comment (by simonpj):

 Very fast response thank you.

 Your commit message is very informative.  Did you include the same
 information in a `Note` in the code, so that we don't lose the information

I haven't yet but I can. Actually, I wanted to ask you something. At the moment
I pass all the normal tests but I fail some performance tests. They do compile but there is a
deviation from the expected and HEAD is broken. For the additional expressive power I expected
some more memory and time. For example, for perf/compiler/T783.hs which has 500 guards in a
single function definition I take ~5 sec to compile but the deviation in allocated bytes is 753%,
compared to what the "expected" is. I feel terrible since we are really close to the freeze and I
think I am stalling everyone. I know of no good way to reduce memory consumption without
losing substantial expressivity. Do you think I shall revert?

things you own end up owning you
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