Compilation time

[Deest, Gaël]

Hi all,

As you are probably well aware, GHC performance has been a growing concern
over the last few years. Many Haskell programmers complain that build time
has significantly increased over the last few releases. However, to our
knowledge, there isn't much data available to substantiate this claim and
the severity of these problems is not well known.

That's why we would like to bring some anecdotal evidence to your attention
that seems to indicate really major performance regressions. We stumbled
upon the CI of the data-reify package, which is built against all GHC
releases since 2010 :

https://travis-ci.org/ku-fpg/data-reify

tl;dr: Build time has gone from 1 min 32s for GHC 7.0 to 4 min 35s for GHC
8.2. The 8.2 release alone seems to have increased compilation time by
almost 2 minutes, with the current development branch bringing only minor
performance improvements.

Of course, this single data point is not sufficient to establish how severe
and widespread these problems are. More data could probably be gathered
from other packages. However, it certainly matches our (subjective)
experience and we felt important to report it to you.

Regards,

-- 
Gaël Deest
Tweag I/O
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