Do not claim that -O2 does not do better than -O
authorJoachim Breitner <mail@joachim-breitner.de>
Wed, 30 Mar 2016 14:09:36 +0000 (16:09 +0200)
committerJoachim Breitner <mail@joachim-breitner.de>
Wed, 30 Mar 2016 16:07:12 +0000 (18:07 +0200)
commit3d245bf5255ebfb72813596fa93b9051f7518321
treecaef6b33ffa4e532dd8e0b90075be00898fceaa7
parent1757dd8ebed0732018319e43e6468b868a6aceeb
Do not claim that -O2 does not do better than -O

when in fact it does. This was pointed out by Johannes Bechberger and
supported with seemingly statistically sound evidence in his Bachelor
thesis: Of the benchmark shootout programs, 80% benefit significantly by
switchtng from -O to -O2.

See https://uqudy.serpens.uberspace.de/blog/2016/02/08/ghc-performance-over-time/
for a few raw numbers.

Differential Revision: https://phabricator.haskell.org/D2065
docs/users_guide/using-optimisation.rst