On November 11, 2017 10:03:37 PM EST, Joachim Breitner <mail@joachim-breitner.de> wrote:Hi Alan,
the combined effect of
commit e3ec2e7ae94524ebd111963faf34b84d942265b4
WIP on combined Step 1 and 3 for Trees That Grow, HsExpr
and
commit 438dd1cbba13d35f3452b4dcef3f94ce9a216905
WIP on Doing a combined Step 1 and 3 for Trees That Grow
causes a 15% regression in the time it takes to build GHC, according to
https://perf.haskell.org/ghc/#compare/fe6848f544c2a14086bcef388c46f4070c22d287/e3ec2e7ae94524ebd111963faf34b84d942265b4
Is that a known, expected and accepted regression?
Joachim
I noted this on D4177 and discussed the effect with Alan. Indeed there is quite a sizeable regression in compilation time but thankfully this is not because GHC itself is slower. Rather, it simply requires more work to compile. I did a set of nofib runs with and without the first TTG patch and found that compiler allocations remained essentially unchanged.A 15% regression in the compilation time of GHC is indeed hard to stomach but Alan had said that much of this will likely disappear in the future. If this is the case then a temporary regression is in my opinion acceptable.
Cheers,
Manuel