I will try creating a minimal example and open a ticket for the inlining problem, the one I am sure about.
-harendra On 8 September 2017 at 18:35, Simon Peyton Jones <[email protected]> wrote: > *I know that this is not an easy request*, but can either of you produce > a small example that demonstrates your problem? If so, please open a > ticket. > > > > I don’t like hearing about people having to use trial and error with > INLINE or SPECIALISE pragmas. But I can’t even begin to solve the problem > unless I can reproduce it. > > > > Simon > > > > *From:* ghc-devs [mailto:[email protected]] *On Behalf Of *Harendra > Kumar > *Sent:* 08 September 2017 13:50 > *To:* Mikolaj Konarski <[email protected]> > *Cc:* [email protected] > *Subject:* Re: Performance degradation when factoring out common code > > > > I should also point out that I saw performance improvements by manually > factoring out and propagating some common expressions to outer loops in > performance sensitive paths. Now I have made this a habit to do this > manually. Not sure if something like this has also been fixed with that > ticket or some other ticket. > > > > -harendra > > > > On 8 September 2017 at 17:34, Harendra Kumar <[email protected]> > wrote: > > Thanks Mikolaj! I have seen some surprising behavior quite a few times > recently and I was wondering whether GHC should do better. In one case I > had to use SPECIALIZE very aggressively, in another version of the same > code it worked well without that. I have been doing a lot of trial and > error with the INLINE/NOINLINE pragmas to figure out what the right > combination is. Sometimes it just feels like black magic, because I cannot > find a rationale to explain the behavior. I am not sure if there are any > more such problems lurking in, perhaps this is an area where some > improvement looks possible. > > > > -harendra > > > > > > On 8 September 2017 at 17:10, Mikolaj Konarski <[email protected]> > wrote: > > Hello, > > I've had a similar problem that's been fixed in 8.2.1: > > https://ghc.haskell.org/trac/ghc/ticket/12603 > > You can also use some extreme global flags, such as > > ghc-options: -fexpose-all-unfoldings -fspecialise-aggressively > > to get most the GHC subtlety and shyness out of the way > when experimenting. > > Good luck > Mikolaj > > > > > On Fri, Sep 8, 2017 at 11:21 AM, Harendra Kumar > <[email protected]> wrote: > > Hi, > > > > I have this code snippet for the bind implementation of a Monad: > > > > AsyncT m >>= f = AsyncT $ \_ stp yld -> > > let run x = (runAsyncT x) Nothing stp yld > > yield a _ Nothing = run $ f a > > yield a _ (Just r) = run $ f a <> (r >>= f) > > in m Nothing stp yield > > > > I want to have multiple versions of this implementation parameterized by > a > > function, like this: > > > > bindWith k (AsyncT m) f = AsyncT $ \_ stp yld -> > > let run x = (runAsyncT x) Nothing stp yld > > yield a _ Nothing = run $ f a > > yield a _ (Just r) = run $ f a `k` (bindWith k r f) > > in m Nothing stp yield > > > > And then the bind function becomes: > > > > (>>=) = bindWith (<>) > > > > But this leads to a performance degradation of more than 10%. inlining > does > > not help, I tried INLINE pragma as well as the "inline" GHC builtin. I > > thought this should be a more or less straightforward replacement making > the > > second version equivalent to the first one. But apparently there is > > something going on here that makes it perform worse. > > > > I did not look at the core, stg or asm yet. Hoping someone can quickly > > comment on it. Any ideas why is it so? Can this be worked around somehow? > > > > Thanks, > > Harendra > > > > > _______________________________________________ > > ghc-devs mailing list > > [email protected] > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > <https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmail.haskell.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc-devs&data=02%7C01%7Csimonpj%40microsoft.com%7C5ff3c69fb9d447c47b5908d4f6b832de%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636404718373134824&sdata=zyHYozym6TzL61Tq5CSERjqhKlxr%2ByV0j%2FyHtxmXmVE%3D&reserved=0> > > > > > > >
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