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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">I know that this is not an easy request</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">,
but can either of you produce a small example that demonstrates your problem? If so, please open a ticket.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">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.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> ghc-devs [mailto:ghc-devs-bounces@haskell.org]
<b>On Behalf Of </b>Harendra Kumar<br>
<b>Sent:</b> 08 September 2017 13:50<br>
<b>To:</b> Mikolaj Konarski <mikolaj.konarski@gmail.com><br>
<b>Cc:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> Re: Performance degradation when factoring out common code<o:p></o:p></span></p>
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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.<o:p></o:p></p>
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-harendra<o:p></o:p></p>
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On 8 September 2017 at 17:34, Harendra Kumar <<a href="mailto:harendra.kumar@gmail.com" target="_blank">harendra.kumar@gmail.com</a>> wrote:<o:p></o:p></p>
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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.<span class="hoenzb"><span style="color:#888888"><o:p></o:p></span></span></p>
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<span style="color:#888888">-harendra<o:p></o:p></span></p>
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On 8 September 2017 at 17:10, Mikolaj Konarski <<a href="mailto:mikolaj.konarski@gmail.com" target="_blank">mikolaj.konarski@gmail.com</a>> wrote:<o:p></o:p></p>
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Hello,<br>
<br>
I've had a similar problem that's been fixed in 8.2.1:<br>
<br>
<a href="https://ghc.haskell.org/trac/ghc/ticket/12603" target="_blank">https://ghc.haskell.org/trac/ghc/ticket/12603</a><br>
<br>
You can also use some extreme global flags, such as<br>
<br>
ghc-options: -fexpose-all-unfoldings -fspecialise-aggressively<br>
<br>
to get most the GHC subtlety and shyness out of the way<br>
when experimenting.<br>
<br>
Good luck<br>
Mikolaj<o:p></o:p></p>
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<br>
<br>
<br>
On Fri, Sep 8, 2017 at 11:21 AM, Harendra Kumar<br>
<<a href="mailto:harendra.kumar@gmail.com" target="_blank">harendra.kumar@gmail.com</a>> wrote:<br>
> Hi,<br>
><br>
> I have this code snippet for the bind implementation of a Monad:<br>
><br>
> AsyncT m >>= f = AsyncT $ \_ stp yld -><br>
> let run x = (runAsyncT x) Nothing stp yld<br>
> yield a _ Nothing = run $ f a<br>
> yield a _ (Just r) = run $ f a <> (r >>= f)<br>
> in m Nothing stp yield<br>
><br>
> I want to have multiple versions of this implementation parameterized by a<br>
> function, like this:<br>
><br>
> bindWith k (AsyncT m) f = AsyncT $ \_ stp yld -><br>
> let run x = (runAsyncT x) Nothing stp yld<br>
> yield a _ Nothing = run $ f a<br>
> yield a _ (Just r) = run $ f a `k` (bindWith k r f)<br>
> in m Nothing stp yield<br>
><br>
> And then the bind function becomes:<br>
><br>
> (>>=) = bindWith (<>)<br>
><br>
> But this leads to a performance degradation of more than 10%. inlining does<br>
> not help, I tried INLINE pragma as well as the "inline" GHC builtin. I<br>
> thought this should be a more or less straightforward replacement making the<br>
> second version equivalent to the first one. But apparently there is<br>
> something going on here that makes it perform worse.<br>
><br>
> I did not look at the core, stg or asm yet. Hoping someone can quickly<br>
> comment on it. Any ideas why is it so? Can this be worked around somehow?<br>
><br>
> Thanks,<br>
> Harendra<br>
><o:p></o:p></p>
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> _______________________________________________<br>
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