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<p class="MsoNormal"><span style="font-size:12.0pt">It sounds good to me – I have not dug into the details but it seems to have had enough scrutiny.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Note that it <b>replaces one primop with another</b>, with the old one being re-defined as an ordinary function for back-compat. The proposal does not just add an extra primop. Right?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">I’m supportive, albeit not very well informed.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><br>
Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-steering-committee <ghc-steering-committee-bounces@haskell.org>
<b>On Behalf Of </b>Simon Marlow<br>
<b>Sent:</b> 04 July 2018 10:19<br>
<b>To:</b> ghc-steering-committee@haskell.org<br>
<b>Subject:</b> [ghc-steering-committee] Replace atomicModifyMutVar# (#149), recommendation: accept<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<a href="https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F149&data=02%7C01%7Csimonpj%40microsoft.com%7Caf6991e741df405fd5a308d5e18f477f%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636662927862631135&sdata=biPMT2Nj9w7jJHUSdHU3eaHMS9wOzIbm7w%2B6txXLpeE%3D&reserved=0" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/149</a><o:p></o:p></p>
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<o:p> </o:p></p>
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This proposal is essentially an optimisation to the atomicModifyMutVar# primitive. I won't repeat the details here, but it amounts to moving one of the thunks produced by atomicModifyMutVar# out of the primop and into the atomicModifyIORef wrapper. The advantage
is that in the case of the strict version of the wrapper, atomicModifyIORef', this extra thunk is eliminated entirely, rather than being created by the primop and then immediately evaluated by the wrapper.<o:p></o:p></p>
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<o:p> </o:p></p>
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I propose we accept the proposal to add the new primop in section 2.1, along with the straightforward additions proposed in sections 2.2 and 2.3. (the old primop will be removed, but can be defined in GHC.Exts as a wrapper around the new primop for backwards
compat)<o:p></o:p></p>
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<o:p> </o:p></p>
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However, the additions to the Data.IORef library should be considered by the libraries committee separately. (there are naming issues to be resolved in particular).<o:p></o:p></p>
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<o:p> </o:p></p>
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Cheers<o:p></o:p></p>
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Simon<o:p></o:p></p>
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