<div dir="ltr">Yup, I think I have it figured out. Will just need to find the time to write the remaining code.</div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Sep 22, 2015 at 10:13 AM, Simon Peyton Jones <span dir="ltr"><<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Johan<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Sorry I’ve been buried. Let’s fix a time for a Skype call if you’d like to chat about this stuff.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Quick response to the below. I think that afterwards we want it to look like this:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">post-unarise<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">f = \r [ ds1::Int# ds2::Ptr ]<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"> case ds1 of<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"> 0# -> <rhs with ds2 in place of x_svo><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"> 1# -> <rhs><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">ds2 is the thing that contains either an Int or a char; ds1 is the tag that distinguishes htem.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Simon<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><u></u> <u></u></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"> Johan Tibell [mailto:<a href="mailto:johan.tibell@gmail.com" target="_blank">johan.tibell@gmail.com</a>]
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<b>Sent:</b> 14 September 2015 17:03<br>
<b>To:</b> Ryan Newton; Simon Peyton Jones<br>
<b>Cc:</b> Simon Marlow; <a href="mailto:ghc-devs@haskell.org" target="_blank">ghc-devs@haskell.org</a><br>
<b>Subject:</b> Re: Converting unboxed sum types in StgCmm<u></u><u></u></span></p>
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I've given this a yet some more thought. Given this simple core program:<u></u><u></u></p>
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<u></u> <u></u></p>
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<span style="font-family:"Courier New"">f [InlPrag=NOINLINE] :: (#|#) Int Char -> Int</span><u></u><u></u></p>
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<span style="font-family:"Courier New"">[GblId, Arity=1, Str=DmdType]</span><u></u><u></u></p>
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<span style="font-family:"Courier New"">f =</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> \ (ds_dmE :: (#|#) Int Char) -></span><u></u><u></u></p>
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<span style="font-family:"Courier New""> case ds_dmE of _ [Occ=Dead] {</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#_|#) x_amy -> x_amy;</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#|_#) ipv_smK -> patError @ Int "UnboxedSum.hs:5:1-15|function f"#</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> }</span><u></u><u></u></p>
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<u></u> <u></u></p>
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We will get this stg pre-unarise:<u></u><u></u></p>
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<u></u> <u></u></p>
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<span style="font-family:"Courier New"">unarise</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> [f [InlPrag=NOINLINE] :: (#|#) Int Char -> Int</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> [GblId, Arity=1, Str=DmdType, Unf=OtherCon []] =</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> \r srt:SRT:[0e :-> patError] [ds_svm]</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> case ds_svm of _ [Occ=Dead] {</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#_|#) x_svo [Occ=Once] -> x_svo;</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#|_#) _ [Occ=Dead] -> patError "UnboxedSum.hs:5:1-15|function f"#;</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> };]</span><u></u><u></u></p>
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<u></u> <u></u></p>
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What do we want it to look like afterwards? I currently, have this, modeled after unboxed tuples:<u></u><u></u></p>
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<u></u> <u></u></p>
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<span style="font-family:"Courier New"">post-unarise:</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> [f [InlPrag=NOINLINE] :: (#|#) Int Char -> Int</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> [GblId, Arity=1, Str=DmdType, Unf=OtherCon []] =</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> \r srt:SRT:[0e :-> patError] [ds_gvu ds_gvv]</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> case (#_|#) [ds_gvu ds_gvv] of _ [Occ=Dead] { -- <-- WHAT SHOULD GO HERE?</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#_|#) x_svo [Occ=Once] -> x_svo;</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> (#|_#) _ [Occ=Dead] -> patError "UnboxedSum.hs:5:1-15|function f"#;</span><u></u><u></u></p>
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<span style="font-family:"Courier New""> };]</span><u></u><u></u></p>
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<u></u> <u></u></p>
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Here I have performed the same rewriting of the scrutinee in the case statement as for unboxed tuples, but note that this doesn't quite work, as we don't know which data constructor to apply in "..." in case ... of. In the case of tuples it's easy; there is
only one.<u></u><u></u></p>
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<u></u> <u></u></p>
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It seems to me that we just want to rewrite the case altogether into something that looks at the tag field of the data constructor. Also, in stg we use the same DataCon as in core, but after stg the unboxed sum case really only has one constructor (one with
the union of all the fields), which makes it awkward to reuse the original DataCon.<u></u><u></u></p>
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<u></u> <u></u></p>
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On Mon, Sep 14, 2015 at 7:27 AM, Ryan Newton <<a href="mailto:rrnewton@gmail.com" target="_blank">rrnewton@gmail.com</a>> wrote:<u></u><u></u></p>
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data RepType = UbxTupleRep [UnaryType]<br>
| UbxSumRep [UnaryType]<br>
| UnaryRep UnaryType<u></u><u></u></li></ul>
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<p class="MsoNormal">Not, fully following, but ... this reptype business is orthogonal to whether you add a normal type to the STG level that models anonymous, untagged unions, right? <u></u><u></u></p>
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<p class="MsoNormal">That is, when using Any for pointer types, they could use indicative phantom types, like "Any (Union Bool Char)", even if there's not full support for doing anything useful with (Union Bool Char) by itself. Maybe the casting machinery
could greenlight a cast from Any (Union Bool Char) to Bool at least?<u></u><u></u></p>
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<p class="MsoNormal">There's already the unboxed union itself, (|# #|) , but that's different than a pointer to a union of types...<u></u><u></u></p>
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