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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">It’s absolutely the case that bang patterns etc tell the caller what to do, but the function CANNOT ASSUME that its argument is evaluated. Reason: higher order functions.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">I think that the way to allow functions that can assume their arg is evaluated is through types: see
<a href="http://research.microsoft.com/~simonpj/papers/strict-core/tacc-hs09.pdf">
Type are calling conventions</a>. But it’d be a fairly big deal to implement.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">
<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>Ryan Newton<br>
<b>Sent:</b> 23 October 2015 14:54<br>
<b>To:</b> ghc-devs@haskell.org; Ömer Sinan Ağacan; Ryan Scott; Chao-Hong Chen; Johan Tibell<br>
<b>Subject:</b> Better calling conventions for strict functions (bang patterns)?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Hi all,<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
With module-level Strict and StrictData pragmas coming soon, one obvious question is what kind of the code quality GHC can achieve for strict programs.<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
When it came up in discussion in our research group we realized we didn't actually know whether the bang patterns, `f !x`, on function arguments were enforced by caller or callee.<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Here's a Gist that shows the compilation of a trivial function:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#795DA3">foo</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">::</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">Maybe</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">Int</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">-></span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">Int</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"><o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333">foo !x =<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">case</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> x
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">of</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">Just</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> y -> y<o:p></o:p></span></p>
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<o:p> </o:p></p>
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<a href="https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fgist.github.com%2frrnewton%2f1ac722189c65f26fe9ac&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7cb006dcdbfe834ebb6c1e08d2dbb16c03%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=qxrT8r1VSP97xQUF2qqkLlxEtSGi9VOzfmORl25W%2fWY%3d">https://gist.github.com/rrnewton/1ac722189c65f26fe9ac</a><o:p></o:p></p>
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<o:p> </o:p></p>
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If that function is compiled to *assume* its input is in WHNF, it should be just as efficient as the isomorphic MLton/OCaml code, right? It only needs to branch on the tag, do a field dereference, and return.<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
But as you can see from the STG and CMM generated, foo <i>does indeed</i> enter the thunk, adding an extra indirect jump. Here's the body:<o:p></o:p></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aY:<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">if</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> ((Sp + -</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">)
< SpLim) </span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aZ;
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">else</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3b0;<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aZ:<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#969896">// nop</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"><o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> R1 = PicBaseReg + foo_closure;<o:p></o:p></span></p>
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<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">call</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (I64[BaseReg -
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">])(R2, R1) args:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, res:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">0</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, upd:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
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<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L28">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC28">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3b0:<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L29">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC29">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> I64[Sp -
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">] = PicBaseReg + block_c3aO_info;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L30">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC30">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> R1 = R2;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L31">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC31">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> Sp = Sp -
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L32">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC32">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">if</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (R1 &
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">7</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> !=
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">0</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">)
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aO;
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">else</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aP;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L33">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC33">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aP:<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L34">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC34">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">call</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (I64[R1])(R1) returns to c3aO, args:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, res:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, upd:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L35">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC35">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aO:<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L36">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC36">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">if</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (R1 &
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">7</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> >=
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">2</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">)
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aW;
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">else</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">
</span><span style="font-size:9.0pt;font-family:Consolas;color:#A71D5D">goto</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aX;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L37">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC37">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aW:<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L38">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC38">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> R1 = P64[R1 +
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">6</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">] & (-</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">);<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L39">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC39">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> Sp = Sp +
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L40">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC40">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">call</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (I64[R1])(R1) args:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, res:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">0</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, upd:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L41">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC41">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> c3aX:<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L42">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC42">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> R1 = PicBaseReg + lvl_r39S_closure;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L43">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC43">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> Sp = Sp +
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td width="50" nowrap="" valign="top" style="width:37.5pt;border:solid #EEEEEE 1.0pt;border-top:none;padding:0cm 7.5pt 0cm 7.5pt;min-width:50px;color:rgba(0,0,0,0.298039)" id="file-_optimizedcmm-c-L44">
</td>
<td valign="top" style="padding:0cm 7.5pt 0cm 7.5pt;word-wrap:normal;overflow:visible" id="file-_optimizedcmm-c-LC44">
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:13.65pt">
<span style="font-size:9.0pt;font-family:Consolas;color:#333333"> </span>
<span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">call</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333"> (I64[R1])(R1) args:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, res:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">0</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">, upd:
</span><span style="font-size:9.0pt;font-family:Consolas;color:#0086B3">8</span><span style="font-size:9.0pt;font-family:Consolas;color:#333333">;<o:p></o:p></span></p>
</td>
</tr>
</tbody>
</table>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
<o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
<o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
The call inside c3aP is entering "x" as a thunk, which also incurs all of the stack limit check code. I believe that IF the input could be assumed to be in WHNF, everything above the label "c3aO" could be omitted.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
<o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
So... if GHC is going to be a fabulous pure <i>and</i> imperative language, and a fabulous lazy
<i>and</i> strict compiler/runtime.. is there some work we can do here to improve this situation? Would the following make sense:<o:p></o:p></p>
</div>
<div>
<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Put together a benchmark suite of all-strict programs with Strict/StrictData (compare a few benchmark's generated code to MLton, if time allows)<o:p></o:p></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
Modify GHC to change calling conventions for bang patterns -- caller enforces WHNF rather than callee. Existing strictness/demand/cardinality analysis would stay the same.<o:p></o:p></li></ul>
</div>
<div>
<p class="MsoNormal">Unless there's something I'm really missing here, the result should be that you can have a whole chain of strict function calls, each of which knows its arguments and the arguments it passes to its callees are all in WHNF, without ever
generating thunk-entry sequences.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Thanks for your time,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> -Ryan<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</div>
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