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<p>Hi Eliot,</p>
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<p>> <span>Interesting! No, there’s no swap as yet. If SqueakV3PlusClosures has an unused bytecode I’d say go for it. (SistaV1 definitely has unused bytecodes).</span></p>
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<p><span>Great to hear this! I would be glad to join the implementation of a new bytecode :-)</span></p>
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<p><span>> </span><span style="font-size: 12pt;">pop and store temp: N (where N gets to sp - 1)</span><span></span></p>
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<div>Which bytecode are you referring to? #<span><span>genStoreTemp:</span>? This sounds indeed hacky ...</span></div>
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<div><span>Just another question about bytecodes: Do we currently have any tools for exploring and playing around with the bytecodes? I would love to do say something like</span></div>
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<div><span>Encoder default generateMethod: [:stack :encoder |</span></div>
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<div><span> encoder genPushReceiver.</span></div>
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<div><span> encoder genReturnTop].</span></div>
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<div><span>But afaik, at the moment I have to manipulate the implementation of #<span>emitCodeForValue:encoder: or so if I would like to test something new. Am I missing any existing tools to do so?</span></span></div>
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(Imagine if you could write your own bytecodes directly into a CodeHolder ... :D)</div>
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Best,</div>
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Christoph<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Von:</b> Squeak-dev <squeak-dev-bounces@lists.squeakfoundation.org> im Auftrag von Eliot Miranda <eliot.miranda@gmail.com><br>
<b>Gesendet:</b> Sonntag, 23. Februar 2020 18:19 Uhr<br>
<b>An:</b> The general-purpose Squeak developers list<br>
<b>Betreff:</b> Re: [squeak-dev] Swap operation for stack machinery?</font>
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<blockquote type="cite">On Feb 23, 2020, at 9:01 AM, Thiede, Christoph <Christoph.Thiede@student.hpi.uni-potsdam.de> wrote:<br>
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<p>Hi all,</p>
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<p>I am curious to know whether the Squeak Context model provides any operation to swap the latest two elements from the stack. Something like:</p>
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<div>doSwap</div>
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<div><span style="white-space:pre"></span> | first second |</div>
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<div><span style="white-space:pre"><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px; white-space:pre"></span></span> first :=
self pop.</div>
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<div><span style="white-space:pre"><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px; white-space:pre"></span></span> second
:= self pop.</div>
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<div><span style="white-space:pre"><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px; white-space:pre"></span></span> self push:
first.</div>
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<div><span style="white-space:pre"><span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols; font-size:16px; white-space:pre"></span></span> self push:
second.</div>
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<p><br>
If it exists, I could not find it yet. If it does not exist, would you see any need to implement it (for both VM & simulation, of course)?</p>
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<p>To me, this appears to be the most performant approach to implement a <a href="http://forum.world.st/Problems-with-caseError-tp5111930p5112251.html" class="OWAAutoLink">
parametrized #caseError:</a>. Something like:</p>
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<div>81 <75> pushConstant: 0</div>
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<div>82 <88> dup</div>
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<div>83 <76> pushConstant: 1</div>
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<div>84 <B6> send: =</div>
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<div>85 <9A> jumpFalse: 89</div>
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<div>86 <87> pop</div>
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<div>87 <22> pushConstant: #one</div>
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<div>88 <96> jumpTo: 97</div>
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<div>89 <77> pushConstant: 2</div>
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<div>90 <B6> send: =</div>
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<div>91 <99> jumpFalse: 94</div>
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<div>92 <21> pushConstant: #two</div>
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<div>93 <91> jumpTo: 97</div>
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<div><b>94 <70> self</b></div>
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<div><b>95 <xx> swap</b></div>
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<div><b>96 <D0> send: caseError:</b></div>
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<div>97 <87> pop</div>
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<div>Otherwise, we would need an extra temporary variable here.</div>
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<div><br>
</div>
BTW there is a horrible hack which avoids the extra temp. Since the stack pointer and stack height are known during code generation then instead of this:
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<div><b>94 <70> self</b></div>
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<div><b>95 <xx> swap</b></div>
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<div><b>96 <D0> send: caseError:</b></div>
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<div>one could emit this sequence:
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<div> dup</div>
<div> push self</div>
<div> pop and store temp: N (where N gets to sp - 1)</div>
<div> send caseError:<br>
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Looking forward to your answers.
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<p>Best,</p>
<p>Christoph</p>
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