<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div dir="ltr"><br></div><div dir="ltr"><br><blockquote type="cite">On Feb 23, 2020, at 9:01 AM, Thiede, Christoph <Christoph.Thiede@student.hpi.uni-potsdam.de> wrote:<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
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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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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></div></div></div></blockquote><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:<div><div dir="ltr"><div id="divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif;"><blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div dir="ltr" style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;"><div><b><br></b></div><div><b>94 <70> self</b></div><p></p></div><div dir="ltr" style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;"><p></p><div><b>95 <xx> swap</b></div><p></p></div><div dir="ltr" style="font-size: 12pt; font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;"><p></p><div><b>96 <D0> send: caseError:</b></div><div><b><br></b></div></div></blockquote></div></div></div><div>one could emit this sequence:<div><br></div><div> dup</div><div> push self</div><div> pop and store temp: N (where N gets to sp - 1)</div><div> send caseError:<br><div><br><blockquote type="cite"><div dir="ltr"><div id="divtagdefaultwrapper" style="font-size:12pt;color:#000000;font-family:Calibri,Helvetica,sans-serif;" dir="ltr"><div dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, EmojiFont, "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
Looking forward to your answers.
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<p>Best,</p>
<p>Christoph</p>
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