<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><br></div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"daniel smith" <daniel.smith@oracle.com><br><b>To: </b>"Remi Forax" <forax@univ-mlv.fr><br><b>Cc: </b>"John Rose" <john.r.rose@oracle.com>, "valhalla-spec-experts" <valhalla-spec-experts@openjdk.java.net><br><b>Sent: </b>Monday, August 21, 2023 9:12:03 PM<br><b>Subject: </b>Re: The last miles<br></blockquote></div><div data-marker="__QUOTED_TEXT__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;">
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<div>On Aug 21, 2023, at 11:39 AM, forax@univ-mlv.fr wrote:</div>
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1) A larval value object is an identity object. This means, in the hand-off<br>
between the <init> method and the caller, the object must be heap allocated:<br>
the caller and the <init> method need an agreed-upon memory location where<br>
state will be set up.<br>
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I can see this being optimized away if the <init> method can be inlined. But if<br>
not (e.g., the constructor logic is sufficiently complex/large), that's a new<br>
cost for value object creation: every 'new' needs a heap allocation. (For<br>
<vnew>, we are able to optimize the return value calling convention without<br>
needing inlining.)<br>
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<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">A
larval value object is a value object with the larval state to "on", it's not an identity object.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">At
the end of the call of <init>, the larval state is set to "off".</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">The
larval bit controls if putfield is allowed or not.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
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<div>I mean it is an "identity object" in the sense that it must live at a canonical, mutable memory location. E.g., you can't scalarize it across calls, you have to pass it by reference. But, agreed, "larval object" and "identity object" are distinct concepts.
It's just that both of them depend on some sort of "identity" capability.</div>
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<div>(Separately, we can dig further into the question of whether you actually need runtime flags to detect this state change, or can leave it to verification. That's my point (5).)</div>
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<div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">In
the interpreter, a larval value object is buffered, so there is an heap allocation.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">But
in JITed code, if everything is inlined</span></div>
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<div>Exactly: "if everything is inlined". My point (1) is that if everything *is not* inlined, there are allocations that <vnew> was able to optimize away.</div></div></blockquote><div><br></div><div>inside <vnew>, yes, but at the end of <vnew> if it goes back into the interpreter, the return value will be buffered.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>I do not think it is obvious if there will be performance regression or not until the new scheme is implemented and tested.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Rémi<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div></div></div></body></html>