<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
<div class="">Hi Vedant,</div>
<div class=""> Responses inline...</div>
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On May 8, 2017, at 1:22 PM, Vedant Kumar <<a href="mailto:vsk@apple.com" class="">vsk@apple.com</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">
<br class="Apple-interchange-newline">
On May 8, 2017, at 10:49 AM, Sanjoy Das <<a href="mailto:sanjoy@playingwithpointers.com" class="">sanjoy@playingwithpointers.com</a>> wrote:<br class="">
<br class="">
Hi Daniel,<br class="">
<br class="">
[+CC Mehdi, Vedant for the auto upgrade issue]<br class="">
<br class="">
On Mon, May 8, 2017 at 7:54 AM, Daniel Neilson via llvm-dev<br class="">
<<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:<br class="">
<blockquote type="cite" class="">**Method**<br class="">
<br class="">
Clearly we are going to have to teach LLVM about unordered memory<br class="">
intrinsics. There are, as I can see it, a couple of ways to accomplish this.<br class="">
I’d like your opinions on which are preferable, or if you can think of any<br class="">
other options. In no particular order…<br class="">
<br class="">
Option 1)<br class="">
Introduce a new unordered/element-atomic version of each of the memory<br class="">
intrinsics.<br class="">
Ex: @llvm.memcpy_element_atomic — work was already started to introduce<br class="">
this one in D27133, but could be backed out and restarted.<br class="">
</blockquote>
</blockquote>
<br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">I'm
curious about this -- do you know why the decision was made in D27133 to go with a new intrinsic, instead of extending the existing one? Would the same rationale apply here?</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
</div>
</blockquote>
<div><br class="">
</div>
<div>The rationale as I understand it basically boils down to minimizing risk — make the changes with the introduction of a new intrinsic that’ll be invisible in practice to anyone except Java, see how that looks/feels, and then extend the existing one (& remove
the added one) once it looks like it’ll work. I have no problem with continuing that line, but I do prefer to move away from the separate intrinsic after the thing has been proven out.</div>
<br class="">
<blockquote type="cite" class="">
<div class="">
<blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">
<br class="">
<blockquote type="cite" class="">Cons:<br class="">
* Breaks backward compatibility of the IR — is there a mechanism for<br class="">
migrating old IR into a new IR version when loading the IR into LLVM?<br class="">
</blockquote>
<br class="">
I think the migration here will be fairly straightforward -- you can<br class="">
just auto-upgrade old calls to memcpy to pass in 0 for the isordered<br class="">
argument. But I've CC'd Mehdi and Vedant to help shed some light on<br class="">
this.<br class="">
</blockquote>
<br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">LLVM
has one test which for backwards-compatibility with old versions of the memcpy intrinsic, which provides limited coverage (standardCIntrinsic.3.2.ll).</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Whichever
option you choose, it would be helpful to add uses of the new intrinsic to test/Bitcode/compatibility.ll. If you choose Option 2, it would also help to copy these uses into the 4.0 bitcode compatibility test (with "is_unordered" dropped), and to re-generate
the bitcode for the test. I can help out with this if you'd like.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
</div>
</blockquote>
<div><br class="">
</div>
<div>Will do, and I’ll definitely reach out for assistance with the bitcode compatibility test when the time arrives. Thanks!</div>
<div><br class="">
</div>
<div>-Daniel</div>
<div><br class="">
</div>
<div>
<div>---</div>
<div>Daniel Neilson, Ph.D.</div>
<div>Azul Systems</div>
<div class=""><br class="">
</div>
<br class="Apple-interchange-newline">
</div>
</div>
</body>
</html>