<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<br>
<div class="moz-cite-prefix">On 06/21/2018 01:07 PM, Jon
Chesterfield via llvm-dev wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAOUYtQBiB_6YL_pTPc-sE7NTg_skhQX+J2geEOFoX8ZnDVA-uw@mail.gmail.com">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<div dir="ltr">Hi,
<div><br>
</div>
<div>Hexagon has a MIR pass for detecting loops that map onto
hardware support. I think a similar approach would be viable
for my target but am put off by the complexity of determining
whether a given loop is legal to transform.</div>
</div>
</blockquote>
<br>
I think that it is easier to do this legality checking at the IR
level (where we can take advantage of the ScalarEvolution analysis).
This is what PowerPC does (see lib/Target/PowerPC/PPCCTRLoops.cpp).
I recommend that you take this approach if possible.<br>
<br>
-Hal<br>
<br>
<blockquote type="cite"
cite="mid:CAOUYtQBiB_6YL_pTPc-sE7NTg_skhQX+J2geEOFoX8ZnDVA-uw@mail.gmail.com">
<div dir="ltr">
<div><br>
</div>
<div>Instead, I would like to pass the responsibility for
determining legality onto the C programmer who is assumed
sufficiently familiar with the architecture.</div>
<div><br>
</div>
<div>I think this would require a pair of intrinsics to denote
the start and end of the loop. Is there a reasonable way to
model this in llvm?</div>
<div><br>
</div>
<div>If not, would anyone suggest a compiler programmer
friendly, even if application programmer hostile, way to
target a loop instruction with many constraints on validity.</div>
<div><br>
</div>
<div>Thanks!</div>
<div><br>
</div>
<div>Jon</div>
</div>
<!--'"--><br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
LLVM Developers mailing list
<a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>
<a class="moz-txt-link-freetext" href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
</body>
</html>