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Thanks for your reply. This direction looked sensible, and I wanted to check if we weren't missing anything.</div>
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Cheers,</div>
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Sjoerd.<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Philip Reames <listmail@philipreames.com><br>
<b>Sent:</b> 09 August 2019 23:47<br>
<b>To:</b> Sjoerd Meijer <Sjoerd.Meijer@arm.com>; cfe-dev@lists.llvm.org <cfe-dev@lists.llvm.org><br>
<b>Cc:</b> nd <nd@arm.com><br>
<b>Subject:</b> Re: [cfe-dev] Behaviour of loop pragmas and transformation options</font>
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<div class="x_moz-cite-prefix">On 8/7/19 12:25 AM, Sjoerd Meijer via cfe-dev wrote:<br>
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<span>We have recently added support for a new loop pragma 'vectorize_predicate' [1].<br>
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<div>During review of the LLVM part that does the actual transformation [2], the<br>
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<div>question was raised if 'vectorize_predicate' should imply 'vectorize(enable)'.<br>
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<div>I agree that this is indeed what users would most likely expect and so I<br>
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<div>created a patch for that [3].<br>
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<div>During review of [3], Florian mentioned bug report [4] supporting the case that<br>
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<div>users indeed expect that more specific pragmas such as e.g. vectorize_width(4)<br>
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<div>should imply vectorize(enable), but this is currently not the case. But our<br>
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<div>docs for example mention: "The following example implicitly enables<br>
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<div>vectorization and interleaving by specifying a vector width and interleaving<br>
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<div>count", and so we have an inconsistency in the docs and implementation. But as<br>
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<div>I have e.g. no clue what the behaviour could be of "vectorize(disable)<br>
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<div>vectorize_predicate(enable)", I would say the docs are right and the<br>
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<div>implementation is wrong.<br>
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<div>Michael mentioned that the situation with for example loop unroll pragmas<br>
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<div>'unroll(enable) unroll_count(4)' is not very different. Pragma 'unroll_count'<br>
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<div>also does not set 'llvm.loop.unroll.enable', but it is handled by the<br>
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<div>LoopUnroll pass itself and so we end up with checks like this:<br>
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<div> bool ExplicitUnroll = PragmaCount > 0 || PragmaFullUnroll ||<br>
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<div> PragmaEnableUnroll || UserUnrollCount;<br>
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<div>And again, this is very similar to 'vectorize_width', and we have different<br>
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<div>checks to see if vectorization is enabled.<br>
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<div>Because of the many inconsistencies, we came to the conclusion in [3] that we<br>
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<div>don't know how know how to (best) implement that setting an transformation<br>
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<div>option implies setting the transformation.<br>
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<div>My proposal would be that the transformation options imply the transformations<br>
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<div>by setting the enable flag of that transformation. Thus, vectorize options<br>
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<div>vectorize_width, vectorize_predicate, etc., set vectorize(enable), and unroll<br>
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<div>option unroll count set unroll(enable).<br>
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I second this. The complexities of which pragmas enable which transforms should be handled entirely in Clang, with Clang responsible for emitting a consistent set of metadata flags to LLVM.
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<div>Any thoughts on this welcome.<br>
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<div>[1] <a class="x_moz-txt-link-freetext" href="https://reviews.llvm.org/rL366989">
https://reviews.llvm.org/rL366989</a><br>
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<div>[2] <a class="x_moz-txt-link-freetext" href="https://reviews.llvm.org/D65197">
https://reviews.llvm.org/D65197</a><br>
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<div>[3] <a class="x_moz-txt-link-freetext" href="https://reviews.llvm.org/D65776">
https://reviews.llvm.org/D65776</a><br>
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<span>[4] <a href="https://bugs.llvm.org/show_bug.cgi?id=27643" id="LPlnk126071">
https://bugs.llvm.org/show_bug.cgi?id=27643</a></span><br>
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