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<div class="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>
</span>
<div>During review of the LLVM part that does the actual
transformation [2], the<br>
</div>
<div>question was raised if 'vectorize_predicate' should imply
'vectorize(enable)'.<br>
</div>
<div>I agree that this is indeed what users would most likely
expect and so I<br>
</div>
<div>created a patch for that [3].<br>
</div>
<div><br>
</div>
<div>During review of [3], Florian mentioned bug report [4]
supporting the case that<br>
</div>
<div>users indeed expect that more specific pragmas such as e.g.
vectorize_width(4)<br>
</div>
<div>should imply vectorize(enable), but this is currently not
the case. But our<br>
</div>
<div>docs for example mention: "The following example implicitly
enables<br>
</div>
<div>vectorization and interleaving by specifying a vector width
and interleaving<br>
</div>
<div>count", and so we have an inconsistency in the docs and
implementation. But as<br>
</div>
<div>I have e.g. no clue what the behaviour could be of
"vectorize(disable)<br>
</div>
<div>vectorize_predicate(enable)", I would say the docs are
right and the<br>
</div>
<div>implementation is wrong.<br>
</div>
<div><br>
</div>
<div>Michael mentioned that the situation with for example loop
unroll pragmas<br>
</div>
<div>'unroll(enable) unroll_count(4)' is not very different.
Pragma 'unroll_count'<br>
</div>
<div>also does not set 'llvm.loop.unroll.enable', but it is
handled by the<br>
</div>
<div>LoopUnroll pass itself and so we end up with checks like
this:<br>
</div>
<div><br>
</div>
<div> bool ExplicitUnroll = PragmaCount > 0 ||
PragmaFullUnroll ||<br>
</div>
<div> PragmaEnableUnroll ||
UserUnrollCount;<br>
</div>
<div><br>
</div>
<div>And again, this is very similar to 'vectorize_width', and
we have different<br>
</div>
<div>checks to see if vectorization is enabled.<br>
</div>
<div><br>
</div>
<div>Because of the many inconsistencies, we came to the
conclusion in [3] that we<br>
</div>
<div>don't know how know how to (best) implement that setting an
transformation<br>
</div>
<div>option implies setting the transformation.<br>
</div>
<div><br>
</div>
<div>My proposal would be that the transformation options imply
the transformations<br>
</div>
<div>by setting the enable flag of that transformation. Thus,
vectorize options<br>
</div>
<div>vectorize_width, vectorize_predicate, etc., set
vectorize(enable), and unroll<br>
</div>
<div>option unroll count set unroll(enable).<br>
</div>
</div>
</blockquote>
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. <br>
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cite="mid:VI1PR08MB3341D4A8796389887BF0BFCFFCD40@VI1PR08MB3341.eurprd08.prod.outlook.com">
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<div><br>
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<div>Any thoughts on this welcome.<br>
</div>
<div><br>
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<div><br>
</div>
<div>[1] <a class="moz-txt-link-freetext" href="https://reviews.llvm.org/rL366989">https://reviews.llvm.org/rL366989</a><br>
</div>
<div>[2] <a class="moz-txt-link-freetext" href="https://reviews.llvm.org/D65197">https://reviews.llvm.org/D65197</a><br>
</div>
<div>[3] <a class="moz-txt-link-freetext" href="https://reviews.llvm.org/D65776">https://reviews.llvm.org/D65776</a><br>
</div>
<span>[4] <a href="https://bugs.llvm.org/show_bug.cgi?id=27643"
id="LPlnk126071" moz-do-not-send="true">
https://bugs.llvm.org/show_bug.cgi?id=27643</a></span><br>
</div>
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