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<div>One typo fixed inline<br>
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Thanks for bringing this up here. We have discussed this already on <a href="https://reviews.llvm.org/D89031" id="LPlnk844168">
https://reviews.llvm.org/D89031</a> and a bit offline, and it would be good to get some other opinions on this too.</div>
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What we achieve with this extension is that we can toggle fixed/scalable vectorisation. The proposal is to add this property to vectorize_width, because it kind of defines the VectorType which consists of the elementcount and the scalable/fixed part, which
sounds reasonable. However, there are other loop pragmas that (implicitly) enable vectorisation:</div>
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#pragma clang loop interleave_count(some-number)</div>
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or</div>
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#pragma clang loop vectorize_predicate(enable)</div>
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for which you may want to toggle fixed|scalable vectorisation. If this is correct, then I think the current proposal/implementation is incomplete and/or inconsistent.</div>
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I think your own suggestion was to introduce a vectorization_style(enable|disable) at some point, </div>
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I meant vectorization_style(fixed|scalable) <br>
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but my proposal would be to use that instead of adjusting vectorize_width as that would address the issue incompleteness/inconsistency issue. Besides this, but more subjective, I don't see all the new combinations of vectorize_width() as making things clearer:<br>
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vectorize_width(VF)</div>
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vectorize_width(VF, fixed|scalable)<br>
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vectorize_width(fixed|scalable)<br>
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Probably the implementation of adding vectorization_style(enable|disable) is easier and less contentious than adjusting an existing one, so all together I don't see why the approach of adjusting vectorize_wdith would be preferred. But I might be wrong, might
be missing something, so welcome other views on this.<br>
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Cheers,</div>
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Sjoerd.<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> cfe-dev <cfe-dev-bounces@lists.llvm.org> on behalf of David Sherwood via cfe-dev <cfe-dev@lists.llvm.org><br>
<b>Sent:</b> 24 November 2020 09:04<br>
<b>To:</b> cfe-dev@lists.llvm.org <cfe-dev@lists.llvm.org><br>
<b>Subject:</b> [cfe-dev] Proposed changes to vectorize_width #pragma</font>
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Hi,</p>
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At the moment the vectorize_width(X) #pragma is used to provide hints to LLVM</p>
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about which vectorisation factor to use. The unsigned argument ‘X’ used to match</p>
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the NumElements property in the VectorType class, however VectorType is now</p>
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defined in terms of a ElementCount class.</p>
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I’d like to propose an extension to the vectorize_width #pragma that now takes</p>
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an optional second parameter of ‘fixed’ or ‘scalable’ that matches up with</p>
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ElementCount. When not specified the default value would be ‘fixed’. A few</p>
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examples of how this would look like are shown below:</p>
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// Vectorize the loop with <4 x eltty></p>
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#pragma clang loop vectorize_width(4)</p>
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#pragma clang loop vectorize_width(4, fixed)</p>
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// Vectorize the loop with <vscale x 4 x eltty></p>
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#pragma clang loop vectorize_width(4, scalable)</p>
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As a further extension I’d also like to permit vectorize_width(fixed|scalable) to</p>
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allow users to hint at the type of vector used without specifying the</p>
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vectorisation factor. Examples of this would be:</p>
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// Vectorize the loop with <N x eltty> for a profitable N</p>
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#pragma clang loop vectorize_width(fixed)</p>
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// Vectorize the loop with <vscale x N x eltty> for a profitable N</p>
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#pragma clang loop vectorize_width(scalable)</p>
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Any thoughts you have would be much appreciated!</p>
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Kind Regards,</p>
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David Sherwood.</p>
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