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<p class="MsoNormal">Hi Roger,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks for the suggestion. With regards to possible use cases of a vectorize_style(any)<o:p></o:p></p>
<p class="MsoNormal">pragma my thoughts are:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">1. Any existing tests that currently use vectorize_width(#number) were presumably<o:p></o:p></p>
<p class="MsoNormal">written with fixed width vectorisation in mind. So it makes sense in those cases<o:p></o:p></p>
<p class="MsoNormal">for the default to be fixed width. If the user wants to go back and fix them to explicitly<o:p></o:p></p>
<p class="MsoNormal">use scalable vectorisation they can just add vectorize_width(#number, scalable). We<o:p></o:p></p>
<p class="MsoNormal">feel that specifying the numeric part of the vectorisation factor without also considering<o:p></o:p></p>
<p class="MsoNormal">if the factor is fixed-length or scalable is not a realistic/real world use case. I imagine<o:p></o:p></p>
<p class="MsoNormal">that best results will be obtained by letting the vectoriser choose the best pair, i.e.<o:p></o:p></p>
<p class="MsoNormal">vectorize_width(4, fixed) or vectorize_width(8, scalable).<o:p></o:p></p>
<p class="MsoNormal">2. However, if the user wants the compiler to choose the best option (fixed or scalable)<o:p></o:p></p>
<p class="MsoNormal">then we already have a route for that with vectorize(enable). Similarly when compiling<o:p></o:p></p>
<p class="MsoNormal">at -O2 or above the compiler will choose the most profitable option.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Kind Regards,<o:p></o:p></p>
<p class="MsoNormal">David.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Roger Ferrer Ibáñez <rofirrim@gmail.com>
<br>
<b>Sent:</b> 30 November 2020 13:34<br>
<b>To:</b> David Sherwood <David.Sherwood@arm.com><br>
<b>Cc:</b> cfe-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [cfe-dev] Proposed changes to vectorize_width #pragma<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi David,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Your proposal looks sensible to me. I understand that for reasons of evolution of the pragma, you chose to give it `fixed` semantics if no explicit mark of vectorisation style appears, right?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is this something in the future we'd want to relax? This way the target could also pick the best vectorization style (borrowing Sjoerd's terminology here).
<o:p></o:p></p>
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<p class="MsoNormal">Perhaps we could define a `vectorize_style(any)` as well. That would be the one used if no explicit `vectorize_style` is specified.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">As a further extension I’d also like to permit vectorize_width(fixed|scalable) to<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">allow users to hint at the type of vector used without specifying the<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">vectorisation factor. Examples of this would be:<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="gmail-m-5052617891530397558msoplaintext"> // Vectorize the loop with <N x eltty> for a profitable N<o:p></o:p></p>
<p class="gmail-m-5052617891530397558msoplaintext"> #pragma clang loop vectorize_width(fixed)<o:p></o:p></p>
<p class="gmail-m-5052617891530397558msoplaintext"> // Vectorize the loop with <vscale x N x eltty> for a profitable N<o:p></o:p></p>
<p class="gmail-m-5052617891530397558msoplaintext"> #pragma clang loop vectorize_width(scalable)<o:p></o:p></p>
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<p class="MsoNormal">In those cases, I imagine `vectorize_style` could be enough and we avoid having a `vectorize_width` that doesn't actually tell us the width (or the factor of the actual width, for scalables). But this falls in the "aesthetics" category,
I think.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Kind regards,<o:p></o:p></p>
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