<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hi Ashutosh,</div><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 22, 2017, at 1:57 AM, Nema, Ashutosh via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Hi,<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">This is a proposal about epilog loop vectorization.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Currently Loop Vectorizer inserts an epilogue loop for handling loops that don’t have known iteration counts.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">The Loop Vectorizer supports loops with an unknown trip count, unknown trip count may not be a multiple of the vector width, and the vectorizer has to execute the last few iterations as scalar code. It keeps a scalar copy of the loop for the remaining iterations.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Loop with the large width has a high possibility of executing many scalar iterations.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">i.e. i8 data type with 256bits target register can vectorize with vector width 32, with that maximum trip count possibility for scalar(epilog) loop is 31, which is significant & worth vectorizing.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Large vector factor has following challenges:<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -0.25in;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif;" class=""><span class="">1)<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span></span><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Possibility of remainder iteration is substantial.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -0.25in;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif;" class=""><span class="">2)<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span></span><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Actual trip count at runtime is substantial but not meeting minimum trip count to execute vector loop.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">These challenges can be addressed by mask instructions, but these instructions are limited and may not be available to all targets.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">By epilog vectorization our aim to vectorize epilog loop where original loop is vectorized with large vector factor and has a high possibility of executing scalar iterations.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">This require following changes:<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -0.25in;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif;" class=""><span class="">1)<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span></span><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Costing: Preserve all profitable vector factor.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -0.25in;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif;" class=""><span class="">2)<span style="font-style: normal; font-variant-caps: normal; font-weight: normal; font-size: 7pt; line-height: normal; font-family: 'Times New Roman';" class=""> <span class="Apple-converted-space"> </span></span></span></span><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Transform: Create an additional vector loop with next profitable vector factor.</span></div></div></div></blockquote><div><br class=""></div><div>Is this something that you propose to be on by default for wide VPU architectures without masking support? I.e. how widely is this applicable? If not then perhaps a better strategy would be to just annotate the remainder loop with some metadata to limit the vectorization factor and just rerun the vectorizer.</div><div><br class=""></div><div>Adam</div><br class=""><blockquote type="cite" class=""><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: -0.25in;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Please refer attached file (BlockLayout.png) for the details about transformed block layout.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Patch is available at:<span class="Apple-converted-space"> </span><a href="https://reviews.llvm.org/D30247" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">https://reviews.llvm.org/D30247</a><o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Regards,<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Lucida Sans Unicode', sans-serif; background-color: white;" class="">Ashutosh<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><span id="cid:770D11B0-E822-4799-8A56-411EB81EBD02@apple.com"><BlockLayout.png></span><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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