[PATCH] D109432: [LoopVectorize] Permit fixed-width epilogue loops for scalable vector bodies

[Bardia Mahjour via Phabricator via llvm-commits]

bmahjour added a comment.

Different plans may have different recipes, so if we don't find a single plan that supports both the main VF and the epilogue VF, I worry we may get unintended codegen. Furthermore, what guarantees that a vplan with a fixed-width conversion from the scalable VF actually exists? Would it be possible to build scalable plans that include the corresponding fixed width (and some lower powers of 2) VFs?



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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:6262
 
-  if (!isEpilogueVectorizationProfitable(MainLoopVF))
+  ElementCount EpilogueVF = MainLoopVF;
+  if (EpilogueVF.isScalable()) {
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"EpilogueVF" is confusing here, since the rest of the logic expects main-loop VF. Suggest renaming to "KnownMainLoopVF" or "FixedMainLoopVF" or "FixedWidthMainLoopVF".


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Comment at: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:6266
+        dbgs() << "LEV: Epilogue vectorization using scalable vectors not "
+                  "yet supported. Converting to fixed-width instead\n");
+    EpilogueVF = ElementCount::getFixed(EpilogueVF.getKnownMinValue());
----------------
include the fixed-width value in the debug message?


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https://reviews.llvm.org/D109432