[PATCH] D95139: [SVE][LoopVectorize] Add support for extracting the last lane of a scalable vector

[David Sherwood via Phabricator via llvm-commits]

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There are certain loops like this below:

  for (int i = 0; i < n; i++) {
    a[i] = b[i] + 1;
    *inv = a[i];
  }

that can only be vectorised if we are able to extract the last lane of the
vectorised form of 'a[i]'. For fixed width vectors this already works since
we know at compile time what the final lane is, however for scalable vectors
this is a different story. This patch adds support for extracting the last
lane from a scalable vector using a runtime determined lane value. I have
added support to VPIteration for non-constant lanes that still permits the
caching of values. Whilst doing this work I couldn't find any explicit tests
for extracting the last lane values of fixed width vectors so I added tests
for both scalable and fixed width vectors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95139

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
  llvm/lib/Transforms/Vectorize/VPlan.h
  llvm/test/Transforms/LoopVectorize/AArch64/neon-extract-last-veclane.ll
  llvm/test/Transforms/LoopVectorize/AArch64/sve-extract-last-veclane.ll

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