[PATCH] D101990: [AArch64][SVE] Improve SVE codegen for fixed length BITCAST

[Bradley Smith via Phabricator via llvm-commits]

bsmith created this revision.
bsmith added reviewers: paulwalker-arm, peterwaller-arm, joechrisellis, david-arm.
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Expanding a fixed length operation involves wrapping the operation in an
insert/extract subvector pair, as such, when this is done to bitcast we
end up with an extract_subvector of a bitcast. DAGCombine tries to
convert this into a bitcast of an extract_subvector which restores the
initial fixed length bitcast, causing an infinite loop of legalization.

As part of this patch, we must make sure the above DAGCombine does not
trigger after legalization if the created bitcast would not be legal.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101990

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.h
  llvm/test/CodeGen/AArch64/sve-fixed-length-bitcast.ll

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