[PATCH] D114542: [CodeGen][SVE] Use whilelo instruction when lowering @llvm.get.active.lane.mask

[David Sherwood via Phabricator via llvm-commits]

david-arm created this revision.
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In most common cases the @llvm.get.active.lane.mask intrinsic maps directly
to the SVE whilelo instruction, which already takes overflow into account.
However, currently in SelectionDAGBuilder::visitIntrinsicCall we always lower
this immediately to a generic sequence of instructions that explicitly
take overflow into account. This makes it very difficult to then later
transform back into a single whilelo instruction. Therefore, this patch
introduces a new TLI function called lowerGetActiveLaneMask that asks if
we should lower/expand this to a sequence of generic ISD nodes, or instead
just leave it as an intrinsic for the target to lower.

You can see the significant improvement in code quality for some of the
tests in this file:

  CodeGen/AArch64/active_lane_mask.ll


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114542

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.h
  llvm/test/CodeGen/AArch64/active_lane_mask.ll

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