[PATCH] D140297: [AArch64] Add RSHRN and RSHRN2 patterns

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: SjoerdMeijer, bipmis, samtebbs, fhahn.
Herald added subscribers: hiraditya, kristof.beyls.
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This adds some tablegen patterns for RSHRN, which performs a rounding shift with narrow. This is similar to the existing SHRN patterns with an extra addition to perform the rounding, that adds `1<<(shift-1)` before the right shift. Because the round immediate and the shift amount are tied, it goes via a ComplexPattern that uses a SelectRoundingVLShr method to perform the selection checks.

aarch64_neon_rshrn are expanded into the sequence of equivalent instructions (`trunc(shr(add(x, 1<<(sht-1)), sht))`) so that they can be converted back into RSHRN. Which also allows us to match raddhn through the adjusted patterns that previously used aarch64_neon_rshrn.


https://reviews.llvm.org/D140297

Files:
  llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.td
  llvm/test/CodeGen/AArch64/neon-rshrn.ll

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