[PATCH] D124319: [MC][AArch64] Enable '+v8a' when nothing specified for MCSubtargetInfo

[Tommy Chiang via Phabricator via llvm-commits]

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Since D110065 <https://reviews.llvm.org/D110065>, the 'R' profile support is added to LLVM. It turns the
`generic` cpu into the intersection of v8-a and v8-r. However, this
makes some backward compatibility problems. The original patch makes
the clang driver implicitly pass -march=armv8-a when only the triple
is specified. Since it only applies to clang, other tools like
llvm-objdump still faces the backward compatibility problem.

This patch applies the same idea to MC related tools by enabling '+v8a'
feature when nothing is specified (bot CPU and FS are empty) for
MCSubtargetInfo creation.

This patch should fix PR53956.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124319

Files:
  llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
  llvm/test/MC/AArch64/arm64-branch-encoding.s
  llvm/test/MC/AArch64/arm64-system-encoding.s
  llvm/test/MC/AArch64/basic-a64-instructions.s
  llvm/test/MC/Disassembler/AArch64/arm64-branch.txt
  llvm/test/MC/Disassembler/AArch64/basic-a64-instructions.txt

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