[PATCH] D84395: [AArch64] Fix a machine verifier ICE when using __builtin_return_address with return address sign and authentication

[Momchil Velikov via Phabricator via llvm-commits]

chill created this revision.
chill added reviewers: MatzeB, t.p.northover.
Herald added subscribers: llvm-commits, hiraditya, kristof.beyls.
Herald added a project: LLVM.

When using PAuth instructions in the NOP-space, the compiler can emit an
 `AUTIxSP` instruction in the function epilogue.

In a certain test case, using `__builtin_return_address`, the compiler causes
the machine verifier to exit with an error after turning

  %0 = COPY LR
  x0 = COPY killed %0

into

  x0 = COPY killed LR

and the backend later emitting

  x0 = COPY killed LR
  AUTIASP implicit def LR, implicit LR

This is obviously incorrect since `LR` is live beyond the `COPY` instruction.

The issue is that lifetime of the return address is not tracked properly. The
backend relies on the callee-saved registers mechanism to ensure `LR` is
restored before used for return. For the return instruction that's handled with
a little hack to appease the verifier.

This patch employs the same hack for `AUTIxSP`, marking the implicit `LR`
operand as `undef`.


https://reviews.llvm.org/D84395

Files:
  llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
  llvm/test/CodeGen/AArch64/builtin-return-address-autisap.ll
  llvm/test/CodeGen/AArch64/machine-outliner-retaddr-sign-sp-mod.mir
  llvm/test/CodeGen/MIR/AArch64/return-address-signing.mir

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