[PATCH] D130192: [RISCV] Avoid redundant branch-to-branch when expanding cmpxchg

[Alex Bradbury via Phabricator via llvm-commits]

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If the success value of a cmpxchg is used in a branch, the expanded cmpxchg sequence ends up with a redundant branch-to-branch (as the backend atomics expansion happens as late as possible, passes to optimise such cases have already run). This patch identifies this case and avoid it when expanding the cmpxchg.

Note that a similar optimisation is possible for a BEQ on the cmpxchg success value. As it's hard to imagine a case where real-world code may do that, this patch doens't handle that case.


https://reviews.llvm.org/D130192

Files:
  llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp
  llvm/test/CodeGen/RISCV/atomic-cmpxchg-branch-on-result.ll

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