[PATCH] D13033: [AArch64/ARM] Emit clrex in the ll/sc-expanded cmpxchg no-store path.

[Ahmed Bougacha via llvm-commits]

ab created this revision.
ab added reviewers: t.p.northover, jmolloy.
ab added a subscriber: llvm-commits.
Herald added subscribers: rengolin, aemerson.

In the comparison failure path of a cmpxchg expansion, the initial
ldrex/ldxr will not be followed by a matching strex/stxr.
On ARM/AArch64, this unnecessarily ties up the execution monitor,
which might have a negative performance impact on some uarchs.

Instead, release the monitor in the failure block.
The clrex instruction was designed for this: use it.

Also see ARMARM v8-A B2.10.2:
"Exclusive access instructions and Shareable memory locations".

http://reviews.llvm.org/D13033

Files:
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/AtomicExpandPass.cpp
  lib/Target/AArch64/AArch64ISelLowering.cpp
  lib/Target/AArch64/AArch64ISelLowering.h
  lib/Target/ARM/ARMISelLowering.cpp
  lib/Target/ARM/ARMISelLowering.h
  test/CodeGen/AArch64/arm64-atomic.ll
  test/CodeGen/AArch64/atomic-ops.ll
  test/CodeGen/ARM/atomic-cmp.ll
  test/CodeGen/ARM/atomic-cmpxchg.ll
  test/CodeGen/ARM/atomic-op.ll
  test/CodeGen/ARM/atomic-ops-v8.ll
  test/CodeGen/ARM/cmpxchg-weak.ll
  test/Transforms/AtomicExpand/ARM/atomic-expansion-v7.ll
  test/Transforms/AtomicExpand/ARM/atomic-expansion-v8.ll
  test/Transforms/AtomicExpand/ARM/cmpxchg-weak.ll

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