[all-commits] [llvm/llvm-project] 843c61: [AArch64] Fix i128 cmpxchg using ldxp/stxp.

[Eli Friedman via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 843c61405881acdac1727c3a1ca4f36156611753
      https://github.com/llvm/llvm-project/commit/843c61405881acdac1727c3a1ca4f36156611753
  Author: Eli Friedman <efriedma at quicinc.com>
  Date:   2021-07-20 (Tue, 20 Jul 2021)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Target/AArch64/AArch64InstrAtomics.td
    M llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
    M llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic-128.ll
    M llvm/test/CodeGen/AArch64/GlobalISel/legalize-cmpxchg-128.mir
    M llvm/test/CodeGen/AArch64/arm64-atomic-128.ll
    M llvm/test/CodeGen/AArch64/atomicrmw-O0.ll

  Log Message:
  -----------
  [AArch64] Fix i128 cmpxchg using ldxp/stxp.

Basically two parts to this fix:

1. Stop using AtomicExpand to expand cmpxchg i128
2. Fix AArch64ExpandPseudoInsts to use a correct expansion.

>From ARM architecture reference:

To atomically load two 64-bit quantities, perform a Load-Exclusive
pair/Store-Exclusive pair sequence of reading and writing the same value
for which the Store-Exclusive pair succeeds, and use the read values
from the Load-Exclusive pair.

Fixes https://bugs.llvm.org/show_bug.cgi?id=51102

Differential Revision: https://reviews.llvm.org/D106039