[all-commits] [llvm/llvm-project] 79fec2: [AtomicExpand][RISCV] Call shouldExpandAtomicRMWIn...

[Craig Topper via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 79fec2f8ba8ea0b0b1c2f13fb6355cb395e1d3af
      https://github.com/llvm/llvm-project/commit/79fec2f8ba8ea0b0b1c2f13fb6355cb395e1d3af
  Author: Craig Topper <craig.topper at sifive.com>
  Date:   2024-02-07 (Wed, 07 Feb 2024)

  Changed paths:
    M llvm/lib/CodeGen/AtomicExpandPass.cpp

  Log Message:
  -----------
  [AtomicExpand][RISCV] Call shouldExpandAtomicRMWInIR before widenPartwordAtomicRMW (#80947)

This gives the target a chance to keep an atomicrmw op that is smaller
than the minimum cmpxchg size. This is needed to support the Zabha
extension for RISC-V which provides i8/i16 atomicrmw operations, but
does not provide an i8/i16 cmpxchg or LR/SC instructions.

This moves the widening until after the target requests
LLSC/CmpXChg/MaskedIntrinsic expansion. Once we widen, we call
shouldExpandAtomicRMWInIR again to give the target another chance to
make a decision about the widened operation.

I considered making the targets return AtomicExpansionKind::Expand or a
new expansion kind for And/Or/Xor, but that required the targets to
special case And/Or/Xor which they weren't currently doing.