[all-commits] [llvm/llvm-project] b1b108: [ARM] Add target feature to force 32-bit atomics

[Nikita Popov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b1b1086973d5be26f127540852ace59c5119e90a
      https://github.com/llvm/llvm-project/commit/b1b1086973d5be26f127540852ace59c5119e90a
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2022-07-27 (Wed, 27 Jul 2022)

  Changed paths:
    M llvm/lib/Target/ARM/ARM.td
    M llvm/lib/Target/ARM/ARMISelLowering.cpp
    A llvm/test/CodeGen/ARM/thumbv6m-atomic32.ll

  Log Message:
  -----------
  [ARM] Add target feature to force 32-bit atomics

This adds a +atomic-32 target feature, which instructs LLVM to assume
that lock-free 32-bit atomics are available for this target, even
if they usually wouldn't be.

If only atomic loads/stores are used, then this won't emit libcalls.
If atomic CAS is used, then the user is responsible for providing
any necessary __sync implementations (e.g. by masking interrupts
for single-core privileged use cases).

See https://reviews.llvm.org/D120026#3674333 for context on this
change. The tl;dr is that the thumbv6m target in Rust has
historically made atomic load/store only available, which is
incompatible with the change from D120026, which switched these to
use libatomic.

Differential Revision: https://reviews.llvm.org/D130480