@_noLocks doesn't work with Builtin.atomicload_{}

[jcavar]

Description

The new Atomic type cannot be used with @_noLocks since a simple usage reports a violation. It seems that the issue is in the implementation of Atomic load and the use Builtin.atomicload_{} family of functions.

A simplified code sample is available below. Required settings:

swiftSettings: [
    .unsafeFlags(["-disable-availability-checking"]),
    .enableExperimentalFeature("StaticExclusiveOnly"),
    .enableExperimentalFeature("RawLayout"),
    .enableExperimentalFeature("BuiltinModule")
]

Reproduction

import Builtin

public struct MyAtomic: ~Copyable {
  var rawAddress: Builtin.RawPointer {
    Builtin.unprotectedAddressOfBorrow(self)
  }
}

extension MyAtomic {
  @_noLocks
  public func load(ordering: AtomicLoadOrdering) -> Int {
    let result = Builtin.atomicload_monotonic_Int64(rawAddress) // error: this code pattern can cause locking
    return 1
  }
}

Expected behavior

Atomic load doesn't cause locking and performance annotation doesn't report violation.

Environment

Apple Swift version 6.0-dev (LLVM 57177aa1b91540b, Swift 3889ede)
Target: arm64-apple-macosx14.0

Additional information

cc @eeckstein @Azoy

[Azoy]

Looks like we classify atomic instructions as locking:

case BuiltinValueKind::Fence:
case BuiltinValueKind::CmpXChg:
case BuiltinValueKind::AtomicLoad:
case BuiltinValueKind::AtomicStore:
case BuiltinValueKind::AtomicRMW:
  return RuntimeEffect::Locking;

[jcavar]

Is there a reason for that? Can we mark them as NoEffect?

[jcavar]

Hey @Azoy and @eeckstein, just wanted to check in and see if there have been any updates on this issue?

[eeckstein]

Let's just fix this: #75615

[jcavar]

Thank you! Works great!