Noncopyable deinit causes compiler crash or miscompile with tsan

[WFT]

Description

This copied from this forum post: https://forums.swift.org/t/noncopyable-type-has-deinit-called-before-init/72152

I have a test case where a noncopyable struct’s deinit is called twice, leading to memory corruption. This only happens when compiled with thread sanitizer.

On 5.10 this causes a miscompile on 6.0 nightly forum replies say that it crashes (I haven’t tried).

Reproduction

// Run this with swiftc -sanitize=thread test.swift && ./test
import Accelerate

struct Testable: ~Copyable {
    var foo = 999
    init() { print("Initing...") }
    func honk() {
        print(foo)
    }
    deinit { print("Deinit!") }
}

struct Thing: ~Copyable {
    var buffer: UnsafeMutableBufferPointer<Float>
    var t: Testable

    init() {
        buffer = .allocate(capacity: 100)
        vDSP.clear(&buffer)
        t = Testable()
    }

    func test() {
        t.honk()
    }

    deinit {
        buffer.deallocate()
    }
}


Thing().test()

Stack dump

error: compile command failed due to signal 6 (use -v to see invocation)
Found a write classified as a liveness use?!
Use:   %18 = builtin "tsanInoutAccess"(%17 : $*UnsafeMutableBufferPointer<Float>) : $()
standard failure
UNREACHABLE executed at /Users/ec2-user/jenkins/workspace/oss-swift-6.0-package-macos/swift/lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp:2730!
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the crash backtrace.

Expected behavior

I expected it to print this:

Initing...
999
Deinit!

On swift 5.10 it prints Deinit once before Initing (unexpected) AND once after (expected). On swift 6.0 nightly it apparently crashes (see forum replies for this).

Environment

Version with miscompile:
$ swiftc --version
swift-driver version: 1.90.11.1 Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)
Target: arm64-apple-macosx14.0

Version with crash:
Apple Swift version 6.0-dev (LLVM 4b0b1f9e1a69523, Swift 91a3abc)

Additional information

No response

[tbkka]

CC: @kavon @jckarter