Certain deinit's on ~Copyable types fail to compile

[rvsrvs]

Description

The following code fails to compile using Xcode 15b8:

struct Example: ~Copyable {
    private var failureString: String { "Goodbye." }
    deinit { fatalError("FATAL ERROR: \(failureString)") }
}

It produces the error:

Usage of a noncopyable type that compiler can't verify. This is a compiler bug. Please file a bug with a small example of the bug

Steps to reproduce

Cut and paste the above struct into a playground and observe the compiler error

Expected behavior

It should compile and, when run, the deinit should cause a fatal error to occur with the correct error message.

Environment

• Swift Version: swift-driver version: 1.87.1 Apple Swift version 5.9 (swiftlang-5.9.0.128.106 clang-1500.0.40.1)
  Target: arm64-apple-macosx13.0
• Xcode Version: Xcode 15.0, Build version 15A5229m
• Deployment target: all

[gottesmm]

PrunedLiveness does not understand something here. It isn't a move checker bug:

frame #15: 0x0000000100a69aa4 swift-frontend`swift::siloptimizer::MoveOnlyObjectChecker::check(llvm::SmallSetVector<swift::MarkUnresolvedNonCopyableValueInst*, 32u>&) at MoveOnlyObjectCheckerUtils.cpp:621:25 [opt]
   618 	
   619 	    // Step 1. Compute liveness.
   620 	    if (!canonicalizer.computeLiveness()) {
-> 621 	      diagnosticEmitter.emitCheckerDoesntUnderstandDiagnostic(markedValue);
   622 	      LLVM_DEBUG(
   623 	          llvm::dbgs()
   624 	          << "Emitted checker doesnt understand diagnostic! Exiting early!\n");
(lldb)

@atrick

[nate-chandler]

Fixed by #68342 .

Tracked internally as rdar://115185992 .