Merge pull request swiftlang#69256 from kubamracek/embedded-arc-crash

[embedded] Fix an LLVMARCOpts crash by avoiding direct calls to swift_retain/swift_release

Author: kubamracek

stdlib/public/core/EmbeddedRuntime.swift

@@ -131,7 +131,9 @@ public func swift_isUniquelyReferenced_nonNull_native(object: UnsafeMutablePoint
 
 @_silgen_name("swift_retain")
 public func swift_retain(object: Builtin.RawPointer) -> Builtin.RawPointer {
-  return swift_retain_n(object: object, n: 1)
+  if Int(Builtin.ptrtoint_Word(object)) == 0 { return object }
+  let o = UnsafeMutablePointer<HeapObject>(object)
+  return swift_retain_n_(object: o, n: 1)._rawValue
 }
 
 // Cannot use UnsafeMutablePointer<HeapObject>? directly in the function argument or return value as it causes IRGen crashes
@@ -155,7 +157,9 @@ func swift_retain_n_(object: UnsafeMutablePointer<HeapObject>, n: UInt32) -> Uns
 
 @_silgen_name("swift_release")
 public func swift_release(object: Builtin.RawPointer) {
-  swift_release_n(object: object, n: 1)
+  if Int(Builtin.ptrtoint_Word(object)) == 0 { return }
+  let o = UnsafeMutablePointer<HeapObject>(object)
+  swift_release_n_(object: o, n: 1)
 }
 
 @_silgen_name("swift_release_n")

test/embedded/ouroboros-bug.swift

@@ -0,0 +1,15 @@
+// Regression test for a "Ouroboros Bug": The ARC optimizer doesn't like the
+// presense of a direct call to swift_retain and swift_release in any Swift
+// code, but in the embedded Swift's runtime that's somewhat reasonable thing
+// to do (but is to be avoided because of this).
+
+// RUN: %target-swift-frontend -target armv7-apple-none-macho -assert-config Debug -Osize -Xcc -D__MACH__ -emit-ir %s -enable-experimental-feature Embedded | %FileCheck %s
+// RUN: %target-swift-frontend -target arm64-apple-none-macho -assert-config Debug -Osize -Xcc -D__MACH__ -Xcc -D__arm64__ -Xcc -D__APPLE__ -emit-ir %s -enable-experimental-feature Embedded | %FileCheck %s
+
+// REQUIRES: VENDOR=apple
+// REQUIRES: optimized_stdlib
+
+public func test() {}
+test()
+
+// CHECK: define {{.*}}i32 @main