SILGen: do not emit hop_to_executor in some objc thunks

An @objc async thunk does not need to perform a
hop_to_executor if the native method the thunk is
wrapping is async, since the native method will do
its own hop.

This redundant hop was causing a crash in SILGen
with async actor-instance isolated @objc methods
declared in an actor, because SILGen was not
prepared to add the hop to  to `self` within
the @objc thunk.

resolves rdar://80130628

Author: kavon

lib/SILGen/SILGenBridging.cpp

@@ -1568,8 +1568,10 @@ void SILGenFunction::emitNativeToForeignThunk(SILDeclRef thunk) {
     if (thunk.hasDecl()) {
       isolation = getActorIsolation(thunk.getDecl());
     }
-    
-    if (isolation) {
+
+    // A hop is only needed in the thunk if it is global-actor isolated.
+    // Native, instance-isolated async methods will hop in the prologue.
+    if (isolation && isolation->isGlobalActor()) {
       emitHopToTargetActor(loc, *isolation, None);
     }
   }

test/Concurrency/actor_isolation_objc.swift

@@ -53,5 +53,15 @@ func outside(a : A) async {
   await a.i() // expected-warning {{no 'async' operations occur within 'await' expression}}
 }
 
+actor Dril: NSObject {
+  // expected-note@+2 {{add 'async' to function 'postSynchronouslyTo(twitter:)' to make it asynchronous}}
+  // expected-error@+1 {{actor-isolated instance method 'postSynchronouslyTo(twitter:)' cannot be @objc}}
+  @objc func postSynchronouslyTo(twitter msg: String) -> Bool {
+    return true
+  }
 
-
+  @MainActor
+  @objc func postFromMainActorTo(twitter msg: String) -> Bool {
+    return true
+  }
+}

test/SILGen/objc_async_from_swift.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -I %S/Inputs/custom-modules -enable-experimental-concurrency -disable-availability-checking %s -verify | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-silgen -I %S/Inputs/custom-modules -enable-experimental-concurrency -disable-availability-checking %s -verify | %FileCheck --implicit-check-not=hop_to_executor --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
 // REQUIRES: concurrency
 // REQUIRES: objc_interop
 
@@ -114,9 +114,44 @@ class SlowServerlet: SlowServer {
 
 @FooActor
 class ActorConstrained: NSObject {
-    // CHECK-LABEL: sil shared [thunk] [ossa] @$s{{.*}}16ActorConstrainedC3foo{{.*}}U_To
+    // ActorConstrained.foo()
+    // CHECK-LABEL: sil hidden [ossa] @$s{{.*}}16ActorConstrainedC3foo{{.*}} : $@convention(method) @async (@guaranteed ActorConstrained) -> Bool {
     // CHECK:         hop_to_executor {{%.*}} : $FooActor
+
+    // @objc ActorConstrained.foo()
+    // CHECK-LABEL: sil hidden [thunk] [ossa] @$s{{.*}}16ActorConstrainedC3foo{{.*}}To : $@convention(objc_method) (@convention(block) (Bool) -> (), ActorConstrained) -> () {
+    // CHECK:         [[ASYNC_CLOS:%[0-9]+]] = function_ref @$s{{.*}}16ActorConstrainedC3foo{{.*}}U_To : $@convention(thin) @Sendable @async (@convention(block) (Bool) -> (), ActorConstrained) -> ()
+    // CHECK:         [[PRIMED_CLOS:%[0-9]+]] = partial_apply [callee_guaranteed] [[ASYNC_CLOS]](
+    // CHECK:         [[TASK_RUNNER:%[0-9]+]] = function_ref @$ss29_runTaskForBridgedAsyncMethodyyyyYaYbcnF
+    // CHECK:         apply [[TASK_RUNNER]]([[PRIMED_CLOS]])
+
+    // @objc closure #1 in ActorConstrained.foo()
+    // CHECK-LABEL: sil shared [thunk] [ossa] @$s{{.*}}16ActorConstrainedC3foo{{.*}}U_To : $@convention(thin) @Sendable @async (@convention(block) (Bool) -> (), ActorConstrained) -> () {
+    // CHECK:           hop_to_executor {{%.*}} : $FooActor
     @objc func foo() async -> Bool {
         return true
     }
 }
+
+
+actor Dril: NSObject {
+    // Dril.postTo(twitter:)
+    // CHECK-LABEL: sil hidden [ossa] @$s{{.*}}4DrilC6postTo7twitter{{.*}} : $@convention(method) @async (@guaranteed String, @guaranteed Dril) -> Bool {
+    // CHECK:           hop_to_executor {{%.*}} : $Dril
+
+    // @objc Dril.postTo(twitter:)
+    // CHECK-LABEL: sil hidden [thunk] [ossa] @$s{{.*}}4DrilC6postTo7twitter{{.*}}To : $@convention(objc_method) (NSString, @convention(block) (Bool) -> (), Dril) -> () {
+    // CHECK:         [[ASYNC_CLOS:%[0-9]+]] = function_ref @$s{{.*}}4DrilC6postTo7twitter{{.*}}U_To : $@convention(thin) @Sendable @async (NSString, @convention(block) (Bool) -> (), Dril) -> ()
+    // CHECK:         [[PRIMED_CLOS:%[0-9]+]] = partial_apply [callee_guaranteed] [[ASYNC_CLOS]](
+    // CHECK:         [[TASK_RUNNER:%[0-9]+]] = function_ref @$ss29_runTaskForBridgedAsyncMethodyyyyYaYbcnF
+    // CHECK:         apply [[TASK_RUNNER]]([[PRIMED_CLOS]])
+    @objc func postTo(twitter msg: String) async -> Bool {
+        return true
+    }
+
+    // this is known to not emit a hop in the objc thunk (rdar://80972126)
+    @MainActor
+    @objc func postFromMainActorTo(twitter msg: String) -> Bool {
+        return true
+    }
+}