[SILGen] Emit runtime actor isolation checks for @objc thunks of closures

Author: xedin

lib/SILGen/SILGenBridging.cpp

@@ -1597,8 +1597,15 @@ void SILGenFunction::emitNativeToForeignThunk(SILDeclRef thunk) {
       getASTContext().LangOpts.hasFeature(Feature::PreconcurrencyConformances);
 
   llvm::Optional<ActorIsolation> isolation;
-  if ((F.isAsync() || emitExecutorPrecondition) && thunk.hasDecl()) {
-    isolation = getActorIsolation(thunk.getDecl());
+  if (F.isAsync()) {
+    if (thunk.hasDecl())
+      isolation = getActorIsolation(thunk.getDecl());
+  } else if (emitExecutorPrecondition) {
+    if (thunk.hasDecl()) {
+      isolation = getActorIsolation(thunk.getDecl());
+    } else if (auto globalActor = nativeInfo.FormalType->getGlobalActor()) {
+      isolation = ActorIsolation::forGlobalActor(globalActor);
+    }
   }
 
   // A hop/check is only needed in the thunk if it is global-actor isolated.

lib/Sema/CSApply.cpp

@@ -7442,10 +7442,15 @@ Expr *ExprRewriter::coerceToType(Expr *expr, Type toType,
           if (!(overload && overload->choice.isDecl()))
             return false;
 
-          auto *overloadModule = overload->choice.getDecl()->getModuleContext();
-          return overloadModule != dc->getParentModule() &&
-                 !overloadModule->getLanguageVersionBuiltWith()
-                      .isVersionAtLeast(6);
+          auto *decl = overload->choice.getDecl();
+          // Function values passed to C/ObjC APIs are already thunked
+          // and that's where the check is going to go.
+          if (decl->hasClangNode())
+            return false;
+
+          auto *declaredIn = decl->getModuleContext();
+          return declaredIn && declaredIn != dc->getParentModule() &&
+                 !declaredIn->getLanguageVersionBuiltWith().isVersionAtLeast(6);
         };
 
         if (requiresRuntimeCheck()) {

test/Concurrency/dynamic_checks_for_func_refs_in_preconcurrency_apis_objc.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-experimental-feature PreconcurrencyConformances -emit-silgen -verify %s | %FileCheck %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+install_global_event_handler { @MainActor _ in
+  // expected-warning@-1 {{converting function value of type '@MainActor (Any) -> ()' to 'event_handler' (aka '@convention(c) (Any) -> ()') loses global actor 'MainActor'; this is an error in Swift 6}}
+}
+
+// CHECK-LABEL: sil private [thunk] [ossa] @$s56dynamic_checks_for_func_refs_in_preconcurrency_apis_objcyypScMYccfU_To : $@convention(c) (AnyObject) -> ()
+// CHECK: [[MAIN_ACTOR_METATYPE:%.*]] = metatype $@thick MainActor.Type
+// CHECK: [[SHARED_FIELD_GETTER:%.*]] = function_ref @$sScM6sharedScMvgZ : $@convention(method) (@thick MainActor.Type) -> @owned MainActor
+// CHECK-NEXT: [[MAIN_ACTOR:%.*]] = apply [[SHARED_FIELD_GETTER]]([[MAIN_ACTOR_METATYPE]]) : $@convention(method) (@thick MainActor.Type) -> @owned MainActor
+// CHECK-NEXT: [[MAIN_ACTOR_ACCESS:%.*]] = begin_borrow [[MAIN_ACTOR]] : $MainActor
+// CHECK-NEXT: [[EXEC:%.*]] = extract_executor [[MAIN_ACTOR_ACCESS]] : $MainActor
+// CHECK: [[CHECK_EXEC_REF:%.*]] = function_ref @$ss22_checkExpectedExecutor14_filenameStart01_D6Length01_D7IsASCII5_line9_executoryBp_BwBi1_BwBetF
+// CHECK-NEXT: {{.*}} = apply [[CHECK_EXEC_REF]]({{.*}}, [[EXEC]])