[silgen] Make async_Main compatible with calling nonisolated(nonsending) functions.

The problem is that async_Main was setting an executor as its main executor
instead of an actor. This patch fixes the issue by just grabbing the main actor
instead.

rdar://153082633

Author: gottesmm

lib/SILGen/SILGenTopLevel.cpp

@@ -65,26 +65,31 @@ void SILGenModule::emitEntryPoint(SourceFile *SF, SILFunction *TopLevel) {
 
   auto prologueLoc = RegularLocation::getModuleLocation();
   prologueLoc.markAsPrologue();
-  if (SF->isAsyncContext()) {
-    // emitAsyncMainThreadStart will create argc and argv.
-    // Just set the main actor as the expected executor; we should
-    // already be running on it.
-    SILValue executor = TopLevelSGF.emitMainExecutor(prologueLoc);
-    TopLevelSGF.ExpectedExecutor.set(TopLevelSGF.B.createOptionalSome(
-        prologueLoc, executor, SILType::getOptionalType(executor->getType())));
-  } else {
-    // Create the argc and argv arguments.
-    auto entry = TopLevelSGF.B.getInsertionBB();
-    auto context = TopLevelSGF.getTypeExpansionContext();
-    auto paramTypeIter =
-        TopLevelSGF.F.getConventions().getParameterSILTypes(context).begin();
-
-    entry->createFunctionArgument(*paramTypeIter);
-    entry->createFunctionArgument(*std::next(paramTypeIter));
-  }
 
   {
     Scope S(TopLevelSGF.Cleanups, moduleCleanupLoc);
+
+    if (SF->isAsyncContext()) {
+      // emitAsyncMainThreadStart will create argc and argv.
+      // Just set the main actor as the expected executor; we should
+      // already be running on it.
+      auto mainActorType =
+          getASTContext().getMainActorType()->getCanonicalType();
+      TopLevelSGF.ExpectedExecutor.set(
+          TopLevelSGF.emitGlobalActorIsolation(prologueLoc, mainActorType)
+              .borrow(TopLevelSGF, prologueLoc)
+              .getValue());
+    } else {
+      // Create the argc and argv arguments.
+      auto entry = TopLevelSGF.B.getInsertionBB();
+      auto context = TopLevelSGF.getTypeExpansionContext();
+      auto paramTypeIter =
+          TopLevelSGF.F.getConventions().getParameterSILTypes(context).begin();
+
+      entry->createFunctionArgument(*paramTypeIter);
+      entry->createFunctionArgument(*std::next(paramTypeIter));
+    }
+
     SILGenTopLevel(TopLevelSGF).visitSourceFile(SF);
   }
 

test/SILGen/toplevel_globalactorvars.swift

@@ -3,10 +3,14 @@
 // a
 // CHECK-LABEL: sil_global hidden @$s24toplevel_globalactorvars1aSivp : $Int
 
-// CHECK-LABEL: sil private [ossa] @async_Main
+// CHECK-LABEL: sil private [ossa] @async_Main : $@convention(thin) @async () -> () {
 // CHECK: bb0:
-// CHECK-NEXT: [[MAIN:%.*]] = builtin "buildMainActorExecutorRef"() : $Builtin.Executor
-// CHECK-NEXT: [[MAIN_OPTIONAL:%[0-9]+]] = enum $Optional<Builtin.Executor>, #Optional.some!enumelt, [[MAIN]]
+// CHECK: [[META:%.*]] = metatype $@thick MainActor.Type
+// CHECK: [[FUNC:%.*]] = function_ref @$sScM6sharedScMvgZ : $@convention(method) (@thick MainActor.Type) -> @owned MainActor
+// CHECK: [[ACTOR_RAW:%.*]] = apply [[FUNC]]([[META]])
+// CHECK: [[ACTOR_RAW_E:%.*]] = init_existential_ref [[ACTOR_RAW]]
+// CHECK: [[ACTOR_RAW_E_O:%.*]] = enum $Optional<any Actor>, #Optional.some!enumelt, [[ACTOR_RAW_E]]
+// CHECK: [[ACTOR:%.*]] = begin_borrow [[ACTOR_RAW_E_O]]
 
 actor MyActorImpl {}
 
@@ -67,7 +71,7 @@ await printFromMyActor(value: a)
 // CHECK: hop_to_executor [[ACTORREF]] : $MyActorImpl
 // CHECK: end_borrow [[ACTORREF]]
 // CHECK: {{%[0-9]+}} = apply [[PRINTFROMMYACTOR_FUNC]]([[AGLOBAL]])
-// CHECK: hop_to_executor [[MAIN_OPTIONAL]]
+// CHECK: hop_to_executor [[ACTOR]]
 
 if a < 10 {
 // CHECK: [[AACCESS:%[0-9]+]] = begin_access [read] [dynamic] [[AREF]] : $*Int
@@ -121,5 +125,12 @@ if a < 10 {
     // CHECK: hop_to_executor [[ACTORREF]] : $MyActorImpl
     // CHECK: end_borrow [[ACTORREF]]
     // CHECK: {{%[0-9]+}} = apply [[PRINTFROMMYACTOR_FUNC]]([[AGLOBAL]])
-    // CHECK: hop_to_executor [[MAIN_OPTIONAL]]
+    // CHECK: hop_to_executor [[ACTOR]]
 }
+
+nonisolated(nonsending) func nonisolatedNonSendingFunction() async {}
+
+// CHECK: [[FUNC:%.*]] = function_ref @$s24toplevel_globalactorvars29nonisolatedNonSendingFunctionyyYaF : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+// CHECK: apply [[FUNC]]([[ACTOR]])
+// CHECK-NEXT: hop_to_executor [[ACTOR]]
+await nonisolatedNonSendingFunction()