[concurrency] SILGen: only emit hop_to_executor instructions in async functions.

Author: eeckstein

lib/SILGen/SILGenProlog.cpp

@@ -451,6 +451,9 @@ void SILGenFunction::emitProlog(CaptureInfo captureInfo,
     }
   }
 
+  if (!F.isAsync())
+    return;
+
   if (auto *funcDecl =
         dyn_cast_or_null<AbstractFunctionDecl>(FunctionDC->getAsDecl())) {
     auto actorIsolation = getActorIsolation(funcDecl);

test/SILGen/hop_to_executor.swift

@@ -47,6 +47,13 @@ actor class MyActor {
     await callee(p)
   }
 
+  // CHECK-LABEL: sil hidden [ossa] @$s4test7MyActorC13dontInsertHTESiyF : $@convention(method) (@guaranteed MyActor) -> Int {
+  // CHECK-NOT:   hop_to_executor
+  // CHECK:     } // end sil function '$s4test7MyActorC13dontInsertHTESiyF'
+  func dontInsertHTE() -> Int {
+    return p
+  }
+
   init() {
     p = 27
   }