Merge pull request swiftlang#39680 from kateinoigakukun/katei/fix-ill-unreachable-coro-end

[IRGen] Put 'ret void' instead of unreachable for non swiftasync cc

Author: DougGregor

lib/IRGen/GenCall.cpp

@@ -4982,7 +4982,15 @@ void irgen::emitAsyncReturn(
     arguments.push_back(arg);
 
   Builder.CreateIntrinsicCall(llvm::Intrinsic::coro_end_async, arguments);
-  Builder.CreateUnreachable();
+
+  if (IGF.IGM.AsyncTailCallKind == llvm::CallInst::TCK_MustTail) {
+    Builder.CreateUnreachable();
+  } else {
+    // If target doesn't support musttail (e.g. WebAssembly), the function
+    // passed to coro.end.async can return control back to the caller.
+    // So use ret void instead of unreachable to allow it.
+    Builder.CreateRetVoid();
+  }
 }
 
 void irgen::emitAsyncReturn(IRGenFunction &IGF, AsyncContextLayout &asyncLayout,

test/IRGen/async/non_musttail_target.sil

@@ -0,0 +1,17 @@
+// Ensure that IRGen don't emit unreachable after coro.end.async for targets that don't support musttail call.
+// RUN: %swift -disable-legacy-type-info -parse-stdlib -target wasm32-unknown-wasi %s -disable-llvm-optzns -disable-swift-specific-llvm-optzns -disable-objc-interop -module-name main -emit-ir -o - | %FileCheck %s
+// REQUIRES: concurrency
+// REQUIRES: CODEGENERATOR=WebAssembly
+
+sil_stage canonical
+
+import Builtin
+
+sil @test_simple : $@async () -> () {
+bb0:
+  %0 = tuple ()
+  return %0 : $()
+// CHECK:     call i1 (i8*, i1, ...) @llvm.coro.end.async
+// CHECK-NOT: unreachable
+// CHECK:     ret void
+}