[IRGen] Add indirect typed error slot when async function has indirec…

lib/IRGen/GenCall.cpp

@@ -3027,11 +3027,7 @@ class AsyncCallEmission final : public CallEmission {
 
         if (nativeSchema.requiresIndirect() ||
             errorSchema.shouldReturnTypedErrorIndirectly() ||
-            (errorSchema.empty() &&
-             fnConv.hasIndirectSILResults())) { // direct empty typed errors are
-                                                // passed
-          // indirectly for compatibility with generic
-          // functions.
+            fnConv.hasIndirectSILResults()) {
           // Return the error indirectly.
           auto buf = IGF.getCalleeTypedErrorResultSlot(silErrorTy);
           Args[--LastArgWritten] = buf.getAddress();

test/IRGen/typed_throws.swift

@@ -295,3 +295,18 @@ enum LargeError: Error {
 func callClosureAsyncIndirectError(f: () async throws(LargeError) -> Int) async throws(LargeError) -> Int {
   return try await f()
 }
+
+protocol AsyncGenProto<A> {
+  associatedtype A
+  func fn(arg: Int) async throws(SmallError) -> A
+}
+
+// CHECK: define internal swifttailcc void @"$s12typed_throws23callAsyncIndirectResult1p1xxAA0D8GenProto_px1ARts_XP_SitYaAA10SmallErrorVYKlFTY0_"(ptr swiftasync %0)
+// CHECK:   musttail call swifttailcc void {{%.*}}(ptr noalias {{%.*}}, ptr swiftasync {{%.*}}, i64 {{%.*}}, ptr noalias swiftself {{%.*}}, ptr %swifterror, ptr {{%.*}}, ptr {{%.*}})
+// CHECK:   ret void
+// CHECK: }
+@inline(never)
+func callAsyncIndirectResult<A>(p: any AsyncGenProto<A>, x: Int) async throws(SmallError) -> A {
+  return try await p.fn(arg: x)
+}
+

test/Interpreter/typed_throws_abi.swift

@@ -285,10 +285,35 @@ func checkAsync() async {
     await invoke { try await impl.nonMatching_f1(false) }
 }
 
+enum MyError: Error {
+    case x
+    case y
+}
+
+protocol AsyncGenProto<A> {
+  associatedtype A
+  func fn(arg: Int) async throws(MyError) -> A
+}
+
+@inline(never)
+func callAsyncIndirectResult<A>(p: any AsyncGenProto<A>, x: Int) async throws(MyError) -> A {
+  return try await p.fn(arg: x)
+}
+
+
+struct AsyncGenProtoImpl: AsyncGenProto {
+    func fn(arg: Int) async throws(MyError) -> Int {
+        print("Arg is \(arg)")
+        return arg
+    }
+}
+
 @main
 public struct Main {
     public static func main() async {
         await checkSync()
         await checkAsync()
+        // CHECK: Arg is 10
+        print(try! await callAsyncIndirectResult(p: AsyncGenProtoImpl(), x: 10))
     }
 }