Add test to exercise Indirect_In codepaths in DistributedAccessor emit

Author: ktoso

lib/IRGen/GenDistributed.cpp

@@ -475,6 +475,7 @@ void DistributedAccessor::decodeArgument(unsigned argumentIdx,
 
     // Remember to deallocate a copy.
     AllocatedArguments.push_back(stackAddr);
+    // Don't forget to actually store the argument
     arguments.add(stackAddr.getAddressPointer());
     break;
   }

test/IRGen/distributed_func_indirect_in_parameter.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-frontend -emit-ir %s -Xllvm -sil-print-function=takeLarge -swift-version 5 -disable-availability-checking 2>&1 | %IRGenFileCheck %s --dump-input=always
+// UNSUPPORTED: back_deploy_concurrency
+// REQUIRES: concurrency
+// REQUIRES: distributed
+
+import Distributed
+
+// This struct must be "very large" in order to cause it to be passed as `indirect @in`.
+// Specifically, this needs to exercise the DistributedAccessor::decodeArgument paths for `Indirect_In` parameter convention.
+public struct LargeValue : Codable {
+  let field1 : Int64 = 1
+  let field2 : Int64 = 2
+  let field3 : Int64 = 3
+  let field4 : Int64 = 4
+  let field5 : Int64 = 5
+  let field6 : Int64 = 6
+  let field7 : Int64 = 7
+  let field8 : Int64 = 8
+}
+
+distributed actor D {
+  typealias ActorSystem = LocalTestingDistributedActorSystem
+
+  // CHECK: sil hidden [distributed] @takeLarge : $@convention(method) (@in LargeValue, @guaranteed D) -> () {
+  @_silgen_name("takeLarge")
+  distributed func takeLarge(_ l: LargeValue) {}
+}