[Async CC] Always add full type metadata to bindings.

lib/IRGen/GenProto.cpp

@@ -2748,8 +2748,16 @@ void NecessaryBindings::save(IRGenFunction &IGF, Address buffer) const {
 void NecessaryBindings::addTypeMetadata(CanType type) {
   assert(!isa<InOutType>(type));
 
+  // If the bindings are for an async function, we will always need the type
+  // metadata.  The opportunities to reconstruct it available in the context of
+  // partial apply forwarders are not available here.
+  if (forAsyncFunction()) {
+    addRequirement({type, nullptr});
+    return;
+  }
+
   // Bindings are only necessary at all if the type is dependent.
-  if (!type->hasArchetype() && !forAsyncFunction())
+  if (!type->hasArchetype())
     return;
 
   // Break down structural types so that we don't eagerly pass metadata

validation-test/compiler_crashers_2_fixed/rdar71816041.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-frontend -emit-ir -primary-file %s -enable-experimental-concurrency
+
+func getIntAndString() async -> (Int, String) { (5, "1") }
+
+func testDecompose() async -> Int {
+  async let (i, s) = await getIntAndString()
+  return await i
+}