SILGen: Don't explode inout tuples in init allocating entry points.

rdar://problem/51302498

Author: jckarter

lib/SILGen/SILGenProlog.cpp

@@ -311,8 +311,8 @@ static void makeArgument(Type ty, ParamDecl *decl,
                          SmallVectorImpl<SILValue> &args, SILGenFunction &SGF) {
   assert(ty && "no type?!");
 
-  // Destructure tuple arguments.
-  if (TupleType *tupleTy = ty->getAs<TupleType>()) {
+  // Destructure tuple value arguments.
+  if (TupleType *tupleTy = decl->isInOut() ? nullptr : ty->getAs<TupleType>()) {
     for (auto fieldType : tupleTy->getElementTypes())
       makeArgument(fieldType, decl, args, SGF);
   } else {

test/SILGen/initializers.swift

@@ -1147,3 +1147,10 @@ extension MemberInits {
     // CHECK-NEXT:  = apply [[INIT_FN]]<Array<T>>() : $@convention(thin) <τ_0_0 where τ_0_0 : Equatable> () -> @owned String
   }
 }
+
+// rdar://problem/51302498
+
+class Butt {
+  init(foo: inout (Int, Int)) { }
+}
+