Add test case for https://bugs.swift.org/browse/SR-1816

Author: slavapestov

test/SILGen/subscripts.swift

@@ -51,6 +51,10 @@ do {
   v[] = 0
   inoutFunc(&v[])
 
+  _ = v[1]
+  v[1] = 0
+  inoutFunc(&v[1])
+
   _ = v[0, 1, 2]
   v[0, 1, 2] = 3
   inoutFunc(&v[0, 1, 2])
@@ -77,3 +81,55 @@ do {
   inoutFunc(&v["", 0, 1, 2])
 }
 
+struct VariadicSubscript3 {
+  subscript(indices: (Int, Int)...) -> Int {
+    get { return 0 }
+    set {}
+  }
+}
+
+do {
+  var b = VariadicSubscript3()
+  _ = b[]
+  b[] = 1
+  inoutFunc(&b[])
+
+  _ = b[(1, 2)]
+  b[(1,2)] = 1
+  inoutFunc(&b[(1,2)])
+
+  _ = b[(1, 2),(2,3)]
+  b[(1,2),(2,3)] = 1
+  inoutFunc(&b[(1,2),(2,3)])
+}
+
+// https://bugs.swift.org/browse/SR-1816
+public struct Flags: OptionSet {
+  public var rawValue: Int
+  public init(rawValue: Int) { self.rawValue = rawValue }
+
+  public static let flag = Flags(rawValue: 1 << 0)
+}
+
+class VariadicSubscript4 {
+  subscript(_ values: Int..., flags flags: Flags) -> Int {
+    get { return 0 }
+    set { }
+  }
+}
+
+do {
+  let t = VariadicSubscript4()
+
+  _ = t[flags: .flag]
+  t[flags: .flag] = 0
+  inoutFunc(&t[flags: .flag])
+
+  _ = t[1, flags: .flag]
+  t[1, flags: .flag] = 0
+  inoutFunc(&t[1, flags: .flag])
+
+  _ = t[1, 2, 3, flags: .flag]
+  t[1, 2, 3, flags: .flag] = 0
+  inoutFunc(&t[1, 2, 3, flags: .flag])
+}