Merge pull request swiftlang#12341 from practicalswift/swiftc-28856-typevariables-impl-getgraphindex-typevar-type-variable-mismatch

[swiftc (62 vs. 5600)] Add crasher in swift::constraints::ConstraintGraph::lookupNode(...)

Author: practicalswift

validation-test/compiler_crashers/28856-typevariables-impl-getgraphindex-typevar-type-variable-mismatch.swift

@@ -0,0 +1,10 @@
+// This source file is part of the Swift.org open source project
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+
+// REQUIRES: asserts
+// RUN: not --crash %target-swift-frontend %s -emit-ir
+{[Int?as?ManagedBuffer}{