Add more regression tests

validation-test/compiler_crashers_fixed/issue-46986.swift

@@ -0,0 +1,4 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+struct Foo : ExpressibleByUnicodeScalarLiteral {}
+let _: Foo = "\\"

validation-test/compiler_crashers_fixed/issue-47195.swift

@@ -0,0 +1,11 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+extension Dictionary {
+  init<S: Sequence>(grouping elements: S, by keyForValue: (S.Iterator.Element) -> Key)
+    where Value : RangeReplaceableCollection, Value.Iterator.Element == S.Iterator.Element {
+    self = [:]
+  }
+}
+
+let names = ["Patti", "Aretha", "Anita", "Gladys"]
+print(Dictionary(grouping: names, by: { $0.utf16.count }))

validation-test/compiler_crashers_fixed/issue-47769.swift

@@ -0,0 +1,17 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+struct _MyError: ExpressibleByIntegerLiteral {
+    typealias IntegerLiteralType = Int
+
+    private var _underlyingValue: _MyError.IntegerLiteralType
+    var httpErrorCode: UInt = 0
+
+    public init(integerLiteral value: _MyError.IntegerLiteralType) {
+        _underlyingValue = value
+    }
+}
+
+enum MyError: _MyError, Error {
+    typealias RawValue = Int
+    case caseOne = 0
+}

validation-test/compiler_crashers_fixed/issue-51794.swift

@@ -0,0 +1,17 @@
+// RUN: %target-swift-frontend -emit-ir %s
+
+protocol Prot {
+    var prop: String { get }
+}
+
+class Gen<A: Prot> { }
+
+class Real: Gen<Real.RealProt> {
+    enum RealProt: Prot {
+        case first
+
+        var prop: String {
+            return "hello"
+        }
+    }
+}

validation-test/compiler_crashers_fixed/issue-52891.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend -emit-ir %s
+// REQUIRES: objc_interop
+
+import Foundation
+
+class C {
+  @objc func foo() -> String! { return nil }
+}
+
+func bar(_ x: AnyObject) {
+  let y: String = x.foo!()
+}