Add regression test for rdar://problem/91771352

Author: slavapestov

test/Generics/rdar91771352.swift

@@ -0,0 +1,31 @@
+// RUN: %target-typecheck-verify-swift
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures 2>&1 | %FileCheck %s
+
+public struct G<T: P1, U: P1> {
+  // CHECK-LABEL: .f1()@
+  // CHECK-NEXT: Generic signature: <T, U where T : P1, T == U>
+  public func f1() where T == U {}
+
+  // CHECK-LABEL: .f2()@
+  // CHECK-NEXT: Generic signature: <T, U where T : P1, T == U>
+  public func f2() where T == U, T.A.B == T {}
+  // expected-warning@-1 {{redundant same-type constraint 'T.A.B' == 'T'}}
+
+  // CHECK-LABEL: .f3()@
+  // CHECK-NEXT: Generic signature: <T, U where T : P1, T == U>
+  public func f3() where T.A.B == T, T == U {}
+  // expected-warning@-1 {{redundant same-type constraint 'T.A.B' == 'T'}}
+
+  // CHECK-LABEL: .f4()@
+  // CHECK-NEXT: Generic signature: <T, U where T : P1, T == U>
+  public func f4() where U.A.B == U, T == U {}
+  // expected-warning@-1 {{redundant same-type constraint 'U.A.B' == 'U'}}
+}
+
+public protocol P1 {
+  associatedtype A: P2 where A.B == Self
+}
+
+public protocol P2 {
+  associatedtype B: P1
+}