Add regression test for rdar://problem/90506457

Author: slavapestov

test/Generics/rdar90506457.swift

@@ -0,0 +1,44 @@
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures -requirement-machine-protocol-signatures=on 2>&1 | %FileCheck %s
+
+// CHECK-LABEL: .P1@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P1]B : P2, Self.[P1]C : P4, Self.[P1]D : P5, Self.[P1]E : P6, Self.[P1]F : P3, Self.[P1]G == Self.[P1]B.[P2]G, Self.[P1]B.[P2]G == Self.[P1]C.[P4]G, Self.[P1]C.[P4]G == Self.[P1]D.[P5]G, Self.[P1]D.[P5]G == Self.[P1]E.[P6]G, Self.[P1]F.[Sequence]Element == SIMD2<Self.[P1]G>>
+public protocol P1 {
+  associatedtype G
+  associatedtype B: P2 where B.G == G
+  associatedtype C: P4 where C.G == G
+  associatedtype D: P5 where D.G == G
+  associatedtype E: P6 where E.G == G
+  associatedtype F: P3 where F.Element == SIMD2<G>
+}
+
+// CHECK-LABEL: .P2@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P2]A : P1, Self.[P2]C : P4, Self.[P2]D : P5, Self.[P2]E : P6, Self.[P2]G == Self.[P2]A.[P1]G, Self.[P2]A.[P1]G == Self.[P2]C.[P4]G, Self.[P2]C.[P4]G == Self.[P2]D.[P5]G, Self.[P2]D.[P5]G == Self.[P2]E.[P6]G>
+public protocol P2 {
+  associatedtype G
+  associatedtype A: P1 where A.G == G
+  associatedtype C: P4 where C.G == G
+  associatedtype D: P5 where D.G == G
+  associatedtype E: P6 where E.G == G
+}
+
+// CHECK-LABEL: .P3@
+// CHECK-NEXT: Requirement signature: <Self where Self : MutableCollection, Self : RandomAccessCollection, Self.[Collection]Index == Int>
+public protocol P3: RandomAccessCollection, MutableCollection where Index == Int {}
+
+// CHECK-LABEL: .P4@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P4]G : SIMDScalar>
+public protocol P4 {
+  associatedtype G: SIMDScalar
+}
+
+// CHECK-LABEL: .P5@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P5]G : SIMDScalar>
+public protocol P5 {
+  associatedtype G: SIMDScalar
+}
+
+// CHECK-LABEL: .P6@
+// CHECK-NEXT: Requirement signature: <Self where Self.[P6]G : SIMDScalar>
+public protocol P6 {
+  associatedtype G: SIMDScalar
+}