IRGen: Fix typo in MetadataPath::followComponent()

This is a regression from a recent change, where I meant to write
dyn_cast<> instead of cast<>.

Author: slavapestov

lib/IRGen/GenProto.cpp

@@ -2666,7 +2666,7 @@ MetadataResponse MetadataPath::followComponent(IRGenFunction &IGF,
       CanType baseSubstType =
         sourceConformance.getAssociatedType(sourceType, depMemType.getBase())
           ->getCanonicalType();
-      if (auto archetypeType = cast<ArchetypeType>(baseSubstType)) {
+      if (auto archetypeType = dyn_cast<ArchetypeType>(baseSubstType)) {
         AssociatedType baseAssocType(depMemType->getAssocType());
 
         MetadataResponse response =

test/Generics/rdar83894546_2.swift

@@ -0,0 +1,42 @@
+// RUN: %target-typecheck-verify-swift
+// RUN: %target-swift-frontend -emit-ir %s
+
+public struct G<A : P7> : P2 {}
+
+public protocol P1 {
+  associatedtype A
+}
+
+public protocol P2: P1 where A: P7 {}
+
+public protocol P3 {
+  associatedtype B: P1 where B.A == A
+  associatedtype A: P7
+}
+
+public protocol P4: P3 where B == G<A> { }
+
+public protocol P5 : P3 {
+  associatedtype C: P3 where C.A == A
+}
+
+public protocol P6 : P5 where B == G<A>, C: P4 {}
+
+public protocol P7 {
+  associatedtype D: P1 where D.A == Self
+}
+
+public protocol P8 {
+  associatedtype E: P5 where E.C.B: P2
+  associatedtype F: P4 where F.A == E.A
+}
+
+public protocol P9 : P8 where E.C == F, E: P6 {}
+
+public func callee<T : P1>(_: T.Type) -> T {
+  fatalError()
+}
+
+public func callee<T : P9>(_: T) {
+  _ = callee(T.F.A.D.self)
+}