[IRGen] Strip marker protocols when forming generic metadata requests

Without this might might end up with a single element protocol compositions
which are invalid.

(cherry picked from commit 552749e)

Author: xedin

lib/IRGen/MetadataRequest.cpp

@@ -1989,6 +1989,16 @@ namespace {
 
     MetadataResponse visitExistentialType(CanExistentialType type,
                                           DynamicMetadataRequest request) {
+      if (auto *PCT =
+              type->getConstraintType()->getAs<ProtocolCompositionType>()) {
+        auto constraintTy = PCT->withoutMarkerProtocols();
+        if (constraintTy->getClassOrBoundGenericClass()) {
+          auto response = IGF.emitTypeMetadataRef(
+              constraintTy->getCanonicalType(), request);
+          return setLocal(type, response);
+        }
+      }
+
       if (auto metadata = tryGetLocal(type, request))
         return metadata;
 

test/Interpreter/protocol_composition_with_markers.swift

@@ -27,3 +27,27 @@ do {
   print(v1 == v2)
   // CHECK: true
 }
+
+@_marker
+protocol Marker {
+}
+
+do {
+  print(G<any (C & Sendable)>.self)
+  // CHECK: G<C>
+
+  class D<T> {
+  }
+
+  print((D<Int> & Sendable).self)
+  // CHECK: D<Int>
+
+  print((D<C & Marker> & Sendable).self)
+  // CHECK: D<C>
+
+  print((any Marker & Sendable).self)
+  // CHECK: Any
+
+  print((AnyObject & Sendable & Marker).self)
+  // CHECK: AnyObject
+}