diff --git a/runtime/vm/app_snapshot.cc b/runtime/vm/app_snapshot.cc
index 2b20b44d08f5..da714737b430 100644
--- a/runtime/vm/app_snapshot.cc
+++ b/runtime/vm/app_snapshot.cc
@@ -1873,12 +1873,12 @@ class CodeSerializationCluster : public SerializationCluster {
     // in the current loading unit).
     ObjectPoolPtr pool = code->untag()->object_pool_;
     if (s->kind() == Snapshot::kFullAOT) {
-      TracePool(s, pool, /*only_code=*/is_deferred);
+      TracePool(s, pool, /*only_call_targets=*/is_deferred);
     } else {
       if (s->InCurrentLoadingUnitOrRoot(pool)) {
         s->Push(pool);
       } else {
-        TracePool(s, pool, /*only_code=*/true);
+        TracePool(s, pool, /*only_call_targets=*/true);
       }
     }
 
@@ -1946,7 +1946,7 @@ class CodeSerializationCluster : public SerializationCluster {
 #endif
   }
 
-  void TracePool(Serializer* s, ObjectPoolPtr pool, bool only_code) {
+  void TracePool(Serializer* s, ObjectPoolPtr pool, bool only_call_targets) {
     if (pool == ObjectPool::null()) {
       return;
     }
@@ -1957,8 +1957,18 @@ class CodeSerializationCluster : public SerializationCluster {
       auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
       if (entry_type == ObjectPool::EntryType::kTaggedObject) {
         const ObjectPtr target = pool->untag()->data()[i].raw_obj_;
-        if (!only_code || target->IsCode()) {
+        // A field is a call target because its initializer may be called
+        // indirectly by passing the field to the runtime. A const closure
+        // is a call target because its function may be called indirectly
+        // via a closure call.
+        if (!only_call_targets || target->IsCode() || target->IsFunction() ||
+            target->IsField() || target->IsClosure()) {
           s->Push(target);
+        } else {
+          intptr_t cid = target->GetClassIdMayBeSmi();
+          if (cid >= kNumPredefinedCids) {
+            s->Push(s->isolate_group()->class_table()->At(cid));
+          }
         }
       }
     }
diff --git a/runtime/vm/compiler/aot/precompiler.cc b/runtime/vm/compiler/aot/precompiler.cc
index ee450a677ced..6c6a0239d1ce 100644
--- a/runtime/vm/compiler/aot/precompiler.cc
+++ b/runtime/vm/compiler/aot/precompiler.cc
@@ -424,6 +424,7 @@ Precompiler::Precompiler(Thread* thread)
       typeparams_to_retain_(),
       consts_to_retain_(),
       seen_table_selectors_(),
+      api_uses_(),
       error_(Error::Handle()),
       get_runtime_type_is_unique_(false) {
   ASSERT(Precompiler::singleton_ == NULL);
@@ -662,6 +663,8 @@ void Precompiler::DoCompileAll() {
       ProgramVisitor::Dedup(T);
     }
 
+    PruneDictionaries();
+
     if (retained_reasons_writer_ != nullptr) {
       reasons_writer.Write();
       retained_reasons_writer_ = nullptr;
@@ -752,6 +755,7 @@ void Precompiler::AddRoots() {
     }
   }
   if (!main.IsNull()) {
+    AddApiUse(main);
     if (lib.LookupLocalFunction(name) == Function::null()) {
       retain_root_library_caches_ = true;
     }
@@ -1464,6 +1468,14 @@ bool Precompiler::IsHitByTableSelector(const Function& function) {
   return seen_table_selectors_.HasKey(selector_id);
 }
 
+void Precompiler::AddApiUse(const Object& obj) {
+  api_uses_.Insert(&Object::ZoneHandle(Z, obj.ptr()));
+}
+
+bool Precompiler::HasApiUse(const Object& obj) {
+  return api_uses_.HasKey(&obj);
+}
+
 void Precompiler::AddInstantiatedClass(const Class& cls) {
   if (is_tracing()) {
     tracer_->WriteClassInstantiationRef(cls);
@@ -1523,6 +1535,7 @@ void Precompiler::AddAnnotatedRoots() {
                                  &reusable_object_handle) ==
             EntryPointPragma::kAlways) {
           AddInstantiatedClass(cls);
+          AddApiUse(cls);
         }
       }
 
@@ -1541,6 +1554,7 @@ void Precompiler::AddAnnotatedRoots() {
           if (pragma == EntryPointPragma::kNever) continue;
 
           AddField(field);
+          AddApiUse(field);
 
           if (!field.is_static()) {
             if (pragma != EntryPointPragma::kSetterOnly) {
@@ -1569,6 +1583,7 @@ void Precompiler::AddAnnotatedRoots() {
               type == EntryPointPragma::kCallOnly) {
             functions_with_entry_point_pragmas_.Insert(function);
             AddFunction(function, RetainReasons::kEntryPointPragma);
+            AddApiUse(function);
           }
 
           if ((type == EntryPointPragma::kAlways ||
@@ -1578,10 +1593,16 @@ void Precompiler::AddAnnotatedRoots() {
             function2 = function.ImplicitClosureFunction();
             functions_with_entry_point_pragmas_.Insert(function2);
             AddFunction(function2, RetainReasons::kEntryPointPragma);
+
+            // Not `function2`: Dart_GetField will lookup the regular function
+            // and get the implicit closure function from that.
+            AddApiUse(function);
           }
 
           if (function.IsGenerativeConstructor()) {
             AddInstantiatedClass(cls);
+            AddApiUse(function);
+            AddApiUse(cls);
           }
         }
         if (function.kind() == UntaggedFunction::kImplicitGetter &&
@@ -1591,6 +1612,7 @@ void Precompiler::AddAnnotatedRoots() {
             if (function.accessor_field() == field.ptr()) {
               functions_with_entry_point_pragmas_.Insert(function);
               AddFunction(function, RetainReasons::kImplicitGetter);
+              AddApiUse(function);
             }
           }
         }
@@ -1601,6 +1623,7 @@ void Precompiler::AddAnnotatedRoots() {
             if (function.accessor_field() == field.ptr()) {
               functions_with_entry_point_pragmas_.Insert(function);
               AddFunction(function, RetainReasons::kImplicitSetter);
+              AddApiUse(function);
             }
           }
         }
@@ -1611,9 +1634,15 @@ void Precompiler::AddAnnotatedRoots() {
             if (function.accessor_field() == field.ptr()) {
               functions_with_entry_point_pragmas_.Insert(function);
               AddFunction(function, RetainReasons::kImplicitStaticGetter);
+              AddApiUse(function);
             }
           }
         }
+        if (function.is_native()) {
+          // The embedder will need to lookup this library to provide the native
+          // resolver, even if there are no embedder calls into the library.
+          AddApiUse(lib);
+        }
       }
 
       implicit_getters = GrowableObjectArray::null();
@@ -3069,6 +3098,166 @@ void Precompiler::DiscardCodeObjects() {
   }
 }
 
+void Precompiler::PruneDictionaries() {
+  // PRODUCT-only: pruning interferes with various uses of the service protocol,
+  // including heap analysis tools.
+#if defined(PRODUCT)
+  class PruneDictionariesVisitor {
+   public:
+    GrowableObjectArrayPtr PruneLibraries(
+        const GrowableObjectArray& libraries) {
+      for (intptr_t i = 0; i < libraries.Length(); i++) {
+        lib_ ^= libraries.At(i);
+        bool retain = PruneLibrary(lib_);
+        if (retain) {
+          lib_.set_index(retained_libraries_.Length());
+          retained_libraries_.Add(lib_);
+        } else {
+          lib_.set_index(-1);
+          lib_.set_private_key(null_string_);
+        }
+      }
+
+      Library::RegisterLibraries(Thread::Current(), retained_libraries_);
+      return retained_libraries_.ptr();
+    }
+
+    bool PruneLibrary(const Library& lib) {
+      dict_ = lib.dictionary();
+      intptr_t dict_size = dict_.Length() - 1;
+      intptr_t used = 0;
+      for (intptr_t i = 0; i < dict_size; i++) {
+        entry_ = dict_.At(i);
+        if (entry_.IsNull()) continue;
+
+        bool retain = false;
+        if (entry_.IsClass()) {
+          // dart:async: Fix async stack trace lookups in dart:async to annotate
+          // entry points or fail gracefully.
+          // dart:core, dart:collection, dart:typed_data: Isolate messaging
+          // between groups allows any class in these libraries.
+          retain = PruneClass(Class::Cast(entry_)) ||
+                   (lib.url() == Symbols::DartAsync().ptr()) ||
+                   (lib.url() == Symbols::DartCore().ptr()) ||
+                   (lib.url() == Symbols::DartCollection().ptr()) ||
+                   (lib.url() == Symbols::DartTypedData().ptr());
+        } else if (entry_.IsFunction() || entry_.IsField()) {
+          retain = precompiler_->HasApiUse(entry_);
+        } else {
+          FATAL("Unexpected library entry: %s", entry_.ToCString());
+        }
+        if (retain) {
+          used++;
+        } else {
+          dict_.SetAt(i, Object::null_object());
+        }
+      }
+      lib.RehashDictionary(dict_, used * 4 / 3 + 1);
+
+      bool retain = used > 0;
+      cls_ = lib.toplevel_class();
+      if (PruneClass(cls_)) {
+        retain = true;
+      }
+      if (lib.is_dart_scheme()) {
+        retain = true;
+      }
+      if (lib.ptr() == root_lib_.ptr()) {
+        retain = true;
+      }
+      if (precompiler_->HasApiUse(lib)) {
+        retain = true;
+      }
+      return retain;
+    }
+
+    bool PruneClass(const Class& cls) {
+      bool retain = precompiler_->HasApiUse(cls);
+
+      functions_ = cls.functions();
+      retained_functions_ = GrowableObjectArray::New();
+      for (intptr_t i = 0; i < functions_.Length(); i++) {
+        function_ ^= functions_.At(i);
+        if (precompiler_->HasApiUse(function_)) {
+          retained_functions_.Add(function_);
+          retain = true;
+        } else if (precompiler_->functions_called_dynamically_.ContainsKey(
+                       function_)) {
+          retained_functions_.Add(function_);
+          // No `retain = true`: the function must appear in the method
+          // dictionary for lookup, but the class may still be removed from the
+          // library.
+        }
+      }
+      if (retained_functions_.Length() > 0) {
+        functions_ = Array::MakeFixedLength(retained_functions_);
+        cls.SetFunctions(functions_);
+      } else {
+        cls.SetFunctions(Object::empty_array());
+      }
+
+      fields_ = cls.fields();
+      retained_fields_ = GrowableObjectArray::New();
+      for (intptr_t i = 0; i < fields_.Length(); i++) {
+        field_ ^= fields_.At(i);
+        if (precompiler_->HasApiUse(field_)) {
+          retained_fields_.Add(field_);
+          retain = true;
+        }
+      }
+      if (retained_fields_.Length() > 0) {
+        fields_ = Array::MakeFixedLength(retained_fields_);
+        cls.SetFields(fields_);
+      } else {
+        cls.SetFields(Object::empty_array());
+      }
+
+      return retain;
+    }
+
+    explicit PruneDictionariesVisitor(Precompiler* precompiler, Zone* zone)
+        : precompiler_(precompiler),
+          lib_(Library::Handle(zone)),
+          dict_(Array::Handle(zone)),
+          entry_(Object::Handle(zone)),
+          cls_(Class::Handle(zone)),
+          functions_(Array::Handle(zone)),
+          fields_(Array::Handle(zone)),
+          function_(Function::Handle(zone)),
+          field_(Field::Handle(zone)),
+          retained_functions_(GrowableObjectArray::Handle(zone)),
+          retained_fields_(GrowableObjectArray::Handle(zone)),
+          retained_libraries_(
+              GrowableObjectArray::Handle(zone, GrowableObjectArray::New())),
+          root_lib_(Library::Handle(
+              zone,
+              precompiler->isolate_group()->object_store()->root_library())),
+          null_string_(String::Handle(zone)) {}
+
+   private:
+    Precompiler* const precompiler_;
+    Library& lib_;
+    Array& dict_;
+    Object& entry_;
+    Class& cls_;
+    Array& functions_;
+    Array& fields_;
+    Function& function_;
+    Field& field_;
+    GrowableObjectArray& retained_functions_;
+    GrowableObjectArray& retained_fields_;
+    const GrowableObjectArray& retained_libraries_;
+    const Library& root_lib_;
+    const String& null_string_;
+  };
+
+  HANDLESCOPE(T);
+  SafepointWriteRwLocker ml(T, T->isolate_group()->program_lock());
+  PruneDictionariesVisitor visitor(this, Z);
+  libraries_ = visitor.PruneLibraries(libraries_);
+#endif  // defined(PRODUCT)
+}
+
 // Traits for the HashTable template.
 struct CodeKeyTraits {
   static uint32_t Hash(const Object& key) { return Code::Cast(key).Size(); }
diff --git a/runtime/vm/compiler/aot/precompiler.h b/runtime/vm/compiler/aot/precompiler.h
index 4e0d2117bb25..50df9e7d5945 100644
--- a/runtime/vm/compiler/aot/precompiler.h
+++ b/runtime/vm/compiler/aot/precompiler.h
@@ -210,6 +210,37 @@ class TypeArgumentsKeyValueTrait {
 
 typedef DirectChainedHashMap<TypeArgumentsKeyValueTrait> TypeArgumentsSet;
 
+class ProgramElementKeyValueTrait {
+ public:
+  // Typedefs needed for the DirectChainedHashMap template.
+  typedef const Object* Key;
+  typedef const Object* Value;
+  typedef const Object* Pair;
+
+  static Key KeyOf(Pair kv) { return kv; }
+
+  static Value ValueOf(Pair kv) { return kv; }
+
+  static inline uword Hash(Key key) {
+    if (key->IsFunction()) {
+      return Function::Cast(*key).Hash();
+    } else if (key->IsField()) {
+      return Field::Cast(*key).kernel_offset();
+    } else if (key->IsClass()) {
+      return Class::Cast(*key).kernel_offset();
+    } else if (key->IsLibrary()) {
+      return Library::Cast(*key).index();
+    }
+    FATAL("Unexpected type: %s\n", key->ToCString());
+  }
+
+  static inline bool IsKeyEqual(Pair pair, Key key) {
+    return pair->ptr() == key->ptr();
+  }
+};
+
+typedef DirectChainedHashMap<ProgramElementKeyValueTrait> ProgramElementSet;
+
 class InstanceKeyValueTrait {
  public:
   // Typedefs needed for the DirectChainedHashMap template.
@@ -321,6 +352,8 @@ class Precompiler : public ValueObject {
   bool IsHitByTableSelector(const Function& function);
   // Returns the reason if the function must be retained, otherwise nullptr.
   const char* MustRetainFunction(const Function& function);
+  void AddApiUse(const Object& obj);
+  bool HasApiUse(const Object& obj);
 
   void ProcessFunction(const Function& function);
   void CheckForNewDynamicFunctions();
@@ -343,6 +376,7 @@ class Precompiler : public ValueObject {
   void DropClasses();
   void DropLibraries();
   void DiscardCodeObjects();
+  void PruneDictionaries();
 
   DEBUG_ONLY(FunctionPtr FindUnvisitedRetainedFunction());
 
@@ -393,6 +427,7 @@ class Precompiler : public ValueObject {
   TypeParameterSet typeparams_to_retain_;
   InstanceSet consts_to_retain_;
   TableSelectorSet seen_table_selectors_;
+  ProgramElementSet api_uses_;
   Error& error_;
 
   compiler::DispatchTableGenerator* dispatch_table_generator_;
diff --git a/runtime/vm/compiler/frontend/kernel_translation_helper.cc b/runtime/vm/compiler/frontend/kernel_translation_helper.cc
index d52cc58fba73..7dba48aceeb9 100644
--- a/runtime/vm/compiler/frontend/kernel_translation_helper.cc
+++ b/runtime/vm/compiler/frontend/kernel_translation_helper.cc
@@ -1891,9 +1891,11 @@ void LoadingUnitsMetadataHelper::ReadMetadata(intptr_t node_offset) {
   Zone* zone = thread->zone();
   intptr_t unit_count = helper_->ReadUInt();
   Array& loading_units = Array::Handle(zone, Array::New(unit_count + 1));
+  Array& loading_unit_uris = Array::Handle(zone, Array::New(unit_count + 1));
   LoadingUnit& unit = LoadingUnit::Handle(zone);
   LoadingUnit& parent = LoadingUnit::Handle(zone);
   Library& lib = Library::Handle(zone);
+  Array& uris = Array::Handle(zone);
 
   for (int i = 0; i < unit_count; i++) {
     intptr_t id = helper_->ReadUInt();
@@ -1907,6 +1909,7 @@ void LoadingUnitsMetadataHelper::ReadMetadata(intptr_t node_offset) {
     unit.set_parent(parent);
 
     intptr_t library_count = helper_->ReadUInt();
+    uris = Array::New(library_count);
     for (intptr_t j = 0; j < library_count; j++) {
       const String& uri =
           translation_helper_.DartSymbolPlain(helper_->ReadStringReference());
@@ -1915,14 +1918,18 @@ void LoadingUnitsMetadataHelper::ReadMetadata(intptr_t node_offset) {
         FATAL1("Missing library: %s\n", uri.ToCString());
       }
       lib.set_loading_unit(unit);
+      uris.SetAt(j, uri);
     }
 
     loading_units.SetAt(id, unit);
+    loading_unit_uris.SetAt(id, uris);
   }
 
   ObjectStore* object_store = IG->object_store();
   ASSERT(object_store->loading_units() == Array::null());
   object_store->set_loading_units(loading_units);
+  ASSERT(object_store->loading_unit_uris() == Array::null());
+  object_store->set_loading_unit_uris(loading_unit_uris);
 }
 
 CallSiteAttributesMetadataHelper::CallSiteAttributesMetadataHelper(
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 4f03fb7a8a75..f8b05d203a6f 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -6728,24 +6728,12 @@ DART_EXPORT Dart_Handle Dart_LoadingUnitLibraryUris(intptr_t loading_unit_id) {
   DARTSCOPE(Thread::Current());
   API_TIMELINE_DURATION(T);
 
-  const GrowableObjectArray& result =
-      GrowableObjectArray::Handle(Z, GrowableObjectArray::New());
-  const GrowableObjectArray& libs = GrowableObjectArray::Handle(
-      Z, T->isolate_group()->object_store()->libraries());
-  Library& lib = Library::Handle(Z);
-  LoadingUnit& unit = LoadingUnit::Handle(Z);
-  String& uri = String::Handle(Z);
-  for (intptr_t i = 0; i < libs.Length(); i++) {
-    lib ^= libs.At(i);
-    unit = lib.loading_unit();
-    if (unit.IsNull() || (unit.id() != loading_unit_id)) {
-      continue;
-    }
-    uri = lib.url();
-    result.Add(uri);
+  const Array& loading_units =
+      Array::Handle(Z, T->isolate_group()->object_store()->loading_unit_uris());
+  if (loading_unit_id >= 0 && loading_unit_id < loading_units.Length()) {
+    return Api::NewHandle(T, loading_units.At(loading_unit_id));
   }
-
-  return Api::NewHandle(T, Array::MakeFixedLength(result));
+  return Api::NewError("Invalid loading_unit_id");
 #endif
 }
 
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index deae3104f6cb..0b5f8bc69282 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -12452,8 +12452,12 @@ void Library::set_name(const String& name) const {
   untag()->set_name(name.ptr());
 }
 
-void Library::set_url(const String& name) const {
-  untag()->set_url(name.ptr());
+void Library::set_url(const String& url) const {
+  untag()->set_url(url.ptr());
+}
+
+void Library::set_private_key(const String& key) const {
+  untag()->set_private_key(key.ptr());
 }
 
 void Library::set_kernel_data(const ExternalTypedData& data) const {
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 6f226c376e2a..dd1699a81700 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -5109,6 +5109,7 @@ class Library : public Object {
   // the name and url.
   void set_name(const String& name) const;
   void set_url(const String& url) const;
+  void set_private_key(const String& key) const;
 
   void set_num_imports(intptr_t value) const;
   void set_flags(uint8_t flags) const;
diff --git a/runtime/vm/object_store.h b/runtime/vm/object_store.h
index 674d1b4180fe..718e61d8471a 100644
--- a/runtime/vm/object_store.h
+++ b/runtime/vm/object_store.h
@@ -261,6 +261,7 @@ class ObjectPointerVisitor;
   RW(Array, dispatch_table_code_entries)                                       \
   RW(GrowableObjectArray, instructions_tables)                                 \
   RW(Array, obfuscation_map)                                                   \
+  RW(Array, loading_unit_uris)                                                 \
   RW(GrowableObjectArray, ffi_callback_functions)                              \
   RW(Class, ffi_pointer_class)                                                 \
   RW(Class, ffi_native_type_class)                                             \
diff --git a/sdk/lib/_internal/vm/bin/socket_patch.dart b/sdk/lib/_internal/vm/bin/socket_patch.dart
index d0bddf85fbfc..a70896e9f0f1 100644
--- a/sdk/lib/_internal/vm/bin/socket_patch.dart
+++ b/sdk/lib/_internal/vm/bin/socket_patch.dart
@@ -2543,6 +2543,7 @@ Datagram _makeDatagram(
 }
 
 @patch
+@pragma("vm:entry-point")
 class ResourceHandle {
   factory ResourceHandle.fromFile(RandomAccessFile file) {
     int fd = (file as _RandomAccessFile).fd;