Background compiler should validate CHA decisions before committing the code.

runtime/vm/cha.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/cha.h"
 #include "vm/class_table.h"
 #include "vm/flags.h"
 #include "vm/freelist.h"
 #include "vm/object.h"
 #include "vm/raw_object.h"
 #include "vm/visitor.h"
 
 namespace dart {
 
-void CHA::AddToLeafClasses(const Class& cls) {
-  for (intptr_t i = 0; i < leaf_classes_.length(); i++) {
-    if (leaf_classes_[i]->raw() == cls.raw()) {
+void CHA::AddToGuardedClasses(const Class& cls, intptr_t subclass_count) {
+  for (intptr_t i = 0; i < guarded_classes_.length(); i++) {
+    if (guarded_classes_[i].cls->raw() == cls.raw()) {
       return;
     }
   }
-  leaf_classes_.Add(&Class::ZoneHandle(thread_->zone(), cls.raw()));
+  GuardedClassInfo info = {
+    &Class::ZoneHandle(thread_->zone(), cls.raw()),
+    subclass_count
+  };
+  guarded_classes_.Add(info);
+  return;
 }
 
 
+bool CHA::IsGuardedClass(intptr_t cid) const {
+  for (intptr_t i = 0; i < guarded_classes_.length(); ++i) {
+    if (guarded_classes_[i].cls->id() == cid) return true;
+  }
+  return false;
+}
+
+
 bool CHA::HasSubclasses(const Class& cls) {
   ASSERT(!cls.IsNull());
   ASSERT(cls.id() >= kInstanceCid);
   // Can't track dependencies for classes on the VM heap since those are
   // read-only.
   // TODO(fschneider): Enable tracking of CHA dependent code for VM heap
   // classes.
   if (cls.InVMHeap()) return true;
 
   if (cls.IsObjectClass()) {
@@ skipping 44 matching lines @@
   // Can't track dependencies for classes on the VM heap since those are
   // read-only.
   // TODO(fschneider): Enable tracking of CHA dependent code for VM heap
   // classes.
   if (cls.InVMHeap()) return true;
 
   return cls.is_implemented();
 }
 
 
-bool CHA::HasOverride(const Class& cls, const String& function_name) {
+static intptr_t CountFinalizedSubclasses(Thread* thread, const Class& cls) {
+  intptr_t count = 0;
+  const GrowableObjectArray& cls_direct_subclasses =
+      GrowableObjectArray::Handle(thread->zone(), cls.direct_subclasses());
+  if (cls_direct_subclasses.IsNull()) return count;
+  Class& direct_subclass = Class::Handle(thread->zone());
+  for (intptr_t i = 0; i < cls_direct_subclasses.Length(); i++) {
+    direct_subclass ^= cls_direct_subclasses.At(i);
+    // Unfinalized classes are treated as non-existent for CHA purposes,
+    // as that means that no instance of that class exists at runtime.
+    const bool is_finalized = direct_subclass.is_finalized();
+    if (is_finalized) count++;

[Florian Schneider, 2016/05/20 11:23:28]

else continue?

Non-finalized class can't have finalized subclasses.

[Vyacheslav Egorov (Google), 2016/05/20 11:31:21]

Done.

+    count += CountFinalizedSubclasses(thread, direct_subclass);
+  }
+  return count;
+}
+
+
+bool CHA::IsConsistentWithCurrentHierarchy() const {
+  for (intptr_t i = 0; i < guarded_classes_.length(); i++) {
+    const intptr_t subclass_count =
+        CountFinalizedSubclasses(thread_, *guarded_classes_[i].cls);
+    if (guarded_classes_[i].subclass_count != subclass_count) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
+bool CHA::HasOverride(const Class& cls,
+                      const String& function_name,
+                      intptr_t* subclasses_count) {
   // Can't track dependencies for classes on the VM heap since those are
   // read-only.
   // TODO(fschneider): Enable tracking of CHA dependent code for VM heap
   // classes.
   if (cls.InVMHeap()) return true;
 
   // Subclasses of Object are not tracked by CHA. Safely assume that overrides
   // exist.
   if (cls.IsObjectClass()) {
     return true;
   }
 
   const GrowableObjectArray& cls_direct_subclasses =
       GrowableObjectArray::Handle(thread_->zone(), cls.direct_subclasses());
   if (cls_direct_subclasses.IsNull()) {
     return false;
   }
   Class& direct_subclass = Class::Handle(thread_->zone());
   for (intptr_t i = 0; i < cls_direct_subclasses.Length(); i++) {
     direct_subclass ^= cls_direct_subclasses.At(i);
     // Unfinalized classes are treated as non-existent for CHA purposes,
     // as that means that no instance of that class exists at runtime.
-    if (direct_subclass.is_finalized() &&
+    const bool is_finalized = direct_subclass.is_finalized();
+    if (is_finalized &&
         (direct_subclass.LookupDynamicFunction(function_name) !=
          Function::null())) {
       return true;
     }
-    if (HasOverride(direct_subclass, function_name)) {
+    if (HasOverride(direct_subclass, function_name, subclasses_count)) {

[Florian Schneider, 2016/05/20 11:23:28]

Same here: No need to recurse if !is_finalized.

[Vyacheslav Egorov (Google), 2016/05/20 11:31:21]

Done.

       return true;
     }
+    if (is_finalized) {
+      (*subclasses_count)++;
+    }
   }
   return false;
 }
 
+
+void CHA::RegisterDependencies(const Code& code) const {
+  for (intptr_t i = 0; i < guarded_classes_.length(); ++i) {
+    guarded_classes_[i].cls->RegisterCHACode(code);
+  }
+}
+
+
 }  // namespace dart