blink_gc_plugin: Make RecordInfo::Get{Fields,Bases} return deterministic order

tools/clang/blink_gc_plugin/RecordInfo.cpp

Index: tools/clang/blink_gc_plugin/RecordInfo.cpp
diff --git a/tools/clang/blink_gc_plugin/RecordInfo.cpp b/tools/clang/blink_gc_plugin/RecordInfo.cpp
index 3c166dd4c431374f32ff2851d01654c82d7a805a..5d3aa4776abf2d73bd1c71defe6b39499d50e961 100644
--- a/tools/clang/blink_gc_plugin/RecordInfo.cpp
+++ b/tools/clang/blink_gc_plugin/RecordInfo.cpp
@@ -15,6 +15,7 @@ RecordInfo::RecordInfo(CXXRecordDecl* record, RecordCache* cache)
       fields_need_tracing_(TracingStatus::Unknown()),
       bases_(0),
       fields_(0),
+      field_map_(0),
       is_stack_allocated_(kNotComputed),
       is_non_newable_(kNotComputed),
       is_only_placement_newable_(kNotComputed),
@@ -30,6 +31,7 @@ RecordInfo::RecordInfo(CXXRecordDecl* record, RecordCache* cache)
 
 RecordInfo::~RecordInfo() {
   delete fields_;
+  delete field_map_;
   delete bases_;
 }
 
@@ -319,7 +321,7 @@ CXXMethodDecl* RecordInfo::GetFinalizeDispatchMethod() {
 
 RecordInfo::Bases& RecordInfo::GetBases() {
   if (!bases_)
-    bases_ = CollectBases();
+    CollectBases();
   return *bases_;
 }
 
@@ -383,11 +385,12 @@ bool RecordInfo::IsConsideredAbstract() {
   return true;
 }
 
-RecordInfo::Bases* RecordInfo::CollectBases() {
+void RecordInfo::CollectBases() {
   // Compute the collection locally to avoid inconsistent states.
-  Bases* bases = new Bases;
+  assert(!bases_);
+  bases_ = new Bases;
   if (!record_->hasDefinition())
-    return bases;
+    return;
   for (CXXRecordDecl::base_class_iterator it = record_->bases_begin();
        it != record_->bases_end();
        ++it) {
@@ -399,22 +402,38 @@ RecordInfo::Bases* RecordInfo::CollectBases() {
     TracingStatus status = info->InheritsTrace()
                                ? TracingStatus::Needed()
                                : TracingStatus::Unneeded();
-    bases->insert(std::make_pair(base, BasePoint(spec, info, status)));
+    bases_->push_back(std::make_pair(base, BasePoint(spec, info, status)));
   }
-  return bases;
 }
 
 RecordInfo::Fields& RecordInfo::GetFields() {
-  if (!fields_)
-    fields_ = CollectFields();
+  if (!fields_) {
+    assert(!field_map_);
+    CollectFields();
+  }
   return *fields_;
 }
 
-RecordInfo::Fields* RecordInfo::CollectFields() {
+bool RecordInfo::HasField(clang::FieldDecl* field) {
+  GetFields();
+  assert(field_map_);
+  return field_map_->count(field);
+}
+
+RecordInfo::Field& RecordInfo::GetField(clang::FieldDecl* field) {
+  assert(HasField(field));
+  return fields_->at((*field_map_)[field]);
+}
+
+void RecordInfo::CollectFields() {
   // Compute the collection locally to avoid inconsistent states.
-  Fields* fields = new Fields;
+  assert(!fields_);
+  fields_ = new Fields;
+  field_map_ = new std::map<clang::FieldDecl*, size_t>;
+
   if (!record_->hasDefinition())
-    return fields;
+    return;
+
   TracingStatus fields_status = TracingStatus::Unneeded();
   for (RecordDecl::field_iterator it = record_->field_begin();
        it != record_->field_end();
@@ -425,11 +444,11 @@ RecordInfo::Fields* RecordInfo::CollectFields() {
       continue;
     if (Edge* edge = CreateEdge(field->getType().getTypePtrOrNull())) {
       fields_status = fields_status.LUB(edge->NeedsTracing(Edge::kRecursive));
-      fields->insert(std::make_pair(field, FieldPoint(field, edge)));
+      (*field_map_)[field] = fields_->size();
+      fields_->push_back(std::make_pair(field, FieldPoint(field, edge)));
     }
   }
   fields_need_tracing_ = fields_status;
-  return fields;
 }
 
 void RecordInfo::DetermineTracingMethods() {