root/tools/clang/blink_gc_plugin/RecordInfo.cpp

DEFINITIONS

1. base_paths_
2. GetTemplateArgs
3. IsHeapAllocatedCollection
4. IsGCBaseCallback
5. IsGCDerived
6. IsGCFinalized
7. IsTreeShared
8. IsGCMixin
9. IsGCAllocated
10. Lookup
11. IsStackAllocated
12. IsNonNewable
13. IsOnlyPlacementNewable
14. RequiresTraceMethod
15. GetTraceMethod
16. GetTraceDispatchMethod
17. GetFinalizeDispatchMethod
18. GetBases
19. InheritsNonPureTrace
20. InheritsNonVirtualTrace
21. IsConsideredAbstract
22. CollectBases
23. GetFields
24. CollectFields
25. DetermineTracingMethods
26. NeedsFinalization
27. NeedsTracing
28. CreateEdge

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "Config.h"
#include "RecordInfo.h"

using namespace clang;
using std::string;

RecordInfo::RecordInfo(CXXRecordDecl* record, RecordCache* cache)
    : cache_(cache),
      record_(record),
      name_(record->getName()),
      fields_need_tracing_(TracingStatus::Unknown()),
      bases_(0),
      fields_(0),
      is_stack_allocated_(kNotComputed),
      is_non_newable_(kNotComputed),
      is_only_placement_newable_(kNotComputed),
      determined_trace_methods_(false),
      trace_method_(0),
      trace_dispatch_method_(0),
      finalize_dispatch_method_(0),
      is_gc_derived_(false),
      base_paths_(0) {}

RecordInfo::~RecordInfo() {
  delete fields_;
  delete bases_;
  delete base_paths_;
}

// Get |count| number of template arguments. Returns false if there
// are fewer than |count| arguments or any of the arguments are not
// of a valid Type structure. If |count| is non-positive, all
// arguments are collected.
bool RecordInfo::GetTemplateArgs(size_t count, TemplateArgs* output_args) {
  ClassTemplateSpecializationDecl* tmpl =
      dyn_cast<ClassTemplateSpecializationDecl>(record_);
  if (!tmpl)
    return false;
  const TemplateArgumentList& args = tmpl->getTemplateArgs();
  if (args.size() < count)
    return false;
  if (count <= 0)
    count = args.size();
  for (unsigned i = 0; i < count; ++i) {
    TemplateArgument arg = args[i];
    if (arg.getKind() == TemplateArgument::Type && !arg.getAsType().isNull()) {
      output_args->push_back(arg.getAsType().getTypePtr());
    } else {
      return false;
    }
  }
  return true;
}

// Test if a record is a HeapAllocated collection.
bool RecordInfo::IsHeapAllocatedCollection() {
  if (!Config::IsGCCollection(name_) && !Config::IsWTFCollection(name_))
    return false;

  TemplateArgs args;
  if (GetTemplateArgs(0, &args)) {
    for (TemplateArgs::iterator it = args.begin(); it != args.end(); ++it) {
      if (CXXRecordDecl* decl = (*it)->getAsCXXRecordDecl())
        if (decl->getName() == kHeapAllocatorName)
          return true;
    }
  }

  return Config::IsGCCollection(name_);
}

static bool IsGCBaseCallback(const CXXBaseSpecifier* specifier,
                             CXXBasePath& path,
                             void* data) {
  if (CXXRecordDecl* record = specifier->getType()->getAsCXXRecordDecl())
    return Config::IsGCBase(record->getName());
  return false;
}

// Test if a record is derived from a garbage collected base.
bool RecordInfo::IsGCDerived() {
  // If already computed, return the known result.
  if (base_paths_)
    return is_gc_derived_;

  base_paths_ = new CXXBasePaths(true, true, false);

  if (!record_->hasDefinition())
    return false;

  // The base classes are not themselves considered garbage collected objects.
  if (Config::IsGCBase(name_))
    return false;

  // Walk the inheritance tree to find GC base classes.
  is_gc_derived_ = record_->lookupInBases(IsGCBaseCallback, 0, *base_paths_);
  return is_gc_derived_;
}

bool RecordInfo::IsGCFinalized() {
  if (!IsGCDerived())
    return false;
  for (CXXBasePaths::paths_iterator it = base_paths_->begin();
       it != base_paths_->end();
       ++it) {
    const CXXBasePathElement& elem = (*it)[it->size() - 1];
    CXXRecordDecl* base = elem.Base->getType()->getAsCXXRecordDecl();
    if (Config::IsGCFinalizedBase(base->getName()))
      return true;
  }
  return false;
}

bool RecordInfo::IsTreeShared() {
  if (Config::IsTreeSharedBase(name_))
    return true;
  if (!IsGCDerived())
    return false;
  for (CXXBasePaths::paths_iterator it = base_paths_->begin();
       it != base_paths_->end();
       ++it) {
    // TreeShared is an immediate base of GCFinalized.
    if (it->size() < 2) continue;
    const CXXBasePathElement& elem = (*it)[it->size() - 2];
    CXXRecordDecl* base = elem.Base->getType()->getAsCXXRecordDecl();
    if (Config::IsTreeSharedBase(base->getName()))
      return true;
  }
  return false;
}

// A GC mixin is a class that inherits from a GC mixin base and has
// has not yet been "mixed in" with another GC base class.
bool RecordInfo::IsGCMixin() {
  if (!IsGCDerived() || base_paths_->begin() == base_paths_->end())
    return false;
  // Get the last element of the first path.
  CXXBasePaths::paths_iterator it = base_paths_->begin();
  const CXXBasePathElement& elem = (*it)[it->size() - 1];
  CXXRecordDecl* base = elem.Base->getType()->getAsCXXRecordDecl();
  // If it is not a mixin base we are done.
  if (!Config::IsGCMixinBase(base->getName()))
    return false;
  // This is a mixin if there are no other paths to GC bases.
  return ++it == base_paths_->end();
}

// Test if a record is allocated on the managed heap.
bool RecordInfo::IsGCAllocated() {
  return IsGCDerived() || IsHeapAllocatedCollection();
}

RecordInfo* RecordCache::Lookup(CXXRecordDecl* record) {
  // Ignore classes annotated with the GC_PLUGIN_IGNORE macro.
  if (!record || Config::IsIgnoreAnnotated(record))
    return 0;
  Cache::iterator it = cache_.find(record);
  if (it != cache_.end())
    return &it->second;
  return &cache_.insert(std::make_pair(record, RecordInfo(record, this)))
              .first->second;
}

bool RecordInfo::IsStackAllocated() {
  if (is_stack_allocated_ == kNotComputed) {
    is_stack_allocated_ = kFalse;
    for (Bases::iterator it = GetBases().begin();
         it != GetBases().end();
         ++it) {
      if (it->second.info()->IsStackAllocated()) {
        is_stack_allocated_ = kTrue;
        return is_stack_allocated_;
      }
    }
    for (CXXRecordDecl::method_iterator it = record_->method_begin();
         it != record_->method_end();
         ++it) {
      if (it->getNameAsString() == kNewOperatorName &&
          it->isDeleted() &&
          Config::IsStackAnnotated(*it)) {
        is_stack_allocated_ = kTrue;
        return is_stack_allocated_;
      }
    }
  }
  return is_stack_allocated_;
}

bool RecordInfo::IsNonNewable() {
  if (is_non_newable_ == kNotComputed) {
    bool deleted = false;
    bool all_deleted = true;
    for (CXXRecordDecl::method_iterator it = record_->method_begin();
         it != record_->method_end();
         ++it) {
      if (it->getNameAsString() == kNewOperatorName) {
        deleted = it->isDeleted();
        all_deleted = all_deleted && deleted;
      }
    }
    is_non_newable_ = (deleted && all_deleted) ? kTrue : kFalse;
  }
  return is_non_newable_;
}

bool RecordInfo::IsOnlyPlacementNewable() {
  if (is_only_placement_newable_ == kNotComputed) {
    bool placement = false;
    bool new_deleted = false;
    for (CXXRecordDecl::method_iterator it = record_->method_begin();
         it != record_->method_end();
         ++it) {
      if (it->getNameAsString() == kNewOperatorName) {
        if (it->getNumParams() == 1) {
          new_deleted = it->isDeleted();
        } else if (it->getNumParams() == 2) {
          placement = !it->isDeleted();
        }
      }
    }
    is_only_placement_newable_ = (placement && new_deleted) ? kTrue : kFalse;
  }
  return is_only_placement_newable_;
}

// An object requires a tracing method if it has any fields that need tracing.
bool RecordInfo::RequiresTraceMethod() {
  if (IsStackAllocated())
    return false;
  GetFields();
  return fields_need_tracing_.IsNeeded();
}

// Get the actual tracing method (ie, can be traceAfterDispatch if there is a
// dispatch method).
CXXMethodDecl* RecordInfo::GetTraceMethod() {
  DetermineTracingMethods();
  return trace_method_;
}

// Get the static trace dispatch method.
CXXMethodDecl* RecordInfo::GetTraceDispatchMethod() {
  DetermineTracingMethods();
  return trace_dispatch_method_;
}

CXXMethodDecl* RecordInfo::GetFinalizeDispatchMethod() {
  DetermineTracingMethods();
  return finalize_dispatch_method_;
}

RecordInfo::Bases& RecordInfo::GetBases() {
  if (!bases_)
    bases_ = CollectBases();
  return *bases_;
}

bool RecordInfo::InheritsNonPureTrace() {
  if (CXXMethodDecl* trace = GetTraceMethod())
    return !trace->isPure();
  for (Bases::iterator it = GetBases().begin(); it != GetBases().end(); ++it) {
    if (it->second.info()->InheritsNonPureTrace())
      return true;
  }
  return false;
}

CXXMethodDecl* RecordInfo::InheritsNonVirtualTrace() {
  if (CXXMethodDecl* trace = GetTraceMethod())
    return trace->isVirtual() ? 0 : trace;
  for (Bases::iterator it = GetBases().begin(); it != GetBases().end(); ++it) {
    if (CXXMethodDecl* trace = it->second.info()->InheritsNonVirtualTrace())
      return trace;
  }
  return 0;
}

// A (non-virtual) class is considered abstract in Blink if it has
// no public constructors and no create methods.
bool RecordInfo::IsConsideredAbstract() {
  for (CXXRecordDecl::ctor_iterator it = record_->ctor_begin();
       it != record_->ctor_end();
       ++it) {
    if (!it->isCopyOrMoveConstructor() && it->getAccess() == AS_public)
      return false;
  }
  for (CXXRecordDecl::method_iterator it = record_->method_begin();
       it != record_->method_end();
       ++it) {
    if (it->getNameAsString() == kCreateName)
      return false;
  }
  return true;
}

RecordInfo::Bases* RecordInfo::CollectBases() {
  // Compute the collection locally to avoid inconsistent states.
  Bases* bases = new Bases;
  if (!record_->hasDefinition())
    return bases;
  for (CXXRecordDecl::base_class_iterator it = record_->bases_begin();
       it != record_->bases_end();
       ++it) {
    const CXXBaseSpecifier& spec = *it;
    RecordInfo* info = cache_->Lookup(spec.getType());
    if (!info)
      continue;
    CXXRecordDecl* base = info->record();
    TracingStatus status = info->InheritsNonPureTrace()
                               ? TracingStatus::Needed()
                               : TracingStatus::Unneeded();
    bases->insert(std::make_pair(base, BasePoint(spec, info, status)));
  }
  return bases;
}

RecordInfo::Fields& RecordInfo::GetFields() {
  if (!fields_)
    fields_ = CollectFields();
  return *fields_;
}

RecordInfo::Fields* RecordInfo::CollectFields() {
  // Compute the collection locally to avoid inconsistent states.
  Fields* fields = new Fields;
  if (!record_->hasDefinition())
    return fields;
  TracingStatus fields_status = TracingStatus::Unneeded();
  for (RecordDecl::field_iterator it = record_->field_begin();
       it != record_->field_end();
       ++it) {
    FieldDecl* field = *it;
    // Ignore fields annotated with the GC_PLUGIN_IGNORE macro.
    if (Config::IsIgnoreAnnotated(field))
      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)));
    }
  }
  fields_need_tracing_ = fields_status;
  return fields;
}

void RecordInfo::DetermineTracingMethods() {
  if (determined_trace_methods_)
    return;
  determined_trace_methods_ = true;
  if (Config::IsGCBase(name_))
    return;
  CXXMethodDecl* trace = 0;
  CXXMethodDecl* traceAfterDispatch = 0;
  bool isTraceAfterDispatch;
  for (CXXRecordDecl::method_iterator it = record_->method_begin();
       it != record_->method_end();
       ++it) {
    if (Config::IsTraceMethod(*it, &isTraceAfterDispatch)) {
      if (isTraceAfterDispatch) {
        traceAfterDispatch = *it;
      } else {
        trace = *it;
      }
    } else if (it->getNameAsString() == kFinalizeName) {
      finalize_dispatch_method_ = *it;
    }
  }
  if (traceAfterDispatch) {
    trace_method_ = traceAfterDispatch;
    trace_dispatch_method_ = trace;
  } else {
    // TODO: Can we never have a dispatch method called trace without the same
    // class defining a traceAfterDispatch method?
    trace_method_ = trace;
    trace_dispatch_method_ = 0;
  }
  if (trace_dispatch_method_ && finalize_dispatch_method_)
    return;
  // If this class does not define dispatching methods inherit them.
  for (Bases::iterator it = GetBases().begin(); it != GetBases().end(); ++it) {
    // TODO: Does it make sense to inherit multiple dispatch methods?
    if (CXXMethodDecl* dispatch = it->second.info()->GetTraceDispatchMethod()) {
      assert(!trace_dispatch_method_ && "Multiple trace dispatching methods");
      trace_dispatch_method_ = dispatch;
    }
    if (CXXMethodDecl* dispatch =
            it->second.info()->GetFinalizeDispatchMethod()) {
      assert(!finalize_dispatch_method_ &&
             "Multiple finalize dispatching methods");
      finalize_dispatch_method_ = dispatch;
    }
  }
}

// TODO: Add classes with a finalize() method that specialize FinalizerTrait.
bool RecordInfo::NeedsFinalization() {
  return record_->hasNonTrivialDestructor();
}

// A class needs tracing if:
// - it is allocated on the managed heap,
// - it is derived from a class that needs tracing, or
// - it contains fields that need tracing.
// TODO: Defining NeedsTracing based on whether a class defines a trace method
// (of the proper signature) over approximates too much. The use of transition
// types causes some classes to have trace methods without them needing to be
// traced.
TracingStatus RecordInfo::NeedsTracing(Edge::NeedsTracingOption option) {
  if (IsGCAllocated())
    return TracingStatus::Needed();

  if (IsStackAllocated())
    return TracingStatus::Unneeded();

  for (Bases::iterator it = GetBases().begin(); it != GetBases().end(); ++it) {
    if (it->second.info()->NeedsTracing(option).IsNeeded())
      return TracingStatus::Needed();
  }

  if (option == Edge::kRecursive)
    GetFields();

  return fields_need_tracing_;
}

Edge* RecordInfo::CreateEdge(const Type* type) {
  if (!type) {
    return 0;
  }

  if (type->isPointerType()) {
    if (Edge* ptr = CreateEdge(type->getPointeeType().getTypePtrOrNull()))
      return new RawPtr(ptr);
    return 0;
  }

  RecordInfo* info = cache_->Lookup(type);

  // If the type is neither a pointer or a C++ record we ignore it.
  if (!info) {
    return 0;
  }

  TemplateArgs args;

  if (Config::IsRawPtr(info->name()) && info->GetTemplateArgs(1, &args)) {
    if (Edge* ptr = CreateEdge(args[0]))
      return new RawPtr(ptr);
    return 0;
  }

  if (Config::IsRefPtr(info->name()) && info->GetTemplateArgs(1, &args)) {
    if (Edge* ptr = CreateEdge(args[0]))
      return new RefPtr(ptr);
    return 0;
  }

  if (Config::IsOwnPtr(info->name()) && info->GetTemplateArgs(1, &args)) {
    if (Edge* ptr = CreateEdge(args[0]))
      return new OwnPtr(ptr);
    return 0;
  }

  if (Config::IsMember(info->name()) && info->GetTemplateArgs(1, &args)) {
    if (Edge* ptr = CreateEdge(args[0]))
      return new Member(ptr);
    return 0;
  }

  if (Config::IsWeakMember(info->name()) && info->GetTemplateArgs(1, &args)) {
    if (Edge* ptr = CreateEdge(args[0]))
      return new WeakMember(ptr);
    return 0;
  }

  if (Config::IsPersistent(info->name())) {
    // Persistent might refer to v8::Persistent, so check the name space.
    // TODO: Consider using a more canonical identification than names.
    NamespaceDecl* ns =
        dyn_cast<NamespaceDecl>(info->record()->getDeclContext());
    if (!ns || ns->getName() != "WebCore")
      return 0;
    if (!info->GetTemplateArgs(1, &args))
      return 0;
    if (Edge* ptr = CreateEdge(args[0]))
      return new Persistent(ptr);
    return 0;
  }

  if (Config::IsGCCollection(info->name()) ||
      Config::IsWTFCollection(info->name())) {
    bool is_root = Config::IsPersistentGCCollection(info->name());
    bool on_heap = is_root || info->IsHeapAllocatedCollection();
    size_t count = Config::CollectionDimension(info->name());
    if (!info->GetTemplateArgs(count, &args))
      return 0;
    Collection* edge = new Collection(info, on_heap, is_root);
    for (TemplateArgs::iterator it = args.begin(); it != args.end(); ++it) {
      if (Edge* member = CreateEdge(*it)) {
        edge->members().push_back(member);
      } else {
        // We failed to create an edge so abort the entire edge construction.
        delete edge;  // Will delete the already allocated members.
        return 0;
      }
    }
    return edge;
  }

  return new Value(info);
}