Bisect clang

tools/clang/blink_gc_plugin/CheckTraceVisitor.cpp

+// Copyright 2015 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 "CheckTraceVisitor.h"
+
+#include <vector>
+
+#include "Config.h"
+
+using namespace clang;
+
+CheckTraceVisitor::CheckTraceVisitor(CXXMethodDecl* trace,
+                                     RecordInfo* info,
+                                     RecordCache* cache)
+    : trace_(trace),
+      info_(info),
+      cache_(cache),
+      delegates_to_traceimpl_(false) {
+}
+
+bool CheckTraceVisitor::delegates_to_traceimpl() const {
+  return delegates_to_traceimpl_;
+}
+
+bool CheckTraceVisitor::VisitMemberExpr(MemberExpr* member) {
+  // In weak callbacks, consider any occurrence as a correct usage.
+  // TODO: We really want to require that isAlive is checked on manually
+  // processed weak fields.
+  if (IsWeakCallback()) {
+    if (FieldDecl* field = dyn_cast<FieldDecl>(member->getMemberDecl()))
+      FoundField(field);
+  }
+  return true;
+}
+
+bool CheckTraceVisitor::VisitCallExpr(CallExpr* call) {
+  // In weak callbacks we don't check calls (see VisitMemberExpr).
+  if (IsWeakCallback())
+    return true;
+
+  Expr* callee = call->getCallee();
+
+  // Trace calls from a templated derived class result in a
+  // DependentScopeMemberExpr because the concrete trace call depends on the
+  // instantiation of any shared template parameters. In this case the call is
+  // "unresolved" and we resort to comparing the syntactic type names.
+  if (CXXDependentScopeMemberExpr* expr =
+      dyn_cast<CXXDependentScopeMemberExpr>(callee)) {
+    CheckCXXDependentScopeMemberExpr(call, expr);
+    return true;
+  }
+
+  // A tracing call will have either a |visitor| or a |m_field| argument.
+  // A registerWeakMembers call will have a |this| argument.
+  if (call->getNumArgs() != 1)
+    return true;
+  Expr* arg = call->getArg(0);
+
+  if (UnresolvedMemberExpr* expr = dyn_cast<UnresolvedMemberExpr>(callee)) {
+    // This could be a trace call of a base class, as explained in the
+    // comments of CheckTraceBaseCall().
+    if (CheckTraceBaseCall(call))
+      return true;
+
+    if (expr->getMemberName().getAsString() == kRegisterWeakMembersName)
+      MarkAllWeakMembersTraced();
+
+    QualType base = expr->getBaseType();
+    if (!base->isPointerType())
+      return true;
+    CXXRecordDecl* decl = base->getPointeeType()->getAsCXXRecordDecl();
+    if (decl)
+      CheckTraceFieldCall(expr->getMemberName().getAsString(), decl, arg);
+    if (Config::IsTraceImplName(expr->getMemberName().getAsString()))
+      delegates_to_traceimpl_ = true;
+    return true;
+  }
+
+  if (CXXMemberCallExpr* expr = dyn_cast<CXXMemberCallExpr>(call)) {
+    if (CheckTraceFieldMemberCall(expr) || CheckRegisterWeakMembers(expr))
+      return true;
+
+    if (Config::IsTraceImplName(expr->getMethodDecl()->getNameAsString())) {
+      delegates_to_traceimpl_ = true;
+      return true;
+    }
+  }
+
+  CheckTraceBaseCall(call);
+  return true;
+}
+
+bool CheckTraceVisitor::IsTraceCallName(const std::string& name) {
+  if (trace_->getName() == kTraceImplName)
+    return name == kTraceName;
+  if (trace_->getName() == kTraceAfterDispatchImplName)
+    return name == kTraceAfterDispatchName;
+  // Currently, a manually dispatched class cannot have mixin bases (having
+  // one would add a vtable which we explicitly check against). This means
+  // that we can only make calls to a trace method of the same name. Revisit
+  // this if our mixin/vtable assumption changes.
+  return name == trace_->getName();
+}
+
+CXXRecordDecl* CheckTraceVisitor::GetDependentTemplatedDecl(
+    CXXDependentScopeMemberExpr* expr) {
+  NestedNameSpecifier* qual = expr->getQualifier();
+  if (!qual)
+    return 0;
+
+  const Type* type = qual->getAsType();
+  if (!type)
+    return 0;
+
+  return RecordInfo::GetDependentTemplatedDecl(*type);
+}
+
+namespace {
+
+class FindFieldVisitor : public RecursiveASTVisitor<FindFieldVisitor> {
+ public:
+  FindFieldVisitor();
+  MemberExpr* member() const;
+  FieldDecl* field() const;
+  bool TraverseMemberExpr(MemberExpr* member);
+
+ private:
+  MemberExpr* member_;
+  FieldDecl* field_;
+};
+
+FindFieldVisitor::FindFieldVisitor()
+    : member_(0),
+      field_(0) {
+}
+
+MemberExpr* FindFieldVisitor::member() const {
+  return member_;
+}
+
+FieldDecl* FindFieldVisitor::field() const {
+  return field_;
+}
+
+bool FindFieldVisitor::TraverseMemberExpr(MemberExpr* member) {
+  if (FieldDecl* field = dyn_cast<FieldDecl>(member->getMemberDecl())) {
+    member_ = member;
+    field_ = field;
+    return false;
+  }
+  return true;
+}
+
+}  // namespace
+
+void CheckTraceVisitor::CheckCXXDependentScopeMemberExpr(
+    CallExpr* call,
+    CXXDependentScopeMemberExpr* expr) {
+  std::string fn_name = expr->getMember().getAsString();
+
+  // Check for VisitorDispatcher::trace(field) and
+  // VisitorDispatcher::registerWeakMembers.
+  if (!expr->isImplicitAccess()) {
+    if (DeclRefExpr* base_decl = dyn_cast<DeclRefExpr>(expr->getBase())) {
+      if (Config::IsVisitorDispatcherType(base_decl->getType())) {
+        if (call->getNumArgs() == 1 && fn_name == kTraceName) {
+          FindFieldVisitor finder;
+          finder.TraverseStmt(call->getArg(0));
+          if (finder.field())
+            FoundField(finder.field());
+
+          return;
+        } else if (call->getNumArgs() == 1 &&
+                   fn_name == kRegisterWeakMembersName) {
+          MarkAllWeakMembersTraced();
+        }
+      }
+    }
+  }
+
+  CXXRecordDecl* tmpl = GetDependentTemplatedDecl(expr);
+  if (!tmpl)
+    return;
+
+  // Check for Super<T>::trace(visitor)
+  if (call->getNumArgs() == 1 && IsTraceCallName(fn_name)) {
+    RecordInfo::Bases::iterator it = info_->GetBases().begin();
+    for (; it != info_->GetBases().end(); ++it) {
+      if (it->first->getName() == tmpl->getName())
+        it->second.MarkTraced();
+    }
+  }
+
+  // Check for TraceIfNeeded<T>::trace(visitor, &field)
+  if (call->getNumArgs() == 2 && fn_name == kTraceName &&
+      tmpl->getName() == kTraceIfNeededName) {
+    FindFieldVisitor finder;
+    finder.TraverseStmt(call->getArg(1));
+    if (finder.field())
+      FoundField(finder.field());
+  }
+}
+
+bool CheckTraceVisitor::CheckTraceBaseCall(CallExpr* call) {
+  // Checks for "Base::trace(visitor)"-like calls.
+
+  // Checking code for these two variables is shared among MemberExpr* case
+  // and UnresolvedMemberCase* case below.
+  //
+  // For example, if we've got "Base::trace(visitor)" as |call|,
+  // callee_record will be "Base", and func_name will be "trace".
+  CXXRecordDecl* callee_record = nullptr;
+  std::string func_name;
+
+  if (MemberExpr* callee = dyn_cast<MemberExpr>(call->getCallee())) {
+    if (!callee->hasQualifier())
+      return false;
+
+    FunctionDecl* trace_decl =
+        dyn_cast<FunctionDecl>(callee->getMemberDecl());
+    if (!trace_decl || !Config::IsTraceMethod(trace_decl))
+      return false;
+
+    const Type* type = callee->getQualifier()->getAsType();
+    if (!type)
+      return false;
+
+    callee_record = type->getAsCXXRecordDecl();
+    func_name = trace_decl->getName();
+  } else if (UnresolvedMemberExpr* callee =
+             dyn_cast<UnresolvedMemberExpr>(call->getCallee())) {
+    // Callee part may become unresolved if the type of the argument
+    // ("visitor") is a template parameter and the called function is
+    // overloaded (i.e. trace(Visitor*) and
+    // trace(InlinedGlobalMarkingVisitor)).
+    //
+    // Here, we try to find a function that looks like trace() from the
+    // candidate overloaded functions, and if we find one, we assume it is
+    // called here.
+
+    CXXMethodDecl* trace_decl = nullptr;
+    for (NamedDecl* named_decl : callee->decls()) {
+      if (CXXMethodDecl* method_decl = dyn_cast<CXXMethodDecl>(named_decl)) {
+        if (Config::IsTraceMethod(method_decl)) {
+          trace_decl = method_decl;
+          break;
+        }
+      }
+    }
+    if (!trace_decl)
+      return false;
+
+    // Check if the passed argument is named "visitor".
+    if (call->getNumArgs() != 1)
+      return false;
+    DeclRefExpr* arg = dyn_cast<DeclRefExpr>(call->getArg(0));
+    if (!arg || arg->getNameInfo().getAsString() != kVisitorVarName)
+      return false;
+
+    callee_record = trace_decl->getParent();
+    func_name = callee->getMemberName().getAsString();
+  }
+
+  if (!callee_record)
+    return false;
+
+  if (!IsTraceCallName(func_name))
+    return false;
+
+  for (auto& base : info_->GetBases()) {
+    // We want to deal with omitted trace() function in an intermediary
+    // class in the class hierarchy, e.g.:
+    //     class A : public GarbageCollected<A> { trace() { ... } };
+    //     class B : public A { /* No trace(); have nothing to trace. */ };
+    //     class C : public B { trace() { B::trace(visitor); } }
+    // where, B::trace() is actually A::trace(), and in some cases we get
+    // A as |callee_record| instead of B. We somehow need to mark B as
+    // traced if we find A::trace() call.
+    //
+    // To solve this, here we keep going up the class hierarchy as long as
+    // they are not required to have a trace method. The implementation is
+    // a simple DFS, where |base_records| represents the set of base classes
+    // we need to visit.
+
+    std::vector<CXXRecordDecl*> base_records;
+    base_records.push_back(base.first);
+
+    while (!base_records.empty()) {
+      CXXRecordDecl* base_record = base_records.back();
+      base_records.pop_back();
+
+      if (base_record == callee_record) {
+        // If we find a matching trace method, pretend the user has written
+        // a correct trace() method of the base; in the example above, we
+        // find A::trace() here and mark B as correctly traced.
+        base.second.MarkTraced();
+        return true;
+      }
+
+      if (RecordInfo* base_info = cache_->Lookup(base_record)) {
+        if (!base_info->RequiresTraceMethod()) {
+          // If this base class is not required to have a trace method, then
+          // the actual trace method may be defined in an ancestor.
+          for (auto& inner_base : base_info->GetBases())
+            base_records.push_back(inner_base.first);
+        }
+      }
+    }
+  }
+
+  return false;
+}
+
+bool CheckTraceVisitor::CheckTraceFieldMemberCall(CXXMemberCallExpr* call) {
+  return CheckTraceFieldCall(call->getMethodDecl()->getNameAsString(),
+                             call->getRecordDecl(),
+                             call->getArg(0));
+}
+
+bool CheckTraceVisitor::CheckTraceFieldCall(
+    const std::string& name,
+    CXXRecordDecl* callee,
+    Expr* arg) {
+  if (name != kTraceName || !Config::IsVisitor(callee->getName()))
+    return false;
+
+  FindFieldVisitor finder;
+  finder.TraverseStmt(arg);
+  if (finder.field())
+    FoundField(finder.field());
+
+  return true;
+}
+
+bool CheckTraceVisitor::CheckRegisterWeakMembers(CXXMemberCallExpr* call) {
+  CXXMethodDecl* fn = call->getMethodDecl();
+  if (fn->getName() != kRegisterWeakMembersName)
+    return false;
+
+  if (fn->isTemplateInstantiation()) {
+    const TemplateArgumentList& args =
+        *fn->getTemplateSpecializationInfo()->TemplateArguments;
+    // The second template argument is the callback method.
+    if (args.size() > 1 &&
+        args[1].getKind() == TemplateArgument::Declaration) {
+      if (FunctionDecl* callback =
+          dyn_cast<FunctionDecl>(args[1].getAsDecl())) {
+        if (callback->hasBody()) {
+          CheckTraceVisitor nested_visitor(nullptr, info_, nullptr);
+          nested_visitor.TraverseStmt(callback->getBody());
+        }
+      }
+    }
+  }
+  return true;
+}
+
+bool CheckTraceVisitor::IsWeakCallback() const {
+  return !trace_;
+}
+
+void CheckTraceVisitor::MarkTraced(RecordInfo::Fields::iterator it) {
+  // In a weak callback we can't mark strong fields as traced.
+  if (IsWeakCallback() && !it->second.edge()->IsWeakMember())
+    return;
+  it->second.MarkTraced();
+}
+
+void CheckTraceVisitor::FoundField(FieldDecl* field) {
+  if (Config::IsTemplateInstantiation(info_->record())) {
+    // Pointer equality on fields does not work for template instantiations.
+    // The trace method refers to fields of the template definition which
+    // are different from the instantiated fields that need to be traced.
+    const std::string& name = field->getNameAsString();
+    for (RecordInfo::Fields::iterator it = info_->GetFields().begin();
+         it != info_->GetFields().end();
+         ++it) {
+      if (it->first->getNameAsString() == name) {
+        MarkTraced(it);
+        break;
+      }
+    }
+  } else {
+    RecordInfo::Fields::iterator it = info_->GetFields().find(field);
+    if (it != info_->GetFields().end())
+      MarkTraced(it);
+  }
+}
+
+void CheckTraceVisitor::MarkAllWeakMembersTraced() {
+  // If we find a call to registerWeakMembers which is unresolved we
+  // unsoundly consider all weak members as traced.
+  // TODO: Find out how to validate weak member tracing for unresolved call.
+  for (auto& field : info_->GetFields()) {
+    if (field.second.edge()->IsWeakMember())
+      field.second.MarkTraced();
+  }
+}