[async-await] (simpler) fix for Return in try/finally in async functions

src/ast/scopes.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_SCOPES_H_
 #define V8_AST_SCOPES_H_
 
 #include "src/base/compiler-specific.h"
 #include "src/base/hashmap.h"
 #include "src/globals.h"
@@ skipping 662 matching lines @@
   // Declare the function variable for a function literal. This variable
   // is in an intermediate scope between this function scope and the the
   // outer scope. Only possible for function scopes; at most one variable.
   //
   // This function needs to be called after all other variables have been
   // declared in the scope. It will add a variable for {name} to {variables_};
   // either the function variable itself, or a non-local in case the function
   // calls sloppy eval.
   Variable* DeclareFunctionVar(const AstRawString* name);
 
+  // Declare some special internal variables which must be accessible to
+  // Ignition without ScopeInfo.
+  Variable* DeclareGeneratorObjectVar(const AstRawString* name);
+  Variable* DeclarePromiseVar(const AstRawString* name);
+
   // Declare a parameter in this scope.  When there are duplicated
   // parameters the rightmost one 'wins'.  However, the implementation
   // expects all parameters to be declared and from left to right.
   Variable* DeclareParameter(const AstRawString* name, VariableMode mode,
                              bool is_optional, bool is_rest, bool* is_duplicate,
                              AstValueFactory* ast_value_factory);
 
   // Declare an implicit global variable in this scope which must be a
   // script scope.  The variable was introduced (possibly from an inner
   // scope) by a reference to an unresolved variable with no intervening
@@ skipping 18 matching lines @@
   // The variable corresponding to the 'new.target' value.
   Variable* new_target_var() { return new_target_; }
 
   // The variable holding the function literal for named function
   // literals, or NULL.  Only valid for function scopes.
   Variable* function_var() const {
     DCHECK(is_function_scope());
     return function_;
   }
 
+  Variable* generator_object_var() const {
+    DCHECK(is_function_scope() || is_module_scope());
+    return GetRareVariable(RareVariable::kGeneratorObject);
+  }
+
+  Variable* promise_var() const {
+    DCHECK(is_function_scope());
+    DCHECK(IsAsyncFunction(function_kind_));
+    return GetRareVariable(RareVariable::kPromise);
+  }
+
   // Parameters. The left-most parameter has index 0.
   // Only valid for function and module scopes.
   Variable* parameter(int index) const {
     DCHECK(is_function_scope() || is_module_scope());
     return params_[index];
   }
 
   // Returns the number of formal parameters, excluding a possible rest
   // parameter.  Examples:
   //   function foo(a, b) {}         ==> 2
@@ skipping 20 matching lines @@
     has_simple_parameters_ = false;
   }
 
   // The local variable 'arguments' if we need to allocate it; NULL otherwise.
   Variable* arguments() const {
     DCHECK(!is_arrow_scope() || arguments_ == nullptr);
     return arguments_;
   }
 
   Variable* this_function_var() const {
+    Variable* this_function = GetRareVariable(RareVariable::kThisFunction);
+
     // This is only used in derived constructors atm.
-    DCHECK(this_function_ == nullptr ||
+    DCHECK(this_function == nullptr ||
            (is_function_scope() && (IsClassConstructor(function_kind()) ||
                                     IsConciseMethod(function_kind()) ||
                                     IsAccessorFunction(function_kind()))));
-    return this_function_;
+    return this_function;
   }
 
   // Adds a local variable in this scope's locals list. This is for adjusting
   // the scope of temporaries and do-expression vars when desugaring parameter
   // initializers.
   void AddLocal(Variable* var);
 
   void DeclareSloppyBlockFunction(
       const AstRawString* name, Scope* scope,
       SloppyBlockFunctionStatement* statement = nullptr);
@@ skipping 88 matching lines @@
   // Map of function names to lists of functions defined in sloppy blocks
   SloppyBlockFunctionMap sloppy_block_function_map_;
   // Convenience variable.
   Variable* receiver_;
   // Function variable, if any; function scopes only.
   Variable* function_;
   // new.target variable, function scopes only.
   Variable* new_target_;
   // Convenience variable; function scopes only.
   Variable* arguments_;
-  // Convenience variable; Subclass constructor only
-  Variable* this_function_;
+
+  struct RareData : public ZoneObject {
+    void* operator new(size_t size, Zone* zone) { return zone->New(size); }

[caitp, 2017/02/10 09:38:23]

Okay, here's a "RareData" solution... it does potentially mean that the rare
data structure won't be close to the scope itself in its zone, but presumably
that could be changed by allocating it early based on function-kind.

+
+    // Convenience variable; Subclass constructor only
+    Variable* this_function = nullptr;
+
+    // Generator object, if any; generator function scopes and module scopes
+    // only.
+    Variable* generator_object = nullptr;
+    // Promise, if any; async function scopes only.
+    Variable* promise = nullptr;
+  };
+
+  enum class RareVariable {
+    kThisFunction = offsetof(RareData, this_function),
+    kGeneratorObject = offsetof(RareData, generator_object),
+    kPromise = offsetof(RareData, promise)
+  };
+
+  V8_INLINE RareData* EnsureRareData() {
+    if (rare_data_ == nullptr) {
+      rare_data_ = new (zone_) RareData;
+    }
+    return rare_data_;
+  }
+
+  V8_INLINE Variable* GetRareVariable(RareVariable id) const {
+    if (rare_data_ == nullptr) return nullptr;
+    return *reinterpret_cast<Variable**>(
+        reinterpret_cast<uint8_t*>(rare_data_) + static_cast<ptrdiff_t>(id));
+  }
+
+  // Set `var` to null if it's non-null and Predicate (Variable*) -> bool
+  // returns true.
+  template <typename Predicate>
+  V8_INLINE void NullifyRareVariableIf(RareVariable id, Predicate predicate) {
+    if (V8_LIKELY(rare_data_ == nullptr)) return;
+    Variable** var = reinterpret_cast<Variable**>(
+        reinterpret_cast<uint8_t*>(rare_data_) + static_cast<ptrdiff_t>(id));
+    if (*var && predicate(*var)) *var = nullptr;
+  }
+
+  RareData* rare_data_ = nullptr;
 };
 
 class ModuleScope final : public DeclarationScope {
  public:
   ModuleScope(DeclarationScope* script_scope,
               AstValueFactory* ast_value_factory);
 
   // Deserialization.
   // The generated ModuleDescriptor does not preserve all information.  In
   // particular, its module_requests map will be empty because we no longer need
@@ skipping 11 matching lines @@
   void AllocateModuleVariables();
 
  private:
   ModuleDescriptor* module_descriptor_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_SCOPES_H_