[turbofan] Fix assert caused by bogus merging of out-of-scope CodeAssembler variables

src/compiler/code-assembler.h

 // Copyright 2015 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_COMPILER_CODE_ASSEMBLER_H_
 #define V8_COMPILER_CODE_ASSEMBLER_H_
 
 #include <map>
 
 // Clients of this interface shouldn't depend on lots of compiler internals.
@@ skipping 148 matching lines @@
 
   bool Is64() const;
   bool IsFloat64RoundUpSupported() const;
   bool IsFloat64RoundDownSupported() const;
   bool IsFloat64RoundTruncateSupported() const;
 
   class Label;
   class Variable {
    public:
     explicit Variable(CodeAssembler* assembler, MachineRepresentation rep);
+    ~Variable();
     void Bind(Node* value);
     Node* value() const;
     MachineRepresentation rep() const;
     bool IsBound() const;
 
    private:
     friend class CodeAssembler;
     class Impl;
     Impl* impl_;
+    CodeAssembler* assembler_;
   };
 
   enum AllocationFlag : uint8_t {
     kNone = 0,
     kDoubleAlignment = 1,
     kPretenured = 1 << 1
   };
 
   typedef base::Flags<AllocationFlag> AllocationFlags;
 
@@ skipping 167 matching lines @@
   CodeAssembler(Isolate* isolate, Zone* zone, CallDescriptor* call_descriptor,
                 Code::Flags flags, const char* name);
 
   Node* CallN(CallDescriptor* descriptor, Node* code_target, Node** args);
   Node* TailCallN(CallDescriptor* descriptor, Node* code_target, Node** args);
 
   base::SmartPointer<RawMachineAssembler> raw_assembler_;
   Code::Flags flags_;
   const char* name_;
   bool code_generated_;
-  ZoneVector<Variable::Impl*> variables_;
+  ZoneSet<Variable::Impl*> variables_;
 
   DISALLOW_COPY_AND_ASSIGN(CodeAssembler);
 };
 
 DEFINE_OPERATORS_FOR_FLAGS(CodeAssembler::AllocationFlags);
 
 class CodeAssembler::Label {
  public:
   enum Type { kDeferred, kNonDeferred };
 
@@ skipping 25 matching lines @@
   // Map of variables to the list of value nodes that have been added from each
   // merge path in their order of merging.
   std::map<Variable::Impl*, std::vector<Node*>> variable_merges_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_ASSEMBLER_H_