Fix a pair of flow graph construction issues.

runtime/vm/intermediate_language.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 1508 matching lines @@
         successor_(NULL) {
     ASSERT(exception_ != NULL);
   }
 
   DECLARE_INSTRUCTION(Throw)
 
   intptr_t token_index() const { return token_index_; }
   intptr_t try_index() const { return try_index_; }
   Value* exception() const { return exception_; }
 
-  // Parser can generate a throw within an expression tree.
-  virtual Instruction* StraightLineSuccessor() const {
-    return successor_;
-  }
+  // Parser can generate a throw within an expression tree.  We never
+  // add successor instructions to the graph.
+  virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
-    successor_ = instr;
   }
 
  private:
   const intptr_t token_index_;
   const intptr_t try_index_;
   Value* exception_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(ThrowInstr);
 };
@@ skipping 14 matching lines @@
     ASSERT(stack_trace_ != NULL);
   }
 
   DECLARE_INSTRUCTION(ReThrow)
 
   intptr_t token_index() const { return token_index_; }
   intptr_t try_index() const { return try_index_; }
   Value* exception() const { return exception_; }
   Value* stack_trace() const { return stack_trace_; }
 
-  // Parser can generate a rethrow within an expression tree.
+  // Parser can generate a rethrow within an expression tree.  We
+  // never add successor instructions to the graph.
   virtual Instruction* StraightLineSuccessor() const {
-    return successor_;
+    return NULL;
   }
   virtual void SetSuccessor(Instruction* instr) {
     ASSERT(successor_ == NULL);
-    successor_ = instr;
   }
 
  private:
   const intptr_t token_index_;
   const intptr_t try_index_;
   Value* exception_;
   Value* stack_trace_;
   Instruction* successor_;
 
   DISALLOW_COPY_AND_ASSIGN(ReThrowInstr);
@@ skipping 73 matching lines @@
   const GrowableArray<BlockEntryInstr*>& block_order_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_