Apply Kevin's suggestions, make branch-compare generation more robust

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 600 matching lines @@
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StrictCompareComp);
 };
 
 
 class EqualityCompareComp : public ComparisonComp {
  public:
   EqualityCompareComp(intptr_t token_pos,
                       intptr_t try_index,
+                      Token::Kind kind,
                       Value* left,
                       Value* right)
-      : ComparisonComp(Token::kEQ, left, right),
+      : ComparisonComp(kind, left, right),
         token_pos_(token_pos),
         try_index_(try_index),
-        receiver_class_id_(kObject) {}
+        receiver_class_id_(kObject) {
+    ASSERT((kind == Token::kEQ) || (kind == Token::kNE));
+  }
 
   DECLARE_COMPUTATION(EqualityCompare)
 
   intptr_t token_pos() const { return token_pos_; }
   intptr_t try_index() const { return try_index_; }
 
   void set_receiver_class_id(intptr_t value) { receiver_class_id_ = value; }
   intptr_t receiver_class_id() const { return receiver_class_id_; }
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
@@ skipping 1118 matching lines @@
     ASSERT(!IsGraphEntry());
     ASSERT(!IsReturn());
     ASSERT(!IsBranch());
     ASSERT(!IsPhi());
     ASSERT(instr == NULL || !instr->IsBlockEntry());
     // TODO(fschneider): Also add Throw and ReThrow to the list of instructions
     // that do not have a successor. Currently, the graph builder will continue
     // to append instruction in case of a Throw inside an expression. This
     // condition should be handled in the graph builder
     next_ = instr;
-    if ((instr != NULL) && !instr->IsBlockEntry()) {
-      instr->set_previous(this);
-    }
   }
 
   // Normal instructions can have 0 (inside a block) or 1 (last instruction in
   // a block) successors. Branch instruction with >1 successors override this
   // function.
   virtual intptr_t SuccessorCount() const;
   virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
 
   void Goto(JoinEntryInstr* entry);
 
@@ skipping 741 matching lines @@
   const GrowableArray<BlockEntryInstr*>& block_order_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_