Improve array bounds check elimination for growable lists.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 23667)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -6208,9 +6208,7 @@
  public:
   CheckArrayBoundInstr(Value* length,
                        Value* index,
-                       intptr_t array_type,
-                       InstanceCallInstr* instance_call)
-      : array_type_(array_type) {
+                       InstanceCallInstr* instance_call) {
     SetInputAt(kLengthPos, length);
     SetInputAt(kIndexPos, index);
     deopt_id_ = instance_call->deopt_id();
@@ -6219,8 +6217,6 @@
   Value* length() const { return inputs_[kLengthPos]; }
   Value* index() const { return inputs_[kIndexPos]; }
 
-  intptr_t array_type() const { return array_type_; }
-
   DECLARE_INSTRUCTION(CheckArrayBound)
 
   virtual intptr_t ArgumentCount() const { return 0; }
@@ -6239,7 +6235,7 @@
   virtual bool AllowsCSE() const { return true; }
   virtual EffectSet Effects() const { return EffectSet::None(); }
   virtual EffectSet Dependencies() const { return EffectSet::None(); }
-  virtual bool AttributesEqual(Instruction* other) const;
+  virtual bool AttributesEqual(Instruction* other) const { return true; }
 
   virtual bool MayThrow() const { return false; }
 
@@ -6249,7 +6245,6 @@
     kLengthPos = 0,
     kIndexPos = 1
   };
-  intptr_t array_type_;
 
   DISALLOW_COPY_AND_ASSIGN(CheckArrayBoundInstr);
 };