Recognize pattern (a << b) & c with c being a positive Smi and allow left shift to truncate the res…

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 18705)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -3669,7 +3669,8 @@
                            Value* left,
                            Value* right,
                            InstanceCallInstr* instance_call)
-      : op_kind_(op_kind) {
+      : op_kind_(op_kind),
+        instance_call_(instance_call) {
     ASSERT(left != NULL);
     ASSERT(right != NULL);
     inputs_[0] = left;
@@ -3682,6 +3683,8 @@
 
   Token::Kind op_kind() const { return op_kind_; }
 
+  InstanceCallInstr* instance_call() const { return instance_call_; }
+
   virtual void PrintOperandsTo(BufferFormatter* f) const;
 
   virtual bool CanDeoptimize() const {
@@ -3693,6 +3696,7 @@
   virtual bool AffectedBySideEffect() const { return false; }
 
   virtual bool AttributesEqual(Instruction* other) const {
+    ASSERT(other->IsBinaryMintOp());
     return op_kind() == other->AsBinaryMintOp()->op_kind();
   }
 
@@ -3719,6 +3723,7 @@
 
  private:
   const Token::Kind op_kind_;
+  InstanceCallInstr* instance_call_;
 
   DISALLOW_COPY_AND_ASSIGN(BinaryMintOpInstr);
 };
@@ -3844,7 +3849,8 @@
                    Value* right)
       : op_kind_(op_kind),
         instance_call_(instance_call),
-        overflow_(true) {
+        overflow_(true),
+        is_truncating_(false) {
     ASSERT(left != NULL);
     ASSERT(right != NULL);
     inputs_[0] = left;
@@ -3878,6 +3884,11 @@
     overflow_ = overflow;
   }
 
+  void set_is_truncating(bool value) {
+    is_truncating_ = value;
+  }
+  bool is_truncating() const { return is_truncating_; }
+
   void PrintTo(BufferFormatter* f) const;
 
   virtual void InferRange();
@@ -3892,6 +3903,7 @@
   const Token::Kind op_kind_;
   InstanceCallInstr* instance_call_;
   bool overflow_;
+  bool is_truncating_;
 
   DISALLOW_COPY_AND_ASSIGN(BinarySmiOpInstr);
 };