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 18774)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -241,6 +241,10 @@
   Value* next_use() const { return next_use_; }
   void set_next_use(Value* next) { next_use_ = next; }
 
+  bool IsSingleUse() const {
+    return (next_use_ == NULL) && (previous_use_ == NULL);

[Florian Schneider, 2013/02/21 10:30:47]

We have env_use_list to keep track of environment uses, so checking if the
definition has exactly one input use (and no environment uses) can be done
using:

return next_use_ == NULL
    && previous_use_ == NULL
    && definition_->env_use_list() == NULL;

[Kevin Millikin (Google), 2013/02/21 12:44:35]

Drive by to the drive by.  I think it's more natural to just write:

return (definition()->input_use_list() == this) &&
  (next_use() == NULL) &&
  (definition()->env_use_list() == NULL);

Both your definition and the original answer true for use list nodes held in
instructions that have been removed from the graph, which just seems like a
strange behavior.

[srdjan, 2013/02/21 15:56:27]

We remove environment use list lazily in register allocator, i.e., env_use_list
is most of the time non-null.

+  }
+
   Instruction* instruction() const { return instruction_; }
   void set_instruction(Instruction* instruction) { instruction_ = instruction; }
 
@@ -3673,7 +3677,8 @@
                            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;
@@ -3686,6 +3691,8 @@
 
   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 {
@@ -3697,6 +3704,7 @@
   virtual bool AffectedBySideEffect() const { return false; }
 
   virtual bool AttributesEqual(Instruction* other) const {
+    ASSERT(other->IsBinaryMintOp());
     return op_kind() == other->AsBinaryMintOp()->op_kind();
   }
 
@@ -3723,6 +3731,7 @@
 
  private:
   const Token::Kind op_kind_;
+  InstanceCallInstr* instance_call_;
 
   DISALLOW_COPY_AND_ASSIGN(BinaryMintOpInstr);
 };
@@ -3848,7 +3857,8 @@
                    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;
@@ -3882,6 +3892,11 @@
     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();
@@ -3896,6 +3911,7 @@
   const Token::Kind op_kind_;
   InstanceCallInstr* instance_call_;
   bool overflow_;
+  bool is_truncating_;
 
   DISALLOW_COPY_AND_ASSIGN(BinarySmiOpInstr);
 };