- Canonicalize array bounds checks to avoid deopting when comparing

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
===================================================================
--- runtime/vm/intermediate_language.h	(revision 22689)
+++ runtime/vm/intermediate_language.h	(working copy)
@@ -6152,13 +6152,13 @@
                        intptr_t array_type,
                        InstanceCallInstr* instance_call)
       : array_type_(array_type) {
-    SetInputAt(0, length);
-    SetInputAt(1, index);
+    SetInputAt(locLength, length);
+    SetInputAt(locIndex, index);
     deopt_id_ = instance_call->deopt_id();
   }
 
-  Value* length() const { return inputs_[0]; }
-  Value* index() const { return inputs_[1]; }
+  Value* length() const { return inputs_[locLength]; }
+  Value* index() const { return inputs_[locIndex]; }
 
   intptr_t array_type() const { return array_type_; }
 
@@ -6170,6 +6170,8 @@
 
   bool IsRedundant(RangeBoundary length);
 
+  virtual Instruction* Canonicalize(FlowGraph* flow_graph);
+
   // Returns the length offset for array and string types.
   static intptr_t LengthOffsetFor(intptr_t class_id);
 
@@ -6183,6 +6185,11 @@
   virtual bool MayThrow() const { return false; }
 
  private:
+  // Give a name to the location/input indices.
+  enum {
+    locLength = 0,
+    locIndex = 1

[srdjan, 2013/05/14 18:11:47]

Optional: prefix constant with k, call it kLengthPos and kIndexPos.

[Ivan Posva, 2013/05/14 18:30:30]

Done + simplified the code where we use the length and index location repeatedly
during code gen.

+  };
   intptr_t array_type_;
 
   DISALLOW_COPY_AND_ASSIGN(CheckArrayBoundInstr);