Whenever possible use length passed to the List constructor for bounds checks instead of loading it…

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 069528f16caff523eacd1fd4959aad9043416f87..10292764b10394e5f6bf687ca695fda55bd1953c 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -1125,6 +1125,11 @@ RawAbstractType* CheckArrayBoundInstr::CompileType() const {
 }
 
 
+RawAbstractType* CheckBoundInstr::CompileType() const {
+  return AbstractType::null();
+}
+
+
 RawAbstractType* CheckEitherNonSmiInstr::CompileType() const {
   return AbstractType::null();
 }
@@ -1181,6 +1186,28 @@ Definition* CheckEitherNonSmiInstr::Canonicalize() {
 }
 
 
+Definition* CheckArrayBoundInstr::Canonicalize() {
+  if (array_type() == kArrayCid) {
+    // For fixed length arrays check if array is the result of a constructor
+    // call. In this case we can use the length passed to the constructor
+    // instead of loading it from array itself.
+    StaticCallInstr* allocation = array()->definition()->AsStaticCall();
+    if ((allocation != NULL) &&
+        allocation->is_known_constructor() &&
+        (allocation->ResultCid() == kArrayCid)) {
+      CheckBoundInstr* check =
+          new CheckBoundInstr(allocation->ArgumentAt(0)->value()->Copy(),
+                              index(),
+                              deopt_id_);
+      check->set_env(env());
+      set_env(NULL);
+      return check;
+    }
+  }
+  return this;
+}
+
+
 // Shared code generation methods (EmitNativeCode, MakeLocationSummary, and
 // PrepareEntry). Only assembly code that can be shared across all architectures
 // can be used. Machine specific register allocation and code generation