Eliminate bounds checks on fixed-length registers array.

runtime/vm/constant_propagator.cc

Index: runtime/vm/constant_propagator.cc
diff --git a/runtime/vm/constant_propagator.cc b/runtime/vm/constant_propagator.cc
index efff680f2b5d194e4f052b32f35a7636f0752655..0c765f273b9d43b8797365a94a9d8e5f9bae281c 100644
--- a/runtime/vm/constant_propagator.cc
+++ b/runtime/vm/constant_propagator.cc
@@ -803,6 +803,11 @@ void ConstantPropagator::VisitLoadField(LoadFieldInstr* instr) {
             Smi::New(Array::Cast(constant->value()).Length())));
         return;
       }
+      if (constant->value().IsTypedData()) {
+        SetValue(instr, Smi::ZoneHandle(I,
+            Smi::New(TypedData::Cast(constant->value()).Length())));
+        return;
+      }
     }
   }
   SetValue(instr, non_constant_);