Avoid array bounds check when allowed by guarded field.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 752 matching lines @@
                                               Definition** array,
                                               Definition** index) {
   // Insert class check and index smi checks and attach a copy of the
   // original environment because the operation can still deoptimize.
   AddReceiverCheck(call);
   InsertBefore(call,
                new CheckSmiInstr(new Value(*index), call->deopt_id()),
                call->env(),
                Definition::kEffect);
 
+  // Get the field if the array is loaded from a class field.
+  const Field* field = NULL;
+  if ((*array)->IsLoadField()) {
+    LoadFieldInstr* load_field_instr = (*array)->AsLoadField();
+    field = load_field_instr->field();
+  }
+
   // Insert array length load and bounds check.
   const bool is_immutable =
       CheckArrayBoundInstr::IsFixedLengthArrayType(class_id);
   LoadFieldInstr* length =
       new LoadFieldInstr(new Value(*array),
                          CheckArrayBoundInstr::LengthOffsetFor(class_id),
                          Type::ZoneHandle(Type::SmiType()),
                          is_immutable);
   length->set_result_cid(kSmiCid);
   length->set_recognized_kind(
       LoadFieldInstr::RecognizedKindFromArrayCid(class_id));
   InsertBefore(call, length, NULL, Definition::kValue);
   InsertBefore(call,
-               new CheckArrayBoundInstr(new Value(length),
+               new CheckArrayBoundInstr(field,
+                                        new Value(length),
                                         new Value(*index),
                                         call->deopt_id()),
                call->env(),
                Definition::kEffect);
 
   if (class_id == kGrowableObjectArrayCid) {
     // Insert data elements load.
     LoadFieldInstr* elements =
         new LoadFieldInstr(new Value(*array),
                            GrowableObjectArray::data_offset(),
@@ skipping 884 matching lines @@
         String::Cast(str->AsConstant()->value());
     const Object& constant_index = index->AsConstant()->value();
     skip_check = constant_index.IsSmi() &&
         (Smi::Cast(constant_index).Value() < constant_string.Length());
   }
   if (!skip_check) {
     // Insert bounds check.
     LoadFieldInstr* length = BuildLoadStringLength(str);
     InsertBefore(call, length, NULL, Definition::kValue);
     InsertBefore(call,
-                 new CheckArrayBoundInstr(new Value(length),
+                 new CheckArrayBoundInstr(NULL,
+                                          new Value(length),
                                           new Value(index),
                                           call->deopt_id()),
                  call->env(),
                  Definition::kEffect);
   }
   return new LoadIndexedInstr(new Value(str),
                               new Value(index),
                               FlowGraphCompiler::ElementSizeFor(cid),
                               cid,
                               Isolate::kNoDeoptId);  // Can't deoptimize.
@@ skipping 752 matching lines @@
       flow_graph()->GetConstant(Smi::Handle(Smi::New(element_size)));
   BinarySmiOpInstr* len_in_bytes =
       new BinarySmiOpInstr(Token::kMUL,
                            new Value(length),
                            new Value(bytes_per_element),
                            call->deopt_id());
   InsertBefore(call, len_in_bytes, call->env(), Definition::kValue);
 
     // Check byte_index < len_in_bytes.
   InsertBefore(call,
-               new CheckArrayBoundInstr(new Value(len_in_bytes),
+               new CheckArrayBoundInstr(NULL,
+                                        new Value(len_in_bytes),
                                         new Value(byte_index),
                                         call->deopt_id()),
                call->env(),
                Definition::kEffect);
 
   // Insert load of elements for external typed arrays.
   if (RawObject::IsExternalTypedDataClassId(receiver_cid)) {
     LoadUntaggedInstr* elements =
         new LoadUntaggedInstr(new Value(*array),
                               ExternalTypedData::data_offset());
@@ skipping 5032 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart