Replace guarded list length field loads with constants

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);
 
-  bool emit_bounds_check = true;
   // Get the field for the array.
   const Field* field = NULL;
   if ((*array)->IsLoadField()) {
     LoadFieldInstr* load_field_instr = (*array)->AsLoadField();
     field = load_field_instr->field();
   }
-  // Extract the guarded array length.
-  intptr_t guarded_array_length = -1;
-  if (field != NULL) {
-    if (field->guarded_list_length() >= 0) {
-      guarded_array_length = field->guarded_list_length();
-    }
-  }
-  Definition* i = *index;
-  // Check if we can skip emitting the bounds check.
-  if (i->IsConstant() && guarded_array_length >= 0) {
-    ConstantInstr* constant = i->AsConstant();
-    ASSERT(constant != NULL);
-    intptr_t ci = Smi::Cast(constant->value()).Value();
-    if (ci < guarded_array_length) {
-      emit_bounds_check = false;
-    }
-  }
 
-  if (emit_bounds_check) {
-    // 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 Value(*index),
-                                          call->deopt_id()),
-                 call->env(),
-                 Definition::kEffect);
-  }
+  // Insert array length load and bounds check.
+  const bool is_immutable =
+      CheckArrayBoundInstr::IsFixedLengthArrayType(class_id);
+  LoadFieldInstr* length =

[Florian Schneider, 2013/08/27 12:51:34]

If the field has a guarded_list_length: could you maybe just replace the length
LoadFieldInstr with a ConstantInstr? I think this would simplify the code a bit.

+      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(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(),
                            Type::ZoneHandle(Type::DynamicType()));
     elements->set_result_cid(kArrayCid);
     InsertBefore(call, elements, NULL, Definition::kValue);
@@ skipping 881 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 5040 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