Replace guarded list length field loads with constants

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
diff --git a/runtime/vm/flow_graph_optimizer.cc b/runtime/vm/flow_graph_optimizer.cc
index d301900c6182f698f606b26f2e2c880fa8712066..53f44506c69e60afd150f7d538e0eb263949024f 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -770,51 +770,24 @@ intptr_t FlowGraphOptimizer::PrepareIndexedOp(InstanceCallInstr* call,
                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 =
+      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);
 
 
   if (class_id == kGrowableObjectArrayCid) {