Eliminate bounds checks on fixed-length registers array.

runtime/vm/regexp_assembler.cc

 // Copyright (c) 2014, 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/regexp_assembler.h"
 
 #include "vm/bit_vector.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 181 matching lines @@
   StoreLocal(current_position_, Bind(Sub(start_index_push, length_push)));
 
   // Generate a local list variable to represent "registers" and
   // initialize capture registers (others remain garbage).
   StoreLocal(registers_, Bind(new(I) ConstantInstr(registers_array_)));
   ClearRegisters(0, saved_registers_count_ - 1);
 
   // Generate a local list variable to represent the backtracking stack.
   StoreLocal(stack_, Bind(new(I) ConstantInstr(stack_array_)));
   PushArgumentInstr* stack_push = PushLocal(stack_);
-  Do(InstanceCall(InstanceCallDescriptor(Symbols::clear()), stack_push));
+  PushArgumentInstr* zero_push = PushArgument(Bind(Uint64Constant(0)));
+  Do(InstanceCall(InstanceCallDescriptor(
+      Library::PrivateCoreLibName(Symbols::_setLength())),
+      stack_push,
+      zero_push));
 
   // Jump to the start block.
   current_instruction_->Goto(start_block_);
 }
 
 
 void IRRegExpMacroAssembler::GenerateBacktrackBlock() {
   set_current_instruction(backtrack_block_);
   TAG();
   CheckPreemption();
@@ skipping 1648 matching lines @@
       index_val,
       characters,
       specialization_cid_,
       Scanner::kNoSourcePos));
 }
 
 
 #undef __
 
 }  // namespace dart