Simplify type argument instantiation cache lookup by introducing an array

runtime/vm/intermediate_language_mips.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/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 2140 matching lines @@
   // the type arguments.
   Label type_arguments_instantiated;
   const intptr_t len = type_arguments().Length();
   if (type_arguments().IsRawInstantiatedRaw(len)) {
     __ BranchEqual(instantiator_reg, reinterpret_cast<int32_t>(Object::null()),
                    &type_arguments_instantiated);
   }
 
   __ LoadObject(T2, type_arguments());
   __ lw(T2, FieldAddress(T2, TypeArguments::instantiations_offset()));
-  __ lw(T3, FieldAddress(T2, Array::length_offset()));
   __ AddImmediate(T2, Array::data_offset() - kHeapObjectTag);
-  __ sll(TMP, T3, 1);  // T3 is Smi.
-  __ addu(T3, T2, TMP);
+  // The instantiations cache is initialized with Object::zero_array() and is
+  // therefore guaranteed to contain kNoInstantiator. No length check needed.
   Label loop, found, slow_case;
   __ Bind(&loop);
-  __ BranchUnsignedGreaterEqual(T2, T3, &slow_case);
   __ lw(T1, Address(T2, 0 * kWordSize));  // Cached instantiator.
   __ beq(T1, T0, &found);
   __ BranchEqual(T1, Smi::RawValue(StubCode::kNoInstantiator), &slow_case);
   __ b(&loop);
   __ delay_slot()->addiu(T2, T2, Immediate(2 * kWordSize));
   __ Bind(&found);
   __ lw(T0, Address(T2, 1 * kWordSize));  // Cached instantiated args.
   __ b(&type_arguments_instantiated);
 
   __ Bind(&slow_case);
@@ skipping 1994 matching lines @@
   compiler->GenerateCall(token_pos(),
                          &label,
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS