Simplify type argument instantiation cache lookup by introducing an array

runtime/vm/intermediate_language_ia32.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_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 2168 matching lines @@
     const Immediate& raw_null =
         Immediate(reinterpret_cast<intptr_t>(Object::null()));
     __ cmpl(instantiator_reg, raw_null);
     __ j(EQUAL, &type_arguments_instantiated, Assembler::kNearJump);
   }
   // Lookup cache before calling runtime.
   // TODO(fschneider): Consider moving this into a shared stub to reduce
   // generated code size.
   __ LoadObject(EDI, type_arguments());
   __ movl(EDI, FieldAddress(EDI, TypeArguments::instantiations_offset()));
-  __ movl(EBX, FieldAddress(EDI, Array::length_offset()));
   __ leal(EDI, FieldAddress(EDI, Array::data_offset()));
-  __ leal(EBX, Address(EDI, EBX, TIMES_2, 0));  // EBX is smi.
+  // 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);
-  __ cmpl(EDI, EBX);
-  __ j(ABOVE_EQUAL, &slow_case);
   __ movl(EDX, Address(EDI, 0 * kWordSize));  // Cached instantiator.
   __ cmpl(EDX, EAX);
   __ j(EQUAL, &found, Assembler::kNearJump);
   __ cmpl(EDX, Immediate(Smi::RawValue(StubCode::kNoInstantiator)));
   __ j(EQUAL, &slow_case);
   __ addl(EDI, Immediate(2 * kWordSize));

[Florian Schneider, 2014/02/17 10:09:59]

You could save one branch instruction by reordering the code like this:

__ addl(EDI, Immediate(2 * kWordSize));
__ cmpl(EDX, Immediate(Smi::RawValue(StubCode::kNoInstantiator)));
__ j(NOT_EQUAL, &loop);


This should work on all platforms.

[regis, 2014/02/18 19:29:29]

Done on all platforms.

   __ jmp(&loop, Assembler::kNearJump);
   __ Bind(&found);
   __ movl(EAX, Address(EDI, 1 * kWordSize));  // Cached instantiated args.
   __ jmp(&type_arguments_instantiated);
 
   __ Bind(&slow_case);
   // Instantiate non-null type arguments.
   // A runtime call to instantiate the type arguments is required.
   __ PushObject(Object::ZoneHandle());  // Make room for the result.
   __ PushObject(type_arguments());
@@ skipping 3065 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_IA32