Uses a conditional move for usage counter increment instead of a branch

runtime/vm/stub_code_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"
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 1384 matching lines @@
   __ popl(ECX);  // Restore IC data array.
   __ popl(EDX);  // Restore arguments descriptor array.
   __ LeaveFrame();
   Label call_target_function;
   __ jmp(&call_target_function);
 
   __ Bind(&found);
   // EBX: Pointer to an IC data check group.
   const intptr_t target_offset = ICData::TargetIndexFor(num_args) * kWordSize;
   const intptr_t count_offset = ICData::CountIndexFor(num_args) * kWordSize;
+
+  // Update counter.
+  __ movl(EAX, Address(EBX, count_offset));
+  __ addl(EAX, Immediate(Smi::RawValue(1)));
+  __ movl(EDI, Immediate(Smi::RawValue(Smi::kMaxValue)));
+  __ cmovno(EDI, EAX);
+  __ movl(Address(EBX, count_offset), EDI);

[srdjan, 2014/07/10 17:07:36]

Are you certain this is better in ia32? The new code has 5 instructions (vs 2)
in most frequently used path?

[zra, 2014/07/10 17:15:39]

I've sent you a link.

+
   __ movl(EAX, Address(EBX, target_offset));
-  __ addl(Address(EBX, count_offset), Immediate(Smi::RawValue(1)));
-  __ j(NO_OVERFLOW, &call_target_function, Assembler::kNearJump);
-  __ movl(Address(EBX, count_offset),
-          Immediate(Smi::RawValue(Smi::kMaxValue)));
-
   __ Bind(&call_target_function);
   // EAX: Target function.
   __ movl(EBX, FieldAddress(EAX, Function::instructions_offset()));
   __ addl(EBX, Immediate(Instructions::HeaderSize() - kHeapObjectTag));
   __ jmp(EBX);
   __ int3();
 }
 
 
 // Use inline cache data array to invoke the target or continue in inline
@@ skipping 473 matching lines @@
   const Register temp = ECX;
   __ movl(left, Address(ESP, 2 * kWordSize));
   __ movl(right, Address(ESP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32