Better sequences for class id loading on ia32.

runtime/vm/assembler_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/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 272 matching lines @@
 
 
 void Assembler::cmove(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x0F);
   EmitUint8(0x44);
   EmitRegisterOperand(dst, src);
 }
 
 
+void Assembler::cmovne(Register dst, Register src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x0F);
+  EmitUint8(0x45);
+  EmitRegisterOperand(dst, src);
+}
+
+
 void Assembler::cmovs(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x0F);
   EmitUint8(0x48);
   EmitRegisterOperand(dst, src);
 }
 
 
 void Assembler::cmovns(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
@@ skipping 2398 matching lines @@
                                Register scratch) {
   LoadClassId(scratch, object);
   cmpl(scratch, Immediate(class_id));
 }
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(
     Register result, Register object, Register tmp) {
   ASSERT(object != tmp);
   ASSERT(result != tmp);
+  static const intptr_t kSmiCidSource = kSmiCid << RawObject::kClassIdTagPos;
 
-  // Make a copy of object since result and object can be the same register.
-  movl(tmp, object);
-  // Load up a null object. We only need it so we can use LoadClassId on it in
-  // the case that object is a Smi.
-  movl(result, Immediate(reinterpret_cast<intptr_t>(Object::null())));
-  // Check if the object is a Smi.
+  if (result == object) {
+    movl(tmp, object);
+  } else {
+    tmp = object;
+  }
+
+  // Make a dummy "Object" whose cid is kSmiCid.
+  movl(result, Immediate(reinterpret_cast<int32_t>(&kSmiCidSource) + 1));
+
+  // Check if object (in tmp) is a Smi.
   testl(tmp, Immediate(kSmiTagMask));
-  // If the object *is* a Smi, load the null object into tmp. o/w leave alone.
-  cmove(tmp, result);
-  // Loads either the cid of the object if it isn't a Smi, or the cid of null
-  // if it is a Smi, which will be ignored.
-  LoadClassId(result, tmp);
 
-  movl(tmp, Immediate(kSmiCid));
-  // If object is a Smi, move the Smi cid into result. o/w leave alone.
-  cmove(result, tmp);
-  // Finally, tag the result.
+  // If the object is not a Smi, use the original object to load the cid.
+  // Otherwise, the dummy object is used, and the result is kSmiCid.
+  cmovne(result, tmp);
+  LoadClassId(result, result);
+
+  // Tag the result.
   SmiTag(result);
 }
 
 
 static const char* cpu_reg_names[kNumberOfCpuRegisters] = {
   "eax", "ecx", "edx", "ebx", "esp", "ebp", "esi", "edi"
 };
 
 
 const char* Assembler::RegisterName(Register reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfCpuRegisters));
   return cpu_reg_names[reg];
 }
 
 
 static const char* xmm_reg_names[kNumberOfXmmRegisters] = {
   "xmm0", "xmm1", "xmm2", "xmm3", "xmm4", "xmm5", "xmm6", "xmm7"
 };
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32