Removes branches from LoadTaggedClassIdMayBeSmi.

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 255 matching lines @@
 }
 
 
 void Assembler::leal(Register dst, const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x8D);
   EmitOperand(dst, src);
 }
 
 
+void Assembler::cmove(Register dst, Register src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x0F);
+  EmitUint8(0x44);
+  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 2365 matching lines @@
 
 
 void Assembler::CompareClassId(Register object,
                                intptr_t class_id,
                                Register scratch) {
   LoadClassId(scratch, object);
   cmpl(scratch, Immediate(class_id));
 }
 
 
-void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  testl(object, Immediate(kSmiTagMask));
-  Label not_smi, done;
-  j(NOT_ZERO, &not_smi, Assembler::kNearJump);
-  movl(result, Immediate(Smi::RawValue(kSmiCid)));
-  jmp(&done, Assembler::kNearJump);
-  Bind(&not_smi);
-  LoadClassId(result, object);
+void Assembler::LoadTaggedClassIdMayBeSmi(
+    Register result, Register object, Register tmp) {
+  ASSERT(object != tmp);
+  ASSERT(result != tmp);
+
+  // 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.
+  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.
   SmiTag(result);
-  Bind(&done);
 }
 
 
 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