Removes branches from LoadTaggedClassIdMayBeSmi.

runtime/vm/assembler_x64.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_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 436 matching lines @@
 
 
 void Assembler::leaq(Register dst, const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandREX(dst, src, REX_W);
   EmitUint8(0x8D);
   EmitOperand(dst & 7, src);
 }
 
 
+void Assembler::cmoveq(Register dst, Register src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  Operand operand(src);
+  EmitOperandREX(dst, operand, REX_W);
+  EmitUint8(0x0F);
+  EmitUint8(0x44);
+  EmitOperand(dst & 7, operand);
+}
+
+
 void Assembler::cmovgeq(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   Operand operand(src);
   EmitOperandREX(dst, operand, REX_W);
   EmitUint8(0x0F);
   EmitUint8(0x4D);
   EmitOperand(dst & 7, operand);
 }
 
 
@@ skipping 2858 matching lines @@
 }
 
 
 void Assembler::CompareClassId(Register object, intptr_t class_id) {
   LoadClassId(TMP, object);
   cmpl(TMP, Immediate(class_id));
 }
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  Label load, done;
-  testq(object, Immediate(kSmiTagMask));
-  j(NOT_ZERO, &load, Assembler::kNearJump);
-  LoadImmediate(result, Immediate(Smi::RawValue(kSmiCid)), PP);
-  jmp(&done);
-  Bind(&load);
-  LoadClassId(result, object);
+  ASSERT(object != TMP);
+  ASSERT(result != TMP);
+
+  // Make a copy of object since result and object can be the same register.
+  movq(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.
+  LoadObject(result, Object::null_object(), PP);
+  // Check if the object is a Smi.
+  testq(TMP, Immediate(kSmiTagMask));
+  // If the object *is* a Smi, load the null object into tmp. o/w leave alone.
+  cmoveq(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);
+
+  movq(TMP, Immediate(kSmiCid));
+  // If object is a Smi, move the Smi cid into result. o/w leave alone.
+  cmoveq(result, TMP);
+  // Finally, tag the result.
   SmiTag(result);
-  Bind(&done);
 }
 
 
 static const char* cpu_reg_names[kNumberOfCpuRegisters] = {
   "rax", "rcx", "rdx", "rbx", "rsp", "rbp", "rsi", "rdi",
   "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
 };
 
 
 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",
   "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15"
 };
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64