[ia32] Add cmpxchg8b instruction

Bug: v8:6532
Change-Id: I0871aaafff2385758449ddde923178d1c9e1ff8a
Reviewed-on: https://chromium-review.googlesource.com/1146998Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54620}

src/ia32/assembler-ia32.cc

@@ -785,6 +785,13 @@ void Assembler::cmpxchg_w(Operand dst, Register src) {
   emit_operand(src, dst);
 }
 
+void Assembler::cmpxchg8b(Operand dst) {
+  EnsureSpace enure_space(this);
+  EMIT(0x0F);
+  EMIT(0xC7);
+  emit_operand(ecx, dst);
+}
+
 void Assembler::lfence() {
   EnsureSpace ensure_space(this);
   EMIT(0x0F);

src/ia32/assembler-ia32.h

@@ -667,6 +667,7 @@ class Assembler : public AssemblerBase {
   void cmpxchg(Operand dst, Register src);
   void cmpxchg_b(Operand dst, Register src);
   void cmpxchg_w(Operand dst, Register src);
+  void cmpxchg8b(Operand dst);
 
   // Memory Fence
   void lfence();

src/ia32/disasm-ia32.cc

@@ -1500,6 +1500,8 @@ static const char* F0Mnem(byte f0byte) {
       return "bsf";
     case 0xBD:
       return "bsr";
+    case 0xC7:
+      return "cmpxchg8b";
     default:
       return nullptr;
   }
@@ -1801,6 +1803,13 @@ int DisassemblerIA32::InstructionDecode(v8::internal::Vector<char> out_buffer,
             get_modrm(*data, &mod, &regop, &rm);
             AppendToBuffer("%s %s,", f0mnem, NameOfCPURegister(regop));
             data += PrintRightOperand(data);
+          } else if (f0byte == 0xC7) {
+            // cmpxchg8b
+            data += 2;
+            AppendToBuffer("%s ", f0mnem);
+            int mod, regop, rm;
+            get_modrm(*data, &mod, &regop, &rm);
+            data += PrintRightOperand(data);
           } else if (f0byte == 0xAE && (data[2] & 0xF8) == 0xE8) {
             AppendToBuffer("lfence");
             data += 3;

test/cctest/test-disasm-ia32.cc

@@ -871,6 +871,8 @@ TEST(DisasmIa320) {
     __ cmpxchg_b(Operand(esp, 12), eax);
     __ cmpxchg_w(Operand(ebx, ecx, times_4, 10000), eax);
     __ cmpxchg(Operand(ebx, ecx, times_4, 10000), eax);
+    __ cmpxchg(Operand(ebx, ecx, times_4, 10000), eax);
+    __ cmpxchg8b(Operand(ebx, ecx, times_8, 10000));
   }
 
   // lock prefix.