Implemented the Word64Popcnt TurboFan operator for x64.

src/x64/disasm-x64.cc

Index: src/x64/disasm-x64.cc
diff --git a/src/x64/disasm-x64.cc b/src/x64/disasm-x64.cc
index 94a5ee713ebc40923688ea20e254999b3a1e70a6..cad4a461c3b409937e745fc24b7cb35df0a63102 100644
--- a/src/x64/disasm-x64.cc
+++ b/src/x64/disasm-x64.cc
@@ -1852,13 +1852,8 @@ int DisassemblerX64::TwoByteOpcodeInstruction(byte* data) {
     } else {
       AppendToBuffer(",%s,cl", NameOfCPURegister(regop));
     }
-  } else if (opcode == 0xBC) {
-    AppendToBuffer("%s%c ", mnemonic, operand_size_code());
-    int mod, regop, rm;
-    get_modrm(*current, &mod, &regop, &rm);
-    AppendToBuffer("%s,", NameOfCPURegister(regop));
-    current += PrintRightOperand(current);
-  } else if (opcode == 0xBD) {
+  } else if (opcode == 0xB8 || opcode == 0xBC || opcode == 0xBD) {
+    // POPCNT, CTZ, CLZ.
     AppendToBuffer("%s%c ", mnemonic, operand_size_code());
     int mod, regop, rm;
     get_modrm(*current, &mod, &regop, &rm);