Implemented the Word64Popcnt TurboFan operator for x64.

src/x64/disasm-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <assert.h>
 #include <stdarg.h>
 #include <stdio.h>
 
 #if V8_TARGET_ARCH_X64
 
@@ skipping 1834 matching lines @@
     // SHLD, SHRD (double-precision shift), BTS (bit set).
     AppendToBuffer("%s ", mnemonic);
     int mod, regop, rm;
     get_modrm(*current, &mod, &regop, &rm);
     current += PrintRightOperand(current);
     if (opcode == 0xAB) {
       AppendToBuffer(",%s", NameOfCPURegister(regop));
     } else {
       AppendToBuffer(",%s,cl", NameOfCPURegister(regop));
     }
-  } else if (opcode == 0xBC) {
+  } 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);
-    AppendToBuffer("%s,", NameOfCPURegister(regop));
-    current += PrintRightOperand(current);
-  } else if (opcode == 0xBD) {
-    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 == 0x0B) {
     AppendToBuffer("ud2");
   } else {
     UnimplementedInstruction();
   }
   return static_cast<int>(current - data);
 }
 
@@ skipping 610 matching lines @@
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_X64