[arm][arm64] Improve CountTrailingZero implementation.

src/arm/assembler-arm.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 932 matching lines @@
              Condition cond = al);
 
   void uxtb(Register dst, Register src, int rotate = 0, Condition cond = al);
   void uxtab(Register dst, Register src1, Register src2, int rotate = 0,
              Condition cond = al);
   void uxtb16(Register dst, Register src, int rotate = 0, Condition cond = al);
   void uxth(Register dst, Register src, int rotate = 0, Condition cond = al);
   void uxtah(Register dst, Register src1, Register src2, int rotate = 0,
              Condition cond = al);
 
+  // Reverse the bits in a register.
+  void rbit(Register dst, Register src, Condition cond = al);
+
   // Status register access instructions
 
   void mrs(Register dst, SRegister s, Condition cond = al);
   void msr(SRegisterFieldMask fields, const Operand& src, Condition cond = al);
 
   // Load/Store instructions
   void ldr(Register dst, const MemOperand& src, Condition cond = al);
   void str(Register src, const MemOperand& dst, Condition cond = al);
   void ldrb(Register dst, const MemOperand& src, Condition cond = al);
   void strb(Register src, const MemOperand& dst, Condition cond = al);
@@ skipping 676 matching lines @@
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARM_ASSEMBLER_ARM_H_