16. Real Stuff : ARMv8(64-bit) Instructions

16.1. ARM v8 Instructions

• In moving to 64-bit

  → memory addressing 때문에 32bit → 64bit으로 바뀜

  → MIPS와 비슷해짐

• ARM v8 resembles MIPS

  • No conditional execution field
  • GPR set expanded to 32
  • Branch if equal/branch if not equal instructions

17. Real Stuff : x86 Instructions

17.1. The Intel x86 ISA

• Evolution with backward compatibility
  • 8086(1978) : 16-bit extension to 8080
    • Complex instruction set(CISC)
  • Pentium(1993) : superscalar, 64-bit datapath
    • Later versions added MMX(multi-Media eXtension) instructions
      • MMX : SIMD(Single Instruction Multiple Data) 명령어 집합
    • The infamous FDIV(Floating point division) bug
  • AMD64(2003) : extended architecture to 64bits
  • EM64T - Extended Memory 64 Technology(2004)
    • AMD64 adopted by Intel

17.1. x86 Instruction Encoding

• Variable length encoding
  • Postfix bytes specify addressing mode
  • Prefix bytes modify operation

18. Fallacies and Pitfalls

18.1. Fallacies

• Powerful instruction ⇒ higher performance ?
  • Fewer instructions required
  • But complex instructions are hard to implement
    • May slow down all instructions, including simple ones
• Use assembly code for high performance ?
  • But modern compilers are better at dealing with modern processors
• Backward compatibility → Instruction set doesn’t change ?
  • But they do accrete more instructions

18.2. Pitfalls

• Sequential words are not at sequential addresses
  • Increment by 4
• Keeping a pointer to an automatic variable after procedure returns
  • Pointer becomes invalid when stack popped

19. Concluding Remarks

19.1. Concluding Remarks