3 ms·

>Not having condition codes and PC not being a GPR are major advantages here. What's GPR?

• hakfoo 2y ago
  General Purpose Register?
  • brokenmachine 2y ago
    Why is that an advantage?
    • brucehoult 2y ago
      Because instructions that change the PC have to be handled specially because if not correctly predicted taken/not taken, and the target address) then they cause a pipeline break, throwing away speculatively executed work etc. When the PC is a GPR then any instruction (with PC as the destination) can be a jump to different code. Even a subtract, for example. In fact I have many times written `sub pc,pc,#3` to switch an Arm CPU to running the next instruction in Thumb mode. Gross.
      • brokenmachine 2y ago
        Cool, makes sense. Thanks for the explanation.
    • snvzz 2y ago
      Because PC as GPR complicates implementations immensely, for virtually no benefit.