Re: How to eliminate redundant constant move instructions

On Nov 2, 6:35 am, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:
> George Neuner <gneun...@comcast.net> wrote:
>
> (big snip on optimization and register loads)
>


> That is what register renaming is for. Usually using more than
> the architecturally specified number of registers, the CPU
> internally remaps the registers such that it can keep one value
> in a register while an instruction is being executed out of order.
>
> This is especially important for IA32, with so few registers,
> and for S/360 and S/370 floating point, again with few registers.


Well, for my original case, I mean optimize the codes


  rx <- 0
  ...
  use rx
  ...
  ry <- 0 <----which is redundant and can be removed
  use ry


into


  rx <- 0
  ...
  use rx
  ...
  use rx <-----------------


In this case, the 2nd 'use rx' instruction introduces true dependency
on "rx <- 0",
So register renaming won't help here, right?


Thanks

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