Re: How to eliminate redundant constant move instructions

From	amker <can.finner@gmail.com>
Newsgroups	comp.compilers
Subject	Re: How to eliminate redundant constant move instructions
Date	2011-11-01 19:35 -0700
Organization	Compilers Central
Message-ID	<11-11-008@comp.compilers> (permalink)
References	<11-10-019@comp.compilers> <11-11-004@comp.compilers> <11-11-005@comp.compilers>

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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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Thread

How to eliminate redundant constant move instructions "Amker.Cheng" <amker.cheng@gmail.com> - 2011-10-31 17:53 +0800
  Re: How to eliminate redundant constant move instructions Kaz Kylheku <kaz@kylheku.com> - 2011-10-31 17:08 +0000
    Re: How to eliminate redundant constant move instructions amker <can.finner@gmail.com> - 2011-11-01 19:01 -0700
    Re: How to eliminate redundant constant move instructions mac <acolvin@efunct.com> - 2011-11-03 02:20 +0000
  Re: How to eliminate redundant constant move instructions George Neuner <gneuner2@comcast.net> - 2011-11-01 14:32 -0400
    Re: How to eliminate redundant constant move instructions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-11-01 22:35 +0000
      Re: How to eliminate redundant constant move instructions amker <can.finner@gmail.com> - 2011-11-01 19:35 -0700
      Re: How to eliminate redundant constant move instructions amker <amker.cheng@gmail.com> - 2011-11-01 21:04 -0700
      Re: How to eliminate redundant constant move instructions George Neuner <gneuner2@comcast.net> - 2011-11-02 12:38 -0400
        Re: How to eliminate redundant constant move instructions Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 03:20 +0000
          Re: How to eliminate redundant constant move instructions George Neuner <gneuner2@comcast.net> - 2011-11-04 13:27 -0400
            Re: How to eliminate redundant constant move instructions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-11-04 21:19 +0000
        Re: How to eliminate redundant constant move instructions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-11-03 03:32 +0000
    Re: How to eliminate redundant constant move instructions amker <can.finner@gmail.com> - 2011-11-01 19:21 -0700
      Re: How to eliminate redundant constant move instructions George Neuner <gneuner2@comcast.net> - 2011-11-04 17:26 -0400
        Re: How to eliminate redundant constant move instructions amker <amker.cheng@gmail.com> - 2011-11-07 17:33 -0800
          Re: How to eliminate redundant constant move instructions Wei-Jen Chen <chenwj@cs.NCTU.edu.tw> - 2011-11-10 08:04 +0000
          Re: How to eliminate redundant constant move instructions George Neuner <gneuner2@comcast.net> - 2011-11-10 18:18 -0500
    Re: How to eliminate redundant constant move instructions amker <amker.cheng@gmail.com> - 2011-11-01 20:58 -0700

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