Re: How to eliminate redundant constant move instructions

Kaz Kylheku <kaz@kylheku.com>
Thu, 3 Nov 2011 03:20:32 +0000 (UTC)

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Related articles
[5 earlier articles]
Re: How to eliminate redundant constant move instructions can.finner@gmail.com (amker) (2011-11-01)
Re: How to eliminate redundant constant move instructions can.finner@gmail.com (amker) (2011-11-01)
Re: How to eliminate redundant constant move instructions amker.cheng@gmail.com (amker) (2011-11-01)
Re: How to eliminate redundant constant move instructions amker.cheng@gmail.com (amker) (2011-11-01)
Re: How to eliminate redundant constant move instructions gneuner2@comcast.net (George Neuner) (2011-11-02)
Re: How to eliminate redundant constant move instructions acolvin@efunct.com (mac) (2011-11-03)
Re: How to eliminate redundant constant move instructions kaz@kylheku.com (Kaz Kylheku) (2011-11-03)
Re: How to eliminate redundant constant move instructions gah@ugcs.caltech.edu (glen herrmannsfeldt) (2011-11-03)
Re: How to eliminate redundant constant move instructions gneuner2@comcast.net (George Neuner) (2011-11-04)
Re: How to eliminate redundant constant move instructions gah@ugcs.caltech.edu (glen herrmannsfeldt) (2011-11-04)
Re: How to eliminate redundant constant move instructions gneuner2@comcast.net (George Neuner) (2011-11-04)
Re: How to eliminate redundant constant move instructions amker.cheng@gmail.com (amker) (2011-11-07)
Re: How to eliminate redundant constant move instructions chenwj@cs.NCTU.edu.tw (Wei-Jen Chen) (2011-11-10)
[1 later articles]
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From: Kaz Kylheku <kaz@kylheku.com>
Newsgroups: comp.compilers
Date: Thu, 3 Nov 2011 03:20:32 +0000 (UTC)
Organization: A noiseless patient Spider
References: 11-10-019 11-11-004 11-11-005 11-11-014
Keywords: optimize

On 2011-11-02, George Neuner <gneuner2@comcast.net> wrote:
> Yes. But the compiler can't count on register renaming ... it can see
> only the architectural named registers. If the code in question had
> copied Rx-> Ry then renaming would have been possible, but instead the
> code performed a constant load to each register. No possibility of
> rename sharing there.


If the register holds a value that is used, but not clobbered, then renaming is
moot. The two blocks of code both depend on rx being zero, and so nothing is
achieved by splitting the instruction set register into two physical registers.



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