Re: Maximum Register Pressure?

Sid Touati <Sid-pasdespam.Touati-nospam@inria-nospam.fr>
14 Mar 2006 00:50:18 -0500

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Related articles
Maximum Register Pressure? ammalik@cs.uwaterloo.ca (2006-03-12)
Re: Maximum Register Pressure? Sid-pasdespam.Touati-nospam@inria-nospam.fr (Sid Touati) (2006-03-14)
Re: Maximum Register Pressure? Sid.Touati@inria-nospam.fr (Sid Touati) (2006-03-14)
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From: Sid Touati <Sid-pasdespam.Touati-nospam@inria-nospam.fr>
Newsgroups: comp.compilers
Date: 14 Mar 2006 00:50:18 -0500
Organization: I.N.R.I.A Rocquencourt
References: 06-03-039
Keywords: registers

ammalik@cs.uwaterloo.ca a écrit :
> I have a question. Does an optimal schedule of a basic block also
> gives maximum register pressure for that basic block?
>
> Regards
> Abid


No;


here is a DAG represented with data dependences :
a -> b : flow arc latency = 20
c -> d : flow arc latency = 1
e -> f : flow arc latency = 1


A time-optimal schedule is of latency 20 (assuming enough resources).
Assuming no exit values, ie. the operations b d f do not write into
registers, you can use only two registers in a time-optimal schedule
(schedule the whains a->d and e-> in serial), while the maximal register
pressure is 3 registers (a c e simultaneously alive)




S



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