Re: Maximum Register Pressure?

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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