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Re: Problems with the way we calculate costs


On Mon, 11 Sep 2000, Geoff Keating wrote:

> It'd probably be better if it worked like the original code; that is,
> the cost of a non-fixed hard register is 2, compared to 1 for a
> pseudo.  This ensures a pseudo gets preference, which would be the
> usual case because such hard registers should be copied into pseudos
> immediately after they appear.

The original code mixed up these register pressure considerations with
the calculation of the cost of an operation.  I still think this is a
bad idea.  It also won't reliably prevent lifetimes of hard registers
from being lenghtened (think of computing the cost of a shift of a
hardreg as opposed to multiplication of a pseudo).


Bernd


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