Fwd: Re: still no accelerated X ($#!$*)

[Gabriel Paubert]

	Hi,

> In this particular case, the base address can change (but very very rarely
> such as writing to one Aperature or Another on the Rage 128 card) and all of
> the writes are made to either the card memory mapped io or the frame buffer
> itself.

Then the memory clobber would force the compiler to reload base_addr
between 2 writes to the frame buffer.

> Should I not include the : "memory" clobber in this case?  Will it hurt
> performance much?

I think that it is not necessary: the best thing with a compiler which
performs alias analysis might be to tell the truth

asm ("stwbrx %1,%2,%3"
     : "=m" (*(volatile unsigned *)(base_addr+regindex))
     : "r" (regdata), "b" (base_addr), "r" (regindex));

Note we don't use %0, and it won't produce any aditional code. You may
want to check what the compiler would have generated as addressing mode
by appending " # %0" at the end of the code string.

I truly wish there were a constraint for indexed addressing modes (anyway
this will be necessary for proper Altivec support).

	Gabriel.


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