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

At 01:05 21.01.00 , Gabriel Paubert wrote:

On Thu, 20 Jan 2000, Franz Sirl wrote:

quoted

It depends a little bit on the usage of the asm's if the memory (either
global or local) clobber is needed or not. If you use them for

read/writes to HW

quoted

registers needing ordering (which is very likely here since we talk about
graphics HW), the compiler can only decide on the memory usage defined

by the

quoted

clobbers/memory inputs on how to order the inlines (volatile has no

effect on

quoted

this).

Do you mean that a volatile memory reference can be reordered wit an asm
volatile statement ? I thought theat this was not possible.

quoted

From GCC's documentation:

   "You can prevent an `asm' instruction from being deleted, moved
significantly, or combined, by writing the keyword `volatile' after the
`asm'."

You might disagree, but I consider that moving across a volatile memory
reference is a _significant_ move, a very significant one.

asm volatile doesn't declare any volatile memory references! What makes you
think it does?
There was a lengthy discussion about this with Richard Henderson on the
gcc/egcs lists a while ago. The result was a rewrite of
linux/include/asm-ppc/io.h in the kernel to it's current state.

Franz.


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