On Mar 6, 2008, at 2:06 PM, Andi Kleen wrote:
On Thu, Mar 06, 2008 at 12:56:16PM -0800, H. Peter Anvin wrote:
Richard Guenther wrote:
A patched GCC IMHO makes only sense if it is always-on, yet
another option
won't help in corner cases. And corner cases is exactly what
people seem
to care about. For this reason that we have this single release,
4.3.0,
that
behaves "bad" is already a problem.
The option will help embedded vendors who can guarantee that it's
not a
problem.
For very very low values of "help".
To be realistic it is very unlikely anybody will measure a difference
from a few more or a few less clds in a program. It's not that they're
expensive instructions
They aren't? According to http://www.agner.org/optimize/instruction_tables.pdf
, they have a latency of 52 cycles on at least one popular x86 chip.
-Chris
