[geeks] Itanium 32 bit performace.... hahahaha

[Francisco Javier Mesa-Martinez]

On Thu, 11 Dec 2003, Charles Shannon Hendrix wrote:
> Did the DEC compiler around 1996 pack bytes to make it more efficient?

Hum, that is a good question. I don't know how efficient is to pack bytes
into a word, since you may still need to do a few shifts on that word to
get the bits that you are interested in.

> Anyone know how GNU C handles it?

GNU C used to be pretty bad at it, but I have not look at the internals
for a while, I need to check on it. I know the first quick hack did use up
a whole word even for a single byte, so it chew memory like no body's
business but that was in the 2.6/7 days.

> I remember it eating RAM quickly on some projects, and not others.
> Maybe it was inconsistent.
>
> There were problems with using a lot of barrier instructions on the
> 21064 as well.

The 21064 was geared towards making the common case fast, barrier
instructions may have been deemed to not be that common.

> The later Alphas are so good at preduction, it almost doesn't matter.

I do not follow here, they do have prediction and some serious rebuffering
capabilities, so I assume that you wanted to say that the 21164 and later
are less dependant on good code ordering, which is true (when compared
with the 21064).