Re: Intel vs AMD x86-64

Timothy Miller
2004-02-26T15:54:23Z

Nakajima, Jun wrote:
> Yes, that's the very reason I said "useless for compilers." The way
> IP/RIP is updated is different (and implementation specific) on those
> processors if 66H is used with a near branch. For example, RIP may be
> zero-extended to 64 bits (from IP), as you observed before.
>

This is obviously an extremely minor nit-pick, because we're talking
about one instruction here with an interpretation that is far from
obvious, but given that there are now only two architectures which
support x86-64, did Intel choose to do it differently from AMD because
it was poorly defined, or because it wasn't important enough to want to
impact the efficiency of the design?

There are people who would go way out of their way to get a 5%
improvement in performance or decrease in size. If using 66H with near
branches could in some way do that, they would really really want to use
it. This is why I'm curious.