Which is the first CPU that Intel has added conditional move instructions to?

Question

I remember having read about it somewhere… Could anyone shed some light on this?

score 4 · Accepted Answer · answered Dec 13 '10 at 14:01

4

According to Wiki, Pentium Pro. They are suprizingly old, and I wonder why do you still need a switch for GCC to use them.

answered Dec 13 '10 at 14:01

ruslik

1

Thank you. Although Wikipedia is not Wiki. :-) – Ryan Li Dec 13 '10 at 14:07
I also read somewhere that `gcc` doesn't use cmov instructions by default, but my `gcc` does. – Ryan Li Dec 13 '10 at 14:13
5

Switch for GCC is needed because CMOV is quite limited in comparison to MOV. See what Linux kernel guys say: http://ondioline.org/mail/cmov-a-bad-idea-on-out-of-order-cpus – gertas Dec 13 '10 at 14:15
@gertas: yes you are right, I made a mistake. Sometimes I even need to add the optimization flag for it to use conditional moves. – Ryan Li Dec 13 '10 at 14:27
I don't know how bad `CMOV`s are but I see ICC emits conditional moves very often. One can check it on https://gcc.godbolt.org/ – phuclv Jun 30 '15 at 11:16
@gertas your link is dead. on mobile here, can't offer replacement. – z0rberg's May 27 '19 at 14:47

score 2 · Answer 2 · answered Dec 13 '10 at 14:03

2

CMOV was introduced with Pentium Pro (commonly called i686)

answered Dec 13 '10 at 14:03

gertas

2 Answers2