Recommended CFLAG for Pentium4 (IBM T30)

[Ijo]

I'm about to receive a T30 which has a Pentium4. I want to build from stage1, but I've seen lots of msgs around about the problem of using -march=pentium4.

Is there still a problem with 1.4RC4?
What's your CFLAG suggestion for a Pentium4 for a well optiomized system (not necesary a maximum optimization)?
Whould it make a real noticeable difference to compile with -march=pentium3?

thanks in advance,
ijo

[Megaptera]

-march=pentium4 is problematic with gcc 3.2.2 -- it makes buggy code in some situations. Unless you don't mind using a masked version of gcc (3.2.3 or 3.3) then stick with -march=pentium3, but the problem is fixed in more recent releases.

I keep my cflags pretty conservative, personally, but I do use 3.2.3 with "-march=pentium4 -O3 -pipe -fomit-frame-pointer". There are some ebuilds out there, like XFree86 4.3.0, that will automatically change march=p4 to march=p3, though. As for noticeable, well, I guess that depends on how close attention you're paying -- I haven't seen any benchmarks :)

My reasoning is like this: GCC 3.2.3 seems to be within my own tolerance for stability, and even though I wouldn't be able to tell you which ebuilds switch p4 for p3 just by using the program, it's not like anything's going to suffer by using p4. I've personally had no problems with it.

Oh, and side-note: Stuff like this isn't a problem with 1.4rc4 or anything like that. The Gentoo version number more accurately represents how far the install CD has progressed than the Gentoo system that will be installed; I have a fairly anemic test box that was originally installed off of a 1.1 cd, and I could theoretically get it to use -march=pentium4* with no problems just by using the right gcc.


*it's not actually a p4, so -march=p4 wouldn't technically work but for an entirely different and obvious reason :) But if it were, it would work fine.
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