Billy Holmes wrote:
Richard Fish wrote:
FYI, -mcpu is deprecated, and a synonym for -mtune, which is implied
by -march. So you can just take it out and get the same effect.
I think some ebuilds filter out march, but don't filter out
mcpu/mtune, so you can still get some processor specific optimizations
out of it.
A quick grep of /usr/portage shows that many builds will use
replace-flags to replace one -march setting with another or with
-mtune/-mcpu.
There are a few that can filter -march altogether:
1. net-firewall/ipsec-tools: filters all "-march=c3"
2. media-libs/libvorbis: filters "-march=pentium?".
3. dev-lang/squeak: filters all -march, -mtune, -mcpu, and many many
other flags.
4. dev-libs/libffi: filters -march=k8, -march=athlon64, and march=opteron.
5. app-editors/emacs: filters all -march (only in 21.4-r1)
6. app-pda/iripdb: filters march=k8, -march=athlon64, and -march=opteron
7. media-tv/mythtv: filters all -march, -mtune, and -mcpu.
So for #1, 2, 4, 5, and 6, you are correct that mtune/mcpu could have
some benefit. However, IMO these are actually bugs...the ebuild should
be using replace-flags to set the appropriate -mtune option if it cannot
support -march.
For #3 & 7, you get no benefit of any march/mtune/mcpu settings.
Cheers,
-Richard
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