[gentoo-dev] Re: Moving CPU flags into USE_EXPAND

[Martin Vaeth]

Christopher Head <chead@×××××.ca> wrote:
>
> All that requires is knowing the names, though; it would be
> fine if no package actually uses the feature yet.

++

More precisely: When changing the names anyway,
IMHO it would be a very good idea to follow the convention of the
"flag" names in /proc/cpuinfo and add all flags supported
there as possible USE-flags, no matter, whether they are currently
used in some package or not.
The list might still be extended when a new processor with new features
comes out.

If this is done properly, the user could easily write a script to set
these flags appropriate for his current machine. One might even give
portage a "--use-native" switch (or FEATURE=use-native)
which sets the USE defaults corresponding to the current
/proc/cpuinfo output. The latter is what typical desktop users
probably would prefer: A complete analogue of CFLAGS=-march=native;
just generating optimal code for his machine, without requiring
the user to understand all the fancy details of his processor.

To properly support packages which can choose the appropriate code
at runtime, I suggest to add in addition an "all" flag which just
compiles in all possible optimized code-paths.