On 13/12/2016 02:36, Mingye Wang (Arthur2e5) wrote:
> GCC 6's __attribute__((target_clones)) feature looks quite exciting to
> me, but I cannot understand why it is designed to take, say, a single
> string option like "sse2,avx2" and make it two separate
> __attribute__((target)) clones. Using commas in single option strings
> sounds like defeating the whole purpose of allowing multiple options;
> furthermore, after some inspection on the source, it seems that all the
> options will be smashed together with a comma and processed as a single
> string.
>
> So take __attribute__((target_clones("sse3,tune=generic,default",
> "arch=ivybridge"))) as an example. Instead of creating two clones with
> targets "sse3,tune=generic,default" and "arch=ivybridge" respectively,
> GCC's target_clones would create three clones with their targets defined
> as "sse3" "default", "tune=generic", and "arch=ivybridge". This
> behavior, although documented somehow, is confusing.
>
> Could anyone please tell me why GCC decided to go with such "smash the
> string options together and split later" design? Is it possible to have
> GCC change this behavior in later releases, if it is indeed a design flaw?
Hello,
Out of curiosity, I took a peak at the source code.
(1.6 GiB repo, clone requires 15 minutes on fast connection)
$ git clone git://gcc.gnu.org/git/gcc.git
AFAICT (?) the implementation is in gcc/multiple_target.c
Likely candidates are ab50af2a61a65 (initial) and
cb6c05f855c41 (update).
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=229595
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=242608
I've CCed the respective authors.
Regards.
