Hi there. I'm a long mailing-list lurker, and I use GCC quite a bit for
embedded software development.
Most of the stuff I write is performance critical, and I always find
myself in the same situation: I spend counter less hours to unswitch
loops by hand because the built-in loop unswitcher is not always smart
when multiple variables can be unswitched. Also you can not
enable/disable loop unswitching on a per-function basis.
I like to structure my source by function (so you find related stuff in
the same source). Therefore I always have uncritical control-code and
critical inner loop functions in the same translation unit. This is bad
because I can't simply enable the optimization without sacrificing
code-space (and as such performance due to instruction cache misses).
Some kind of pragma/attribute to hint the compiler into making a better
decision and enabling/disabling unswitching for entire functions would
be great help for my work. I have no real idea how such a pragma should
look like because I'm not familiar with the gcc internals.
I hope it's ok to place requests like this onto the mailinglist.
Cheers, and keep up the good work,
Nils
