On Thu, Sep 03, 2015 at 10:09:36AM -0600, Jeff Law wrote: > >>You will end up with a *lot* of target hooks like this. It will also > >>make testing harder (less coverage). I am not sure that is a good idea. > > > >We certainly need a lot more target hooks in general so GCC can do the > >right thing > >(rather than using costs inconsistently all over the place). But that's a > >different > >discussion... > Let's be very careful here, target hooks aren't always the solution. > I'd rather see the costing models fixed and use those across the board. > But frankly, I don't know how to fix the costing models.
Combine doesn't currently use costs to decide how to simplify and canonicalise things. Simplifications are what is simpler RTL; combine's job is to make fewer RTL instructions (which is not the same thing as fewer machine instructions, or cheaper instructions). Changing what is canonical based on target hooks would be, uh, interesting. Segher
