[LLVMdev] Landing my new development on the trunk ...

[Brian West]

Eli Friedman <eli.friedman <at> gmail.com> writes:
> > Empirically the OSR optimization is compile-time faster than LSR. I have
> > also noticed that OSR has more "analysis" requirements: Induction Variable
> > User, Natural Loop Information, Canonicalize natural loops, and Scalar
> > Evolution Analysis. Both OSR and LSR require the Dominator Tree Construction
> > analysis pass.
> 
> My primary concern here is that if this code gets committed without
> anyone interested in actually using it, it will just end up orphaned,
> so there's no point to contributing it.

This work is part of the PACE project (http://pace.rice.edu/).  My team has
funding for another three years and is committed to maintaining this code.


> > I did not mention in the original email (and should have) that OSR needs
> > -instcombine to be run after it for cleanup. Also -licm, -reassociate, -gvn
> > and -sccp can be enabling optimizations for OSR.
> 
> Hmm... perhaps that could be partially fixed using the InstSimplify
> infrastructure.

OSR can produce induction variables that are not used.  -instcombine finds the
unused induction variables and deletes them (which is super cool btw :)).  I am
unsure if InstructionSimplify can fix that.


> 
> -Eli
> 

thanks,
Brian