[LLVMdev] Effective Sign Extension Elimination

[Chris Lattner]

On Thu, 4 Jan 2007, Bill Wendling wrote:
> Now that we have sign/zero extensions, have people given thought to
> the elimination of these? There's a paper I downloaded a few years
> ago called "Effective Sign Extension Elimination" by M. Kawahito, H.
> Komatsu, and T. Nakatani.

Sign extension elimination is most useful in the backend, when targeting 
processors like PowerPC that have a single register width (e.g. 32-bits). 
We already do quite a bit of sign extension removal in the dag combiner, 
but this is limited to a single basic block at a time.  In the future, I'd 
like to extend the selectiondag to work on entire functions at a time, 
which would increase the scope of this optimization, but this isn't likely 
to happen in the near future.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/