[LLVMdev] fix for loop scale limiting in BFI

Diego Novillo dnovillo at google.com
Fri Mar 27 13:12:01 PDT 2015

On Fri, Mar 27, 2015 at 4:09 PM, Xinliang David Li <xinliangli at gmail.com> wrote:
> How about only removing the scaling limit when PGO is on? I don't see the
> need for this change without PGO.

This is what my patch does, and it's getting into issues.  With the
scaling limit gone, the frequencies propagated overflow 64bits, so
they need to be scaled down to a 64bit space.

To be on the safe side, my patch is mapping them down to a 32bit
space, but I am squishing them too much on  the lower end. So regions
of the CFG that before had distinct temperatures are now showing up
with frequency == 1.

I need a better smoother for the mapping from the Scale64 floats down
to 64bit (or 32bit) integers.


More information about the llvm-dev mailing list