[LLVMdev] RFC - Improvements to PGO profile support

[Diego Novillo]

On Tue, Mar 24, 2015 at 1:48 PM, Bob Wilson <bob.wilson at apple.com> wrote:
>
>> On Mar 24, 2015, at 10:27 AM, Xinliang David Li <davidxl at google.com> wrote:
>>
>>   2.3) remove the 'laplace rule of succession' which can be very harmful
>
> I have not seen any consensus on this. I’m not at all convinced this would be a good idea. From what I’ve seen, using LaPlace’s rule avoids really bad behavior in cases where the counts are very small and has almost no impact when the counts are large.

Duncan and I chatted briefly about this on IRC. I'm going to
experiment with only applying laplace smoothing if any scaled weights
are 0. AFAIU, usage of this rule is really just trying to avoid having
downstream users deal with 0 weights. Duncan, please whack me with a
clue stick if I totally misrepresented our conclusions.


Diego.