[PATCH] D11915: Let edge weight be always greater than zero in both BPI and MBPI.

[Xinliang David Li via llvm-commits]

I suggest merge it with your previous normalization patch.

David


On Tue, Aug 11, 2015 at 3:48 PM, Cong Hou <congh at google.com> wrote:
>
>
> thanks,
> Cong
>
> On Tue, Aug 11, 2015 at 3:26 PM, Xinliang David Li <davidxl at google.com>
> wrote:
>>
>> On Tue, Aug 11, 2015 at 3:07 PM, Cong Hou <congh at google.com> wrote:
>> > congh added a comment.
>> >
>> > In http://reviews.llvm.org/D11915#222110, @davidxl wrote:
>> >
>> >> Ok -- it is a very messy situation that need lots of cleanup
>> >> (summarized below).  For now, since the only producer of zero weight for BPI
>> >> is from 'opt' by reading developer's hand writing .ll file, I suggest simply
>> >> set zero weight to 1 in calcMetaDataWeights to match
>> >> BlockFrequencyInfoImpl's behavior.
>> >
>> >
>> > Assume the user uses weights 0 and 1 to represent that one edge is very
>> > very cold and another one is very very hot, then this modification makes
>> > them to 1 and 1, which has the totally different meaning.
>>
>> True -- and that will be fixed in the future. The question is does
>> this regress from the current behavior? If not, take the simpler fix
>> for now.
>
>
> OK. So in this patch we can just turn zero weights into 1 in BPI, right? I
> will update the patch accordingly.
>
> Cong
>
>>
>>
>> David
>>
>>
>> >
>> >>
>> >
>> >>
>> >
>> >>  -------------------
>> >
>> >>
>> >
>> >> Current situation:
>> >
>> >>
>> >
>> >> 1. there is no client (other than opt) producing zero weight for BPI
>> >
>> >> 2. BPI can have missing weights (empty map entry) -- in which case, the
>> >> edge weight returned is DEFAULT_WEIGHT= 16 for MBPI
>> >
>> >
>> > I think you mean MBB&MBPI as 3) & 6) below are for MBB.
>> >
>> >> 3. the default weight in the setter interface is '0' -- which can not
>> >> be differentiated with real zero weight
>> >
>> >> 4. when Weight list for a BB is empty, the getter interface returns 16
>> >> as the default weight.
>> >
>> >
>> > Here MBB returns 0 but MBPI turns it into 16.
>> >
>> >> 5. the getter interface also unconditionally change 0 weight into
>> >> DEFAULT_WEIGHT == 16
>> >
>> >> 6. the weight list and successor list can be out of sync.
>> >
>> >
>> >
>> > http://reviews.llvm.org/D11915
>> >
>> >
>> >
>
>