[PATCH] D69027: [llvm-dwarfdump][Statistics] Fix calculation of OffsetToFirstDefinition

[Kristina Bessonova via Phabricator via llvm-commits]

krisb added a comment.

@dblaikie thanks, David! This is definitely needed to be kept in mind.

In D69027#1728577 <https://reviews.llvm.org/D69027#1728577>, @avl wrote:

> > I see the primary value of this statistic to allow us to see change — then a human has to make judgement what that change means.
>
> That is exactly the reason why I propose to drop calculation of OffsetToFirstDefinition. For the already discussed example, currently visible change would be 100%->100% For the case without OffsetToFirstDefinition there would be something like 20%->30% which makes change visible.


Regarding tracking changes and their visibility, dropping calculation of OffsetToFirstDefinition is not a panacea, especially if we talking about 'coverage buckets'. In cases when we have a large enclosing scope and a relatively small variable's scope (or coverage), we will see no changes because they will be less than 10% to exceed the bucket's threshold. 
So, the only statistic we can rely on is the absolute number of bytes covered by variable's DW_AT_locations. And maybe on the number of bytes covered divided by the number of bytes in an enclosing scope. Doesn't this make even significant changes not noticeable?


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