[PATCH] D158689: [llvm-profdata] Use llvm::DenseMap in SampleProfileMap

[David Li via Phabricator via llvm-commits]

davidxl added a comment.

In D158689#4631824 <https://reviews.llvm.org/D158689#4631824>, @wenlei wrote:

>> This brings up to 8% speed up (31.4s vs 29.0s) when reading a large test profile, and 5% speedup (0.82s vs 0.78s) when reading the function offset table alone.
>
> @huangjd what were you measuring exactly? is that the total wall clock / cycles for SampleProfileLoader for all modules, or were you just measuring SampleProfileReader time? From the line above, it sounds like you were measuring the latter. However, the impact of changing a container is not limited the creation of that container.
>
> So measuring SampleProfileLoader would give us a more accurate picture of overall impact, including container construction (which is SampleProfileReader), updating and consumption (which are other parts of SampleProfileLoader).
>
> OTOH, if the impact on SampleProfileLoader is significant, we should be able to see a difference in e2e compilation. I agree that in the end e2e compilation is what matters.

true.

However, when picking the compilations to examine, the slowest ones may not be the good candidate -- as they are likely triggering pathological compile time issue elsewhere thus makes  profile loading less significant.

William's experiment may also have FSAFDO on, thus have more rounds of loading.


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