[PATCH] D147740: [NFC][llvm-profdata] Refactoring Sample Profile Reader to increase FDO build speed

[Wenlei He via Phabricator via llvm-commits]

wenlei added a comment.

In D147740#4250599 <https://reviews.llvm.org/D147740#4250599>, @davidxl wrote:

> In D147740#4250545 <https://reviews.llvm.org/D147740#4250545>, @aeubanks wrote:
>
>> as somebody with very little context for this, is it possible to use faster hashing algorithms?
>
> faster hashing may help, but I think the intention of the patch is to eliminate unnecessary computation completely.

Might be a bit off topic, but we have seen MD5 hashing in the top hottest functions in profile of llvm itself when compiling workloads with compact binary profile in the past.

It'd be great if we can transition to cheaper hash (e.g. xxhash) for all profile format. We need hash with all distribution, but we don't need cryptographic hash.

I think it's doable to switch profile format to use xxhash, with a flag in header to tell reader what hash to expect. But agreed that it's orthogonal to this patch.


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