[PATCH] D93838: [LLVM] [SCCP] : Add Function Specialization pass

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer added a comment.

In D93838#2694031 <https://reviews.llvm.org/D93838#2694031>, @fhahn wrote:

> It should run at the same place in both LegacyPM and NewPM.  The fact that LTO is slow already is not a strong argument to make it substantially slower again :) In the end, it is always a trade-off between the benefits and the extra compile-time. I think one of the main concerns with the numbers you shared is that there appears to be couple of substantial increases in compile-time without any noticeable benefits. This is only a small sample of course and we probably need more data.

Agreed and I'm now looking into the pass manager business, that needs to be consistent, I can't imagine that the current inconsistency is by design. 
About numbers and goals, I shared initial findings in:

https://lists.llvm.org/pipermail/llvm-dev/2021-March/149380.html

My goals is that eventually this reaches parity with GCC: it gets enabled by default, and doesn't exceed compile-times in the ranges of +1.5% as that is what I have seen so far from GCC.

I am now deep diving in the algorithm to see where time could be spent and what and where we can improve things.


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