[PATCH] D96035: [dsymutil][DWARFlinker] implement separate multi-thread processing for compile units.

Fri May 6 11:30:58 PDT 2022

avl added a comment.

> I'm (still) very excited about this. I'm really happy that this lives behind a flag which addresses most of my original concerns. Making this the default in dsymutil would require a bunch of qualification but this approach allows me to do that gradually. One thing I suggested earlier I think was to run the lldb test suite with the new flag and see if that breaks anything. Did you ever get around to that?

yes, I did. This is the set of tests passed by this patch:

It passed llvm/test/tools/dsymutil lit tests.
It passed check-llvm, check-clang, **check-lldb**.
It passed llvm-dwarfdump --verify for all llvm&clang binaries.
It passed llvm-dwarfdump --types-compat-dump for all llvm&clang binaries.

> Jim expressed some concerns about trying to squeeze everything in the same compilation unit. Greg, do you share that concern? Do we expect this will negatively impact lldb's performance? It would probably be worthwhile to do a few performance experiments here as well to make sure this doesn't regress debugging performance.

I will check the performance results and post them here. Though I think the performance degradation would not be significant.

Anyway, I think it might be a good idea to split a single type unit into several units. The question is - by which criteria? @clayborg suggested dividing it by declaration file basis. So that a separate unit would be created for every declaration file. I think that solution creates significant fragmentation. That fragmentation would lead to increased resulting DWARF size and complications of implementation.

I would prefer to integrate the current version of the patch and add functionality for separate type units later. Doing things in that way has the advantage of iterative development. If the patch would be integrated earlier then it would be tested/probed by a bigger amount of people. Also, it might be faster improved by several people. Another thing is that we will have more time to create a good concept for separated type units.

> If we're happy with the approach I think we should land this an iterate on smaller changes that will be much easier to review. One reason I've been so quiet in this review is that it takes a long time to page in everything.

If we`re happy with the current approach I am ready to start the creation of separated patches.
I suggest integrating this version of the patch and do not wait for "several type units" implementation.
"several type units" implementation might be integrated as an addition to this patch.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D96035/new/

https://reviews.llvm.org/D96035