[PATCH] D55309: ThinLTO: Do not import debug info for imported global constants

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

>From what I'm seeing, I would imagine this may regress debug info quality a bit. In the narrow example given, the DWARF still ends up with a description of 'foo', but without any location/value - though this is the same as if 'foo' was in the same translation unit (looks like LLVM fails to track the removing of the global and replacing everything with a constant - I believe the debug info metadata supports describing such a situation, but it isn't being used here - with or without this new change). SO that's not a regression.

But my concern would be if the global variable was in a different static library - then the user could have the variable imported, internalized, the debug info dropped there (with the patch I'm proposing), but then the original object in that static library may never be linked in (since its symbol is no longer needed) - so the resulting program has no DWARF that describes the variable.

I'd like to test this situation, if it's possible - does ThinLTO implement static library-style semantics? Yep, I was able to test that - didn't seem to be a problem. I guess maybe the linker looked at the object dependencies pre-optimization, rather than post-optimization, so the backend foo.o was still linked in, by the looks of it. I guess that makes sense.

So yeah, maybe there is no debug info loss here?


Repository:
  rL LLVM

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  https://reviews.llvm.org/D55309/new/

https://reviews.llvm.org/D55309