[llvm] [llvm-dwp] turn duplicate dwo id into warning, continue to gen dwp (PR #121193)

[Jinjie Huang via llvm-commits]

Labman-001 wrote:

>  the same file compiled/linked in twice, and the linker discards one but the dwp actions don't know how to do that (if you're using dwp -e you probably wouldn't hit these cases, since the redundant objects would be discarded by the linker)

Yes, the normal duplicate .cpp should be discarded when linking as mentioned. What's interesting here is the real case we met: multiple .a files have the same .o files (which only contain declarations and are linked using whole-archive, I know this is a bit inappropriate), causing the linker to link all the duplicate .o files in the main program. Using llvm-dwp -e <bin> will result in an error in this case because of the duplicate skeletons. So it seems there is a possibility of such skeleton duplication...

> I'm guessing current DWARF consumers don't handle this, and just assume it's a bug/mistake/duplicate skeleton unit if two have the same DWO ID. 

Do we have any thoughts on this? Should we consider skipping the duplicate DWOs and then generating the DWP, or packaging the duplicate DWOs in the DWP (what binutil dwp does), or continue with the current approach of reporting an error and then exiting?


https://github.com/llvm/llvm-project/pull/121193