[PATCH] D52893: [ThinLTO] Keep non-prevailing (linkonce|weak)_odr symbols live

[Xin Tong via Phabricator via llvm-commits]

trentxintong added inline comments.


================
Comment at: lib/Transforms/IPO/FunctionImport.cpp:746
+    // later in the EliminateAvailableExternally pass and setting them to
+    // not-live could break downstreams users of liveness information (PR36483)
+    // or limit optimization opportunities.
----------------
trentxintong wrote:
> tejohnson wrote:
> > Are you fixing another instance of PR36483? If not, then the comment should probably be updated to indicate that this is to fix a missed optimization.
> Hi Teresa
> 
> Thank you for the comment. 
> 
> We have some linkonceodr symbols that are included in multiple files, one of the files is compiled to ELF object file directly which makes the ones in the IR object non-prevailing.
> 
> Originally we crashed because the IR level vtable (linkonce_odr linkage) is not prevailing and WPD crashed. This should be prevented by https://reviews.llvm.org/D52175.
> 
> So at this point, this patch is more to improve a missed optimization opportunity than fix a crash. I have the comment "or limit optimization opportunities" in the comment. 
This also applies to other vague odr symbols we see with template functions, etc.


Repository:
  rL LLVM

https://reviews.llvm.org/D52893