[PATCH] D71572: [ItaniumCXXABI] Make tls wrappers comdat on Windows

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added inline comments.


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Comment at: clang/lib/CodeGen/ItaniumCXXABI.cpp:2551
+  // actually handle multiple TUs defining the same wrapper.
+  if (CGM.getTriple().isOSWindows() && CGM.supportsCOMDAT() &&
+      Wrapper->isWeakForLinker())
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mstorsjo wrote:
> mstorsjo wrote:
> > rnk wrote:
> > > IMO we should be doing the same thing on ELF, you can see the code pattern used elsewhere:
> > > http://llvm-cs.pcc.me.uk/?q=setComdat
> > > 
> > > Before comdats were made explicit in the IR and we stopped implicitly making comdat groups for odr things on ELF, these wrappers would've been in a comdat group.
> > Ok, so remove the `isOSWindows()` and maybe remove the comment altogether as it isn't windows specific any longer?
> In the current tests, for linux there's explicit checks that these aren't marked as comdat, see e.g. https://github.com/llvm/llvm-project/blob/master/clang/test/CodeGenCXX/cxx11-thread-local.cpp#L208. Is there a specific reason for that, or should it be changed?
The test is intending to check that the wrapper is not in a comdat keyed off the variable. Putting it in a trivial comdat is fine and correct; please update the tests to check that it's in the right comdat, not just that it's in some comdat. (I seem to regularly forget that `weak` / `linkonce` / `weak_odr` / `linkonce_odr` don't actually work as documented any more...)


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  https://reviews.llvm.org/D71572/new/

https://reviews.llvm.org/D71572