[PATCH] D43199: [IRMover] Implement name based structure type mapping

[Rafael Avila de Espindola via llvm-commits]

Evgeny Leviant <eleviant at accesssoftek.com> writes:

>> Why do you need ThinLTO to test a type merging feature? Could this use
>> llvm-link?
>
> The specifics of thinlto import is that module is partially  imported to an existing module, while llvm-link imports all source modules to an empty destination module.
> This causes differences in how structure types are processed: thinlto calls addNonOpaque for all structure types in non-empty destination module before 
> actual import is started (see IRMover constructor) and llvm-link calls addNonOpaque(S) during import process when structure S is being imported to the destination
> module. 
>
> As a result structure Foo will not be imported at all if you use llvm-link, because it is isomorphic to previously declared Bar and all references to Foo
> will be replaced by references to Bar in the destination module. This is cool, but I don't think it is usable for thinlto as we're doing partial link.

This suggests that ThinLTO should be changed. It is fine to start with a
non empty module, but it should scan its types so that Foo is found to
be isomorphic to Bar an not imported.

I would also suggest adding a flag to llvm-link to create the Linker
with a given bitcode file. That should allow us to test this with
llvm-link.

Cheers,
Rafael