[llvm] [RDA] Fix getGlobalUses() to account for redefinitions (PR #78178)

[Dmitry Borisenkov via llvm-commits]

akiramenai wrote:

@sparker-arm Did I get it with that the idea is to construct some MIR in a C++ unit test and call `getGlobalUses()` for it to expose the issue? If we can't find anything better than that, I will return back when I implement this test.

https://github.com/llvm/llvm-project/pull/78178