[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -0,0 +1,98 @@
+; REQUIRES: object-emission
+
+; Make sure the fake use of 'b' at the end of 'foo' causes location information for 'b'
+; to extend all the way to the end of the function.
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OCHyams wrote:

In an ideal world, we'd probably want to also check that not-using fake-uses results in `b` not extending to the end of the function, to prevent rotten green tests. Might be a bit fiddly though. wdyt, is it possible?

https://github.com/llvm/llvm-project/pull/86149