[llvm] [SampleFDO] Improve stale profile matching by diff algorithm (PR #87375)

[via llvm-commits]

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+//===- SampleProfileMatcherTests.cpp - SampleProfileMatcher Unit Tests -----==//
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WenleiHe wrote:

Slight preference to test it with lit rather than unit test. I think we should be able to craft a test case that shows different matching from the new algorithm? 

That way we can also remove the test/debug only APIs. 

https://github.com/llvm/llvm-project/pull/87375