[llvm] [PGO] Add ProfileInjector and ProfileVerifier passes (PR #147388)

[David Li via llvm-commits]

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+; Test that prof-verify does not modify existing metadata (incl. "unknown")
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david-xl wrote:

Whether overriding unknown MD_prof should probably be guarded by a flag. There are cases the pass can not do a sophisticated weight propagation to infer weight for new branches, but the prof injection pass can.

https://github.com/llvm/llvm-project/pull/147388