[llvm] [SampleFDO] Stale profile call-graph matching (PR #95135)

[Lei Wang via llvm-commits]

wlei-llvm wrote:

> Does the algorithm need to be iterative? For instance, at top level we have profile function 'foo' calling profile function bar, and IR function 'foo_new' calling IR function 'bar_new'. Can the algorithm recursively match bar with bar_new? If yes, perhaps add a test case.

It works to handle the recursive function matching. It's not strictly iterative but process the functions in a top-down order and the callee's processing can reuse the caller's matching result.  For that example, say the top-down order is 
`main` --> `foo_new` -->`bar_new`
It first process main, and run matching on main's callee sequences(which includes `foo_new`), it identifies `foo_new` --> `foo`, Note that main's process is done and return,(doesn't recursively process callee in main's process)
Then it start a new instance to process `foo_new`, which is found to match `foo` and then it run on its callee sequences matching to identifies `bar_new` --> `bar`

The tricky part here is when a function is top-level function, right now the reader doesn't load the matched profile(which is unused), we need some work for this. I will add a test for non-top-level profile.

 





https://github.com/llvm/llvm-project/pull/95135