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

[via llvm-commits]

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@@ -19,6 +19,9 @@
 
 namespace llvm {
 
+using Anchor = std::pair<LineLocation, FunctionId>;
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WenleiHe wrote:

nit: instead of defining `Anchor` which is not used by `AnchorMap`, how about `using AnchorList = std::vector<std::pair<LineLocation, FunctionId>>` and not defining a common `Anchor` type? 

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