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...> approach may not be resilient to code refactoring changes or semantics > changes like branch flipping. We’d like users to be notified about such > changes so that they can keep their profiles up-to-date. > would matching profile with a flipped branch lead to wrong swapping of taken/nontaken weights? thanks, David > > 3). Possibility of offline count inference. We have an experiment that > encodes edges alongside with probes (blocks), so more sophisticated offline > count inference algorithm is possible to further improve profile quality. > Our algorithm researchers...

...the debug-info-based approach may not be resilient to code refactoring changes or semantics changes like branch flipping. We’d like users to be notified about such changes so that they can keep their profiles up-to-date. would matching profile with a flipped branch lead to wrong swapping of taken/nontaken weights? [hongtao] Yes. If user flips the then-else blocks of an if-statement, the current compiler will still apply the profile from the original code which will lead to wrong branch weights. [wenlei] Right, that would lead to wrong weights, which is problematic for line-based approach as it can...

See my answers inline. From: Xinliang David Li <davidxl at google.com> Date: Friday, August 7, 2020 at 7:57 PM To: Wenlei He <wenlei at fb.com> Cc: "llvm-dev at lists.llvm.org" <llvm-dev at lists.llvm.org>, Wei Mi <wmi at google.com>, Hongtao Yu <hoy at fb.com> Subject: Re: [RFC] Context-sensitive Sample PGO with Pseudo-Instrumentation On Fri, Aug 7,