[PATCH] D134456: [PGO] Consider parent context when weighing branches with likelyhood.

[Wenlei He via Phabricator via cfe-commits]

wenlei added a comment.

There's also subtle difference between different variants of PGO. For instrumentation PGO where profile quality is higher, profile counts always take precedence. But for sampling PGO (AutoFDO, CSSPGO), it tries to not overwrite any existing branch weights, which means the weights derived from hints earlier are honored. But there's count smoothing algorithm that try to make make CFG counts consistent, which may occasionally overwrite some branch weights that seem really off based on surround count/flow.

The current default looks more like a hint rather than a directive..


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https://reviews.llvm.org/D134456