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

[Duncan P. N. Exon Smith via Phabricator via cfe-commits]

dexonsmith added a comment.

In D134456#3827263 <https://reviews.llvm.org/D134456#3827263>, @aaron.ballman wrote:

> My worry is that parallel attributes will be used as:
>
>   #if __has_cpp_attribute(clang::likely_but_honor_this_one)
>   #define LIKELY [[clang::likely_but_honor_this_one]]
>   #elif __has_cpp_attribute(likely)
>   #define LIKELY [[likely]]
>   #else
>   #define LIKELY
>   #endif

To be clear, I was imagining:

  if (always_false()) [[likely]] [[clang::nopgo]] {
    // ...
  }

where ``nopgo`` might be independently useful for telling clang to ignore any collected PGO data when estimating branch weights in a particular control flow block.

Some users might combine the two into a macro ("always ignore the profile when I say something is likely!"), but I don't think there'd be a cascade.


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https://reviews.llvm.org/D134456