[PATCH] D86559: [Sema, CodeGen] Allow [[likely]] and [[unlikely]] on labels

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added a comment.

This feels like the wrong approach to me... but I admit that I don't know what the "right" approach might be. (I doubt any right approach exists.)

  if (ch == ' ') [[likely]] {
      goto whitespace;  // A
  } else if (ch == '\n' || ch == '\t') [[unlikely]] {
      goto whitespace;  // B
  } else {
      foo();
  }
  [[likely]] whitespace: bar();  // C

It seems like this patch would basically "copy" the `[[likely]]` attribute from line C up to lines A and B, where it would reinforce the likelihood of path A and (maybe?) "cancel out" the unlikelihood of path B, without actually saying anything specifically about the likelihood of label C (which is surely what the programmer intended by applying the attribute, right?). OTOH, I can't think of any particular optimization that would care about the likelihood of label C. I could imagine trying to align label C to a 4-byte boundary or something, but that wouldn't be an //optimization// on any platform as far as I know.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86559/new/

https://reviews.llvm.org/D86559