Meaning of "taken" for IF instructions

[kripken]

The spec says:

A Branch Hint is a code metadata item with format branch_hint.

It can only be attached to BRIF and IF instructions.

Its payload indicates whether the branch is likely or unlikely to be taken.

For br_if the meaning is clear I think, but for if I am less sure:

..condition..
if
  ..A..
else
  ..B..
end

If the condition is true then we reach A. That means we do not branch, since A is the basic block right after the condition. Should the hint be false if A is likely - is this code fragment correct?

(@metadata.code.branch_hint "\00")
if
  ..very likely to be reached..
else
  ..
end

OTOH, maybe entering A is considered a branch? Technically a VM might branch to get there. And, if A is "branching" then IF and BRIF hints behave the same wrt their conditions (true condition === branch).

The underlying confusion for me is that BRIF has "branch" in the name - it branches if the condition is true. But IF is a control flow structure - is entering it a branch, or avoiding it, or reaching the else?

Anyhow, to clarify this, perhaps

• If the hint in the last code fragment should be 0, the spec could mention "for IF, a branch is considered taken if the condition is FALSE; for BRIF, if the condition is TRUE"
• Or, if the hint should be 1, a way to unify the text could be "the branch hint refers to the likelihood of the condition being TRUE (for IF or BRIF)"
• Either way, examples in the overview could be helpful.

[yuri91]

For the record, the meaning currently encoded in the various implementations is that "likely" means "likely to go into the "if" branch (so, A).

It's true that the wording could be clearer, and I like the framing of focusing on the condition being true or false.

So something like your proposed "the branch hint refers to the likelihood of the condition being TRUE".

I am off this week but I will look into it when I am back.

PRs to improve the overview are welcome.

[kripken]

Thanks for the clarification @yuri91 , I opened #36 now.