[Dotgnu-libjit] performance of conditionals

[Paul Brannan]

I have a conditional in which one case is many more times likely to
occur than the other case.  Currently the implementation does this:

      branch_if_not(cond, L1)
      <true case>
      branch(L2)
  L1: <false case>
  L2: <remainder of code>
      ...
      return

I have considered implementing it like this instead:

      branch_if_not(cond, L1)
      <true case>
  L2: <remainder of code>
      ...
      return
  L1: <false case>
      branch(L2)

thus avoiding the branch for the usual case.

I'm not a low-level guru, so I'm curious how in general this sort of
refactoring affects performance.

I would write a benchmark, but I'm not sure how to write it in such a
way that it would necessarily reflect real-world performance.

Thoughts?

Paul