The code is clearly not branchless as written, and relies on non-trivial optimizations for it to happen.
Just write it correctly to begin with.
It's easy, just run all the instructions from all branches, and select the output you want based on conditionals.
I thought you said it would be branchless.
https://en.wikipedia.org/wiki/Branch_(computer_science)
a jump is one kind of branch, but branch describes more things than just jumps
The code is clearly not branchless as written, and relies on non-trivial optimizations for it to happen.
Just write it correctly to begin with.