[llvm] [ConstantTime][LLVM] Add llvm.ct.select intrinsic with generic SelectionDAG lowering (PR #166702)

[Simon Tatham via llvm-commits]

statham-arm wrote:

@mhaeuser:

> I just would like to gather feedback on how to handle these things at a scale, beyond this specific instruction. Thanks!

This sounds like a thing to ask on Discourse rather than here, so that it will reach a wider audience than the people subscribed to this particular PR. (Not sure whether it should be in the existing thread linked in the PR description, or in a fresh one.)

(I guess your approach would still need some code to lower the constant-time select to some bit-twiddling operations, for platforms that don't have a CT cmov/csel instruction? But that's the kind of question we should take up on Discourse, and leave this PR to its own topic.)

https://github.com/llvm/llvm-project/pull/166702