[PATCH] D37600: Preserve existing registers when adding pristines to LivePhysRegs

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

When I wrote this I assumed that `addLiveOuts()`/`addLiveIns()` is only called on empty sets looks like I didn't add an `assert()` for that and ifconversion does indeed call it no non-empty sets now. Thanks for tracking this down!

- Can you maintain an optimized code path that avoids the creation of an extra LivePhysRegs instance in the common case where the set is empty?
- We probably want the same fix (or an `assert(empty())`) in LiveRegUnits as well.


Repository:
  rL LLVM

https://reviews.llvm.org/D37600