These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.99 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/userspace-rcu-0.15.6:0/8::gentoo  USE="-static-libs -test -verify-sig" 670 KiB
[ebuild  N     ] dev-util/lttng-ust-2.12.10:0/2.12::gentoo  USE="-examples -numa" 783 KiB

Total: 2 packages (2 new), Size of downloads: 1453 KiB