erin.zhu@mongodb.com noticed this show up in some of our query stats profiles while investigating perf changes caused by SERVER-79736. I don't think there's any reason we need to go into "Date_t::now()" to populate this variable. Definitely we shouldn't need to for the purposes of reporting query stats. But also in general we may be able to share a clock read from the CurOp object or something rather than re-read the clock which can involve a mutex for a VectorClock.

Specifically in cmd_with_let_shape.cpp in makeDummyExpCtx, it ends up calling generateRuntimeConstants in variables.cpp where it takes the VectorClock mutex. Actually, this is the path as of SERVER-79736, looks like it has changed since then but I assume its doing something similar.