1709710 - Indicate when C++ return statements are (in)eligible for NRVO (Named Return Value Optimization)

Status: NEW

(Webtools :: Searchfox, enhancement)

Description

[Andrew Sutherland [:asuth] (he/him)]

The Clang AST exposes a getNRVOCandidate getter on the return statement. Sema::computeNRVO does a unification loop where it sets the value to null if any of the returns have a differing NRVO candidate.

Disclaimers:

• I haven't checked when the Sema pass happens relative to our clang indexer plugin.
• I have no reason to believe a non-null NRVO is a guarantee that the optimization definitely happens, but I think there are c++17 things that maybe could require that?

UX-wise, this would probably want to start out life as something in the super navigation panel and not impact the code display. (Although one could imagine some kind of performance lens/overlay in a distant utopian future where it notices from coverage that the return path is potentially hot and an expensive thing is returned that's not NRVO eligible.)