[llvm-branch-commits] [libcxx] [libc++] Add ABI flag to make __tree nodes more compact (PR #147681)

[Louis Dionne via llvm-branch-commits]

https://github.com/ldionne commented:

LGTM but let's A/B measure this to see whether there is a visible impact. I'm especially looking for a regression caused by more expensive pointer chasing since we have to "decode" the pointer now. If we don't see issues with this, I think I'd be OK with making this the new "de facto" ABI for v2 unconditionally.

Also, this obviously needs `pointer_int_pair` to land.

https://github.com/llvm/llvm-project/pull/147681