commit 25b1dd30a912e71e8c0094c1dd53e5af9fca10ff
author Brandon Castellano <bcastell@google.com> Mon Feb 03 09:41:39 2025 -0800
committer CQ Bot <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Feb 03 09:41:39 2025 -0800
tree bd9bad9cd701785ce5b6c117ee155b1a471040c9
parent 8f82d5dc64ef9b6e890bc0da2e55535cd525b197

[vfs][cpp] Allow in-place construction of node attributes

Refactor internal wire table builder so that we can eliminate extra
copies of node attribute data on the stack. Previously, the result of
calling Vnode::GetAttributes was required to be stored on the stack, as
it was assigned to an already constructed object. It also required
unpacking the `zx::result` variant, which further complicated elision
efforts.

This should provide minor performance improvements to the GitStatus and
StatPath benchmarks for memfs and f2fs.

By instead calling Vnode::GetAttributes in the constructor of the wire
table builder, we can ensure the compiler can optimize out the extra
copy. See https://godbolt.org/z/59ExM74br for a more generic example
that demonstrates this technique. Many thanks to the reviewers of
https://fxrev.dev/1194315, the discussion there was crucial in
discovering this approach.

Bug: 391921991
Test: No functional change.
Change-Id: I3d1b78df99cc8cbb98204bb06870824879fbf1a2
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1195918
Reviewed-by: Chris Drouillard <cdrllrd@google.com>
Commit-Queue: Brandon Castellano <bcastell@google.com>