tree ee9f8e65a62d00cae92f64f7c3f01e86e3f0e472
parent 41942b7e214b6ad3614f31caa5e3281370fef767
author Takuto Ikuta <tikuta@google.com> 1771334072 +0900
committer GN LUCI <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1771339291 -0800

[perf] Cache dependency checks in HeaderChecker

This optimization introduces a thread-safe cache for IsDependencyOf
results in HeaderChecker.

On large projects like Chromium, 'gn gen --check' performs a massive
number of include validations. Many of these involve checking
reachability between the same pairs of targets over and over again. Each
check previously required a full BFS traversal of the dependency graph.

By caching whether target A can depend on target B (and if the path is
publicly permitted), we avoid the vast majority of these expensive
traversals.

Performance on Chromium 'gn gen --check':
- Before: ~125 seconds
- After: ~66 seconds (approx. 47% faster)
- CPU user time reduced from ~16 minutes to ~8 minutes.

Bug: 484862257
Change-Id: Ib46fef088039a145a53f1eb541c27f296a4df3ba
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/21001
Commit-Queue: Takuto Ikuta <tikuta@google.com>
Reviewed-by: David Turner <digit@google.com>