tree 2336e7302db2d9c7f4a4bfffaf6ed02de4d1cc55
parent 9adad59686716319ac6a229d174d9149e21f8e8e
author Philipp Wollermann <philwo@google.com> 1788904689 +0200
committer gn-scoped@luci-project-accounts.iam.gserviceaccount.com <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1789560756 -0700

Header check: defer unrestricted dependency walks

Precompute only the dependency reachability needed to permit includes.
Leave the unrestricted walk, which also follows private dependencies
transitively, to the existing lazy lookup when no permitted path is
found. This avoids building large diagnostic tables for every checked
target.

Use a shared lock for reachability cache hits, taking the exclusive
lock only on a miss.

Chromium `gn gen --check`, medians of five round-robin rounds:
  Mac (M4 Max):     3.13 s -> 2.70 s
  GCE c4d-384:      5.15 s -> 4.22 s
  Intel 13900KS:    3.30 s -> 2.55 s

CPU time (c4d-standard-384):
  User:  38.5 s -> 31.6 s (-18%)
  Sys:   50.2 s -> 33.9 s (-32%)

Heap stats:
  Allocs (count):  54.24 M -> 53.78 M (-1%)
  Heap (total):    24.92 GB -> 19.78 GB (-21%)
  Heap (peak):      5.46 GB ->  3.22 GB (-41%)

Change-Id: Idbd45609b60d465f78b240db93a33695af34c131
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/26342
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Philipp Wollermann <philwo@google.com>
Reviewed-by: Matt Stark <msta@google.com>