tree c844defa542048fdc8c0920da5cbb4b61c941ed0
parent 1b0f22ec57d7b2ee354e7c59e0b6b3ba97680188
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> 1789560707 -0700

Header check: select files from the existing file map

Build the list of files to check by filtering the complete file map.
This avoids rebuilding a second map and repeating the work to merge
each target's source, public and generated file metadata.

Derive the targets for reachability precomputation from the selected
files, so targets without eligible files do not get caches. Add a test
for this selection.

Chromium `gn gen --check`, medians of five round-robin rounds:
  Mac (M4 Max):    3.16 s -> 3.07 s
  GCE c4d-384:     5.96 s -> 5.80 s
  Intel 13900KS:   3.42 s -> 3.24 s

CPU time (c4d-standard-384):
  User:  40.0 s -> 39.6 s (-1%)
  Sys:   53.0 s -> 45.4 s (-14%)

Heap stats:
  Allocs (count):  55.16 M -> 54.24 M (-2%)
  Heap (total):    25.58 GB -> 24.93 GB (-3%)
  Heap (peak):      5.74 GB ->  5.47 GB (-5%)

Change-Id: Iaa4971421bf860d9453dc4ebfa5fd65452a1980c
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/26340
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Philipp Wollermann <philwo@google.com>
Reviewed-by: Matt Stark <msta@google.com>