tree 81ee3b609b5ad3aba95838ae8f7536f676218466
parent 95b0f8fe31a992a33c040bbe3867901335c12762
author David 'Digit' Turner <digit@google.com> 1639742579 +0100
committer GN LUCI <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1728948142 +0000

Do not copy parent build_dependency_files_ in Scope constructors.

SourceFileSet insert operations appear high in performance profiles,
and can be reduced by doing less of them. This is achieved by
ensuring that Scope::build_dependency_files_ only contains the
source files added by a given scope, instead of the union of the
scope itself and of its parents.

A new method Scope::CollectBuildDependencyFiles() is introduced to
compute the final set of source files for users that need it.

Measurements with hyperfine shows that this speeds up `gn gen`
x1.05 with a small Fuchsia build plan (7.2s -> 6,8s). Also
peak RSS goes from 3.78 GiB to 3.58 GiB (200 MiB saved!).

Change-Id: I684b305421ec684e45b02785e70580efa8f1c2ff
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/17880
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: David Turner <digit@google.com>