tree 1b7453520f9632f5499c499e172eae9493f06756
parent 22b8bd000500b1f8640143d3cc7086d5cbc2c00c
author Philipp Wollermann <philwo@chromium.org> 1782555681 +0900
committer gn-scoped@luci-project-accounts.iam.gserviceaccount.com <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1782710431 -0700

Share ResolvedTargetData across targets in --ide=json

GenerateJSON() builds a description for every resolved target, and
TargetDescBuilder::BuildDescription() constructed a fresh
ResolvedTargetData for each one to compute inherited libs/frameworks.
ResolvedTargetData is a memoizing cache whose lib/framework computation
recurses over the transitive linked-deps subgraph; recreating it per
target threw away all memoization and made the whole pass quadratic.

Add an optional ResolvedTargetData* parameter to
DescBuilder::DescriptionForTarget() and have json_project_writer pass a
single shared instance for all targets. Other callers (command_desc)
keep the previous per-call behavior via the nullptr default.

For a Chromium out/debug tree (31145 targets), "gn gen --ide=json" drops
from ~62.5s to ~2.1s for the JSON phase (total gen 64s -> 3.8s). The
generated 507 MB project.json is byte-identical before and after.

Change-Id: I5480c5145b292221032b5a447f3eeaede6f1c54e
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/23460
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Philipp Wollermann <philwo@google.com>