GitLab

In case giga-cage is enabled, for 64bit we can use a bitmap of
super-pages to quickly validate during scanning if a super-page is valid.
The bitmap must consist of only super-pages that correspond to the roots
that have PCScan enabled.

The CL also makes sure that the IsGigaCageEnabled() check is not
performed for each word/scan-range/super-page. To achieve that, it
templatizes scanning routines based on giga-cage presence. Having the
functions parameterized by policies makes sure that there are no hidden
performance costs (e.g. indirect calls).

This improves scanning time on cnn:2020 by ~20%.

Bug: 11297512
Change-Id: I15226e0bfdf3f6d48c39421f4f54cf1aa5bafb4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2624677
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843466}