1433171 - Investigate /d2guardswtablesuppress flag in MSVC 15.5.3

Status: RESOLVED WONTFIX

(Core :: Security, defect, P5)

Description

[Tom Ritter [:tjr] (OOTO until 4/30 at least)]

MSVC just put out an undocumented /d2guardswtablesuppress flag which implements switches without jump tables, removing some indirect calls. This has benefits for Spectre and CFG.

Try run: https://treeherder.mozilla.org/#/jobs?repo=try&revision=752b951751a321e05fd5b3451ff467abebe76d16

Comment 1

[Tom Ritter [:tjr] (OOTO until 4/30 at least)]

Attachment: Bug 1433171 Do a test run with d2guardswtablesuppress

Review commit: https://reviewboard.mozilla.org/r/215666/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/215666/

Comment 2

[Tom Ritter [:tjr] (OOTO until 4/30 at least)]

Perf results are in: https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=try&newRevision=752b951751a321e05fd5b3451ff467abebe76d16&framework=1&selectedTimeRange=172800

Kind of a mixed bag. There are a few small wins (mostly from upgrading the compiler I believe), similar to guardspecload in Bug 1429807. But there are a few sizable losses (4-11%) on some tests. 

And then there's the CRAZY regressions (40%) on tp6 google.

Comment 3

[Luke Wagner [:luke]]

It would be interesting to enable this and see what it does to JS performance when the JITs are disabled (via javascript.options.ion/baselinejit = false) thus measuring interpreter perf, which is one big switch in a loop.

Comment 4

[Tom Ritter [:tjr] (OOTO until 4/30 at least)]

We don't ship msvc builds anymore.