1331414 - Make it possible to disable some debug checks

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect, P3)

Description

[Hannes Verschore [:h4writer]]

One of the issues of running debug builds is the speed. The jit engine is doing a lot of tests (AssertBasicXXX and emitDebugResultChecks) which decrease the speed of JS code enormously. As a result we cannot encourage somebody to run a debug build when encountering an issue. Or run it ourself to generate more data.

In this bug I want to add a check that disables most of the slow checks dynamically in about:config. That should make it possible for us to run debug builds again for testing.

The patch I will attach adds in about:config
javascript.options.jit.fullDebugChecks

By setting that to false we will only run the AssertBasicGraph at the end. Not after every pass. And we will not execute emitDebugResultChecks.

Comment 1

[Hannes Verschore [:h4writer]]

Attachment: Patch

Comment 2

[Jan de Mooij [:jandem]]

Comment on attachment 8827208 [details] [diff] [review]
Patch

Review of attachment 8827208 [details] [diff] [review]:
-----------------------------------------------------------------

Thanks for adding this. After we land this, it would be really interesting to compare 2 Try pushes (with this option enabled vs disabled), to see if it speeds up test runs (jit-tests, jsreftests, mochitests in particular). I would also be happy to do that.

::: js/src/jit/IonAnalysis.cpp
@@ +2699,3 @@
>  {
>  #ifdef DEBUG
> +    if (!JitOptions.fullDebugChecks && !force)

We should also add this check to the #ifdef DEBUG integrity.record() and integrity.check() calls in Ion.cpp, as that also does a lot of extra work in debug builds.

There's similar code for RegisterAllocator_Stupid that we can't disable (it's used even in opt builds), but it doesn't matter as we don't use that allocator.

::: modules/libpref/init/all.js
@@ +1251,5 @@
>  #endif
>  pref("javascript.options.throw_on_asmjs_validation_failure", false);
>  pref("javascript.options.ion.offthread_compilation", true);
> +#ifdef DEBUG
> +pref("javascript.options.jit.fullDebugChecks", true);

s/fullDebugChecks/full_debug_checks/ to match the other file.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/dbf9a55f1101
Adding javascript.options.jit.full_debug_checks in about:config for people that want to use debug builds for surfing with less slowdown, r=jandem

Comment 4

[Hannes Verschore [:h4writer]]

When setting this jit-tests improved from 330s to 300s locally

Comment 5

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

Backed out for unused variable 'fullJitDebugChecks' at XPCJSContext.cpp:1452:

https://hg.mozilla.org/integration/mozilla-inbound/rev/f3de7f37c56ee9dd96af01a97099551f13e1dc82

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&revision=dbf9a55f110102ab503c387d2d7009b36a26b052
Failure log: https://treeherder.mozilla.org/logviewer.html#?job_id=73681431&repo=mozilla-inbound

[task 2017-02-01T21:17:35.984804Z] 21:17:35     INFO -  In file included from /home/worker/workspace/build/src/obj-firefox/js/xpconnect/src/Unified_cpp_js_xpconnect_src0.cpp:56:0:
[task 2017-02-01T21:17:35.984907Z] 21:17:35     INFO -  /home/worker/workspace/build/src/js/xpconnect/src/XPCJSContext.cpp: In function 'void ReloadPrefsCallback(const char*, void*)':
[task 2017-02-01T21:17:35.984994Z] 21:17:35     INFO -  /home/worker/workspace/build/src/js/xpconnect/src/XPCJSContext.cpp:1452:10: error: unused variable 'fullJitDebugChecks' [-Werror=unused-variable]
[task 2017-02-01T21:17:35.985061Z] 21:17:35     INFO -       bool fullJitDebugChecks = Preferences::GetBool(JS_OPTIONS_DOT_STR "jit.full_debug_checks");
[task 2017-02-01T21:17:35.985095Z] 21:17:35     INFO -            ^
[task 2017-02-01T21:17:35.985136Z] 21:17:35     INFO -  cc1plus: all warnings being treated as errors
[task 2017-02-01T21:17:35.985201Z] 21:17:35     INFO -  /home/worker/workspace/build/src/config/rules.mk:1012: recipe for target 'Unified_cpp_js_xpconnect_src0.o' failed
[task 2017-02-01T21:17:35.985251Z] 21:17:35     INFO -  gmake[5]: *** [Unified_cpp_js_xpconnect_src0.o] Error 1

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/3d5e5df1bce2
Adding javascript.options.jit.full_debug_checks in about:config for people that want to use debug builds for surfing with less slowdown, r=jandem

Comment 7

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/3d5e5df1bce2

Comment 8

[Hannes Verschore [:h4writer]]

I have been running this happily for two days. Debug builds now don't suck that much anymore! (With these checks disabled).