Self-hosting probably makes sense for some of the functions that (can) take a callback argument like replace, but for exec and test we can likely get rid of some overhead by implementing in C++ and optimizing the builtin in the JITs.

The main difficulty is updating the .lastIndex value for global/sticky regular expressions, but that should be doable with CacheIR now.

I started prototyping this for RegExpBuiltinExec, because that's near the bottom of the call stack. Implementing it in C++ is nice so far, it lets us get rid of some layers of abstraction.

I have some WIP patches to port these to C++:

• RegExpBuiltinExec
• RegExpExec
• RegExp_prototype_Exec

Next step is to see how this affects Speedometer.

These can mostly share the same CacheIR code for the fast path. After this there are other self-hosted functions one layer up that we might be able to port to C++ too (RegExpTest, maybe RegExpMatch).

(In reply to Jan de Mooij [:jandem] from comment #2)

• RegExp_prototype_Exec

This one is a bit of a problem because it's sometimes polymorphic. Octane-regexp calls it with a string-or-undefined argument, so my patches regressed our score on that test a lot, and a Speedometer 3 test (I think React-Stockcharts) calls it with an object argument (hard to support because side-effects).

RegExp_prototype_Exec is a small wrapper around RegExpBuiltinExec so let's start with just RegExpBuiltinExec and RegExpExec. This improves our Octane-regexp score by a few hundred points and should be a small win on Speedometer.

We want to reuse this in the next patch.

Also add an isInitialShape fast path to it, which turned out to be missing a check
for is-still-writable.

This is faster than the self-hosted implementation, especially with the JIT
optimizations added in later patches.

IC and Ion code will call the RegExpBuiltinExecMatchRaw and RegExpBuiltinExecTestRaw
functions directly.

Depends on D177504

Usually .exec will be the original RegExp.prototype.exec function, and in that case
we can call RegExpBuiltinExec.

Depends on D177505

Depends on D177506

These are very similar to RegExpMatcher and RegExpTester, except that we have some
additional code for reading/writing lastIndex.

The next patch will remove RegExpTester.

Depends on D177507

Depends on D177508

Speedometer 3 comparison:

https://treeherder.mozilla.org/perfherder/comparesubtest?originalProject=try&newProject=try&newRevision=e3522e541d50b0bfd0b8e2bf7adb2f44a08f2a61&originalSignature=4586009&newSignature=4586009&framework=13&application=firefox&originalRevision=5da365d15093bdec368e2c08e8782a8dc2f78dcc&page=1

Sorting sub-tests by confidence shows a number of high-confidence 2-4% improvements.

Very nice! But huh, Backbone got slower in some places! I was expecting Backbone to benefit the most.

Callers typically pass a constant true/false so we can get rid of a CacheIR guard in this case.

Depends on D177509

Backed out for causing dt failure on browser_script_command_execute_basic.js.

• Push with failures

• Failure log

• Backout link

[task 2023-05-11T16:29:59.036Z] 16:29:59     INFO - TEST-PASS | devtools/shared/commands/script/tests/browser_script_command_execute_basic.js | property 'input'undefined - 
[task 2023-05-11T16:29:59.038Z] 16:29:59     INFO - checking object for property 'result'undefined
[task 2023-05-11T16:29:59.039Z] 16:29:59     INFO - TEST-PASS | devtools/shared/commands/script/tests/browser_script_command_execute_basic.js | property 'type'undefined - 
[task 2023-05-11T16:29:59.040Z] 16:29:59     INFO - Buffered messages finished
[task 2023-05-11T16:29:59.045Z] 16:29:59     INFO - TEST-UNEXPECTED-FAIL | devtools/shared/commands/script/tests/browser_script_command_execute_basic.js | no eval exception - 
[task 2023-05-11T16:29:59.046Z] 16:29:59     INFO - Stack trace:
[task 2023-05-11T16:29:59.046Z] 16:29:59     INFO - chrome://mochikit/content/browser-test.js:test_ok:1584
[task 2023-05-11T16:29:59.047Z] 16:29:59     INFO - chrome://mochitests/content/browser/devtools/shared/commands/script/tests/browser_script_command_execute_basic.js:doEagerEvalWithSideEffectMonkeyPatched:603
[task 2023-05-11T16:29:59.048Z] 16:29:59     INFO - chrome://mochitests/content/browser/devtools/shared/commands/script/tests/browser_script_command_execute_basic.js:null:89
[task 2023-05-11T16:29:59.049Z] 16:29:59     INFO - chrome://mochikit/content/browser-test.js:handleTask:1133
[task 2023-05-11T16:29:59.050Z] 16:29:59     INFO - chrome://mochikit/content/browser-test.js:_runTaskBasedTest:1205
[task 2023-05-11T16:29:59.051Z] 16:29:59     INFO - chrome://mochikit/content/browser-test.js:Tester_execTest:1347
[task 2023-05-11T16:29:59.052Z] 16:29:59     INFO - chrome://mochikit/content/browser-test.js:nextTest/<:1122
[task 2023-05-11T16:29:59.052Z] 16:29:59     INFO - chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:SimpleTest.waitForFocus/<:1056
[task 2023-05-11T16:29:59.056Z] 16:29:59     INFO - TEST-PASS | devtools/shared/commands/script/tests/browser_script_command_execute_basic.js | no helper result - 

(In reply to Iulian Moraru from comment #14)

Backed out for causing dt failure on browser_script_command_execute_basic.js.

This is a devtools eager evaluation failure. The call to (overridden) exec functions in RegExpExec needs to be marked as CallReason::CallContent.

https://hg.mozilla.org/mozilla-central/rev/181d38478102
https://hg.mozilla.org/mozilla-central/rev/1c9a6dc02923
https://hg.mozilla.org/mozilla-central/rev/bf65109b6c41
https://hg.mozilla.org/mozilla-central/rev/68dd64a6dbe8
https://hg.mozilla.org/mozilla-central/rev/9e2a3f04e0ac
https://hg.mozilla.org/mozilla-central/rev/05b3296dcc61
https://hg.mozilla.org/mozilla-central/rev/5ac14c27f807