1690142 - Update irregexp (Feb 2021)

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Iain Ireland [:iain]]

In the most recent TC39 meeting, the capture indices proposal for regular expressions was updated. The update addressed our concerns about performance by gating the creation of capture indices behind a flag.

Now that TC39 has approved a fix to the performance concerns that prevented us from implementing capture indices, I've started implementing that proposal. Although it's not strictly required, because capture indices are implemented outside of irregexp itself, this seems like as good a time as any to pull in the latest version of irregexp.

The set of noteworthy changes is short. Most of the work in irregexp since our last update has been to implement the experimental non-backtracking engine, which is not yet mature enough for us to import. Aside from some whole-engine refactoring, the main changes have been a smattering of small patches to be more explicit about integer conversions.

Comment 1

[Iain Ireland [:iain]]

Attachment: Bug 1690142: Exclude DIR_METADATA in import-irregexp.py r=mgaudet

V8 added a new metadata file that we have no need to import.

Comment 2

[Iain Ireland [:iain]]

Attachment: Bug 1690142: Re-import irregexp r=mgaudet

This patch is the result of running import-irregexp.py.

Depends on D106963

Comment 3

[Iain Ireland [:iain]]

Attachment: Bug 1690142: Update zone shim r=mgaudet

Zone is the V8 equivalent of SM's LifoAlloc. The API was changed to enable data collection about allocations. We don't need the data collection, but we have to update our Zone shim.

Depends on D106964

Comment 4

[Iain Ireland [:iain]]

Attachment: Bug 1690142: Update shim code r=mgaudet

A variety of small updates. Most notable:

1. V8 added support for a safepoint mechanism where concurrent threads can pause for GC. This means that garbage collection can be triggered without heap allocation, so DisallowHeapAllocation was replaced with DisallowGarbageCollection in most places (including all the ones we care about).

2. CompareCharsEqual was added to make string comparison more efficient in code that is only testing for equality and doesn't have to worry about memcmp giving the wrong ordering for two-byte chars on little-endian systems. The implementation is copy-pasted directly from V8.

3. Some code was rewritten upstream to tighten up integer conversions. As part of that change, uc32 (which represents a Unicode char) is now unsigned. (The maximum valid codepoint in Unicode is 0x10FFFF, so signed vs unsigned doesn't generally matter in practice.)

Depends on D106965

Comment 5

[Iain Ireland [:iain]]

Attachment: Bug 1690142: Suppress type-limits errors r=mgaudet

-Werror=type-limits emits an error if a comparison is vacuously true. Upstream irregexp does not compile with -Werror=type-limits, so occasionally irregexp will, for example, assert that an unsigned variable is >= 0. It's not worth upstreaming a patch to remove the trivial assertion every time a case sneaks in; instead, we can just suppress the error in irregexp/moz.build.

Depends on D106966

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5c49a1fc3ed9
Exclude DIR_METADATA in import-irregexp.py r=mgaudet
https://hg.mozilla.org/integration/autoland/rev/391b05257d66
Re-import irregexp r=mgaudet
https://hg.mozilla.org/integration/autoland/rev/6e6fbe10aa30
Update zone shim r=mgaudet
https://hg.mozilla.org/integration/autoland/rev/271750e0dd2e
Update shim code r=mgaudet
https://hg.mozilla.org/integration/autoland/rev/23f91d432267
Suppress type-limits errors r=mgaudet

Comment 7

[Dorel Luca [:dluca]]

https://hg.mozilla.org/mozilla-central/rev/5c49a1fc3ed9
https://hg.mozilla.org/mozilla-central/rev/391b05257d66
https://hg.mozilla.org/mozilla-central/rev/6e6fbe10aa30
https://hg.mozilla.org/mozilla-central/rev/271750e0dd2e
https://hg.mozilla.org/mozilla-central/rev/23f91d432267