1956768 - Possible optimization bug in WasmGC implementation of Firefox

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, defect, P1)

Description

[Martin Kustermann]

Attachment: jsshell_issue.tar.gz

Steps to reproduce:

Using firefox shell to run a WasmGC program

```% third_party/firefox_jsshell/js --version                                                          
JavaScript-C136.0

% third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js $PWD/out.O4.mjs $PWD/out.O4.wasm

This program runs a benchmark for somewhat more than 2 seconds and prints the results

See the attached files for reproduction (I didn't include the jsshell binaries as those are big and should be available from https://archive.mozilla.org/pub/firefox/candidates/)

Actual results:

Running this benchmark seems to be flaky in firefox js shell

Sometimes it completes within 400 ms - which shouldn't be possible as the benchmark itself has a measurement period of 2+ seconds.

% third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js $PWD/out.O4.mjs $PWD/out.O4.wasm
third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js    0.44s user 0.05s system 121% cpu 0.400 total
%

Sometimes the benchmark seems to run for the expected time but doesn't print anything:

% third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js $PWD/out.O4.mjs $PWD/out.O4.wasm
third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js    2.27s user 0.12s system 105% cpu 2.258 total
% 

and sometimes it runs normall

% third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js $PWD/out.O4.mjs $PWD/out.O4.wasm
JsonChunkedUtf8RoundTrip(RunTime): 4680.0 us.
third_party/firefox_jsshell/js $PWD/pkg/dart2wasm/bin/run_wasm.js    2.67s user 0.14s system 106% cpu 2.644 total
%

Expected results:

It should always run for 2+ seconds and print

JsonChunkedUtf8RoundTrip(RunTime): XXX us.

Comment 1

[Yury Delendik (:yury)]

https://pernos.co/debug/-od2oY_pNHtYwIymooRklQ/index.html

Comment 2

[Ryan Hunt [:rhunt]]

Attachment: Bug 1956768 - wasm: Do a CanGC string allocation for js-string/fromCharCodeArray. r?yury

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c737a193828e
wasm: Do a CanGC string allocation for js-string/fromCharCodeArray. r=yury

Comment 4

[pstanciu]

https://hg.mozilla.org/mozilla-central/rev/c737a193828e