1488205 - Enable reftypes + repurpose the --wasm-gc flag / about:config option for the "gc" feature

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, enhancement, P3)

Description

[Lars T Hansen [:lth]]

When these things are in place or are jointly landable with the present bug:

- stack maps + stack scanning
- no more suppression of gc when wasm frames are active
- auto-selection of baseline compiler for wasm content that uses gc

then we should no longer be using the gcTypesConfigured flag and we can remove the --wasm-gc flag from the shell and the javascript.options.wasm_gc flag from the browser.

Comment 1

[Lars T Hansen [:lth]]

Does not block milestone 1 since it requires Ion stack maps and those are not part of milestone 1.

Comment 2

[Lars T Hansen [:lth]]

I actually don't think removing --wasm-gc requires Ion stack maps...  I think that all it requires is that when we see the gc_feature_opt_in header in content, that content is compiled with baseline and without tiering.  And then once Ion has stack maps and the reftypes instructions, we will no longer require gc_feature_opt_in for reftypes content, only for content not supported by Ion (struct types).

Comment 3

[Lars T Hansen [:lth]]

Another note: We probably should not remove --wasm-gc, but we should repurpose it so that it enables struct types, once reftypes land for good and we don't require --wasm-gc or gc_feature_opt_in for reftypes.

Comment 4

[Lars T Hansen [:lth]]

Attachment: bug1488205-enable-ion-for-gc.patch

Hacky patch to enable gc content for ion, may need additional work.

Comment 5

[Lars T Hansen [:lth]]

Poaching, it's a good Friday project...

Comment 6

[Lars T Hansen [:lth]]

Attachment: Bug 1488205 - Remove gc_feature_opt_in from reftypes-only tests. r?jseward

Comment 7

[Lars T Hansen [:lth]]

Attachment: Bug 1488205 - Repurpose the --wasm-gc switch for GC. r?jseward

Depends on D21691

Comment 8

[Lars T Hansen [:lth]]

Those two patches sit on top of Julian's patch for Ion stack maps, and together they should be enough to:

• make the reftypes proposal depend only on ENABLE_WASM_REFTYPES being enabled, not any command-line switch
• remove the need for the gc_feature_opt_in header in content that uses only the reftypes features
• make the --wasm-gc switch enable only the experimental GC features, provided ENABLE_WASM_GC is defined

Once these land, reftypes will be enabled by default on Nightly.

The most surprising change here is possibly to wasm/gc/directives.txt, where I removed the configuration "--wasm-gc --wasm-compiler=ion". This is now a meaningless configuration (it will always fail) because --wasm-gc means "the GC features" and not "reftypes + GC".

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/80c1ab6a0f32
Remove gc_feature_opt_in from reftypes-only tests.  r=jseward
https://hg.mozilla.org/integration/mozilla-inbound/rev/8085449bd426
Repurpose the --wasm-gc switch for GC. r=jseward

Comment 10

[Arthur Iakab [arthur_iakab]]

https://hg.mozilla.org/mozilla-central/rev/80c1ab6a0f32
https://hg.mozilla.org/mozilla-central/rev/8085449bd426