1691612 - Add public APIs for CompilationStencil

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Ted Campbell [:tcampbell]]

The js::frontend::CompilationStencil is the main structure for representing parsed JS before it is turned into GC-scripts. To support the various Stencil objectives, we would like a fool-proof abstraction that can be manipulated from Gecko. This bug is about defining that API and resolving footguns.

Comment 1

[Ted Campbell [:tcampbell]]

The CompilationStencil references the following external VM things:

• SharedImmutableScriptData
• ScriptSource
• AsmJS WasmModule

These do not contain GC-things but a lightly coupled to the JSRuntime. These restrictions are minimal and we can reduce over time. In practice though, our domain of sharing would always have a common parent-runtime.

The CompilationStencil itself should have a ref-counting mode. A policy for mutation should be established. For example, if we are delazifying, can we update/append an existing stencil and how should this support threading.

Another important external reference is the XDRBuffer if we decoded the stencil directly from XDR. We should probably make a ref-counted XDRBuffer and have the stencil hold a strong reference if we rely on the data.

Another wrinkle now is the atom-cache that is part of CompilationInput.

Comment 2

[Ted Campbell [:tcampbell]]

A rough design here might look like:

• Add JS::Stencil type in public that is alias of js::frontend::CompilationStencil
• Add refCount field to CompilationStencil
• Add public JS::StencilAddRef / JS::StencilRelease
• Use RefPtrTraits to allow opaque type to call the non-member JS::StencilAddRef
• The public CompileToStencil can then return the already_AddRefed<CompilationStencil>
• Use the js/public/experimental directory for now

The widget/gtk/GRefPtr.h is a rough example of this (where GObject is an opaque type implemented in external library).

Comment 3

[Ted Campbell [:tcampbell]]

Attachment: Bug 1691612 - Simplify the CompilationStencil preparation code. r?arai!

Store the max*DataLength values on the StencilDelazificationSet so that it
can be used for multiple instantiations. Separate out the preparation of the
stencil from the gc-output structure for the same reasons.

Comment 4

[Ted Campbell [:tcampbell]]

Attachment: Bug 1691612 - Add public API for JS::Stencil. r?arai!

Introduce an opaque JS::Stencil type for working with CompilationStencil via
the public API (such as in Gecko).

Depends on D104744

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/4b1348088c24
Simplify the CompilationStencil preparation code. r=arai
https://hg.mozilla.org/integration/autoland/rev/3d32b5d798f4
Add public API for JS::Stencil. r=arai

Comment 6

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/4b1348088c24
https://hg.mozilla.org/mozilla-central/rev/3d32b5d798f4