1657614 - Make ObjLiteralStencil initialization in BytecodeEmitter more robust

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Ted Campbell [:tcampbell]]

As pointed out in Bug 1657353 review process, the filling in the ObjLiteralStencil in-place in the compilationInfo is a bit of a footgun if there ever was a resize of the vector. Refactoring the code so that compilationInfo isn't available to the parts filling in the stencil would help here.

Another option would be to build on stack and then move to the array, but the ObjLiteralStencil is ~224B right now so this isn't very ideal.

Comment 1

[Tooru Fujisawa [:arai]]

To achieve bug 1678449, ObjLiteralStencil shouldn't contain Vector:

• use stack-allocated ObjLiteralWriter when emitting object
• when putting it into stencil, copy the code into LifoAlloc, and put the pointer into ObjLiteralStencil, with Span
  it will solve this bug at the same time.

Comment 2

[Tooru Fujisawa [:arai]]

Attachment: Bug 1657614 - Decouple ObjLiteralWriter and ObjLiteralStencil. r?nbp!

ObjLiteralStencil doesn't have to be writable, and the cost of Vector handling
is problematic when decoding.

Decoupled ObjLiteralWriter from ObjLiteralStencil and now ObjLiteralStencil
has a Span that points memory block inside LifoAlloc.
While compiling, the data is copied from ObjLiteralWriter's Vector to LifoAlloc,
and while decoding, the memory is copied from XDR buffer to LifoAlloc.

Depends on D99051

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/aad18f232c51
Decouple ObjLiteralWriter and ObjLiteralStencil. r=nbp

Comment 4

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/aad18f232c51