1949075 - Use 'final' when optimizing cast codegen

Status: RESOLVED FIXED

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

Description

[Ryan Hunt [:rhunt]]

A struct or array type can be 'final' and not have any declared subtypes. This means that if we're casting to a type that is final, we only need to emit a type 'equality' check and can skip the 'supertype' vector check.

Comment 1

[Ryan Hunt [:rhunt]]

Instead of doing this check here [1] we could just do a comparison for if the value we're casting has the exactly correct STV.

[1] https://searchfox.org/mozilla-central/rev/27583d5afd9beea3a7551f35470cf188de1d368c/js/src/jit/MacroAssembler.cpp#6845-6848

Comment 2

[Ben Visness [:bvisness]]

Attachment: Bug 1949075: Use final-ness in wasm subtype checks. r=rhunt

Final types can have no subtypes, and therefore when casting to them it
is sufficient to do a simple equality check.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cff9edcdf174
Use final-ness in wasm subtype checks. r=rhunt

Comment 4

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/cff9edcdf174