1799971 - Use signal handling for null pointer checks of GC objects in baseline

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, enhancement, P2)

Description

[Ryan Hunt [:rhunt] (on leave until early May)]

We should see if we can eliminate our null-checks for GC operations using our signal handling mechanism.

We currently do something similar to this for call_indirect, where the function we're calling will have InstanceReg = null when the function pointer is null. So we mark the instruction to load the HeapReg from InstanceReg as a potentially trapping instruction [1].

I believe we can just do a similar thing for most of our GC instructions. For all of them we need to emit the trap metadata immediately before the first load that would be done on a potentially null pointer.

[1] https://searchfox.org/mozilla-central/rev/99f83e78415867726a5076a525e4a60840f3be33/js/src/jit/MacroAssembler.cpp#4436

Comment 1

[Yury Delendik (:yury)]

Attachment: Bug 1799971 - Use signal for null GC references checks. r?rhunt

Comment 2

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/e4507c5f89e2