1949849 - Add a dedicated cast MIR node

Status: NEW

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

Description

[Ryan Hunt [:rhunt]]

For a ref.cast instruction we generate a control flow graph like:

MTest (MWasmRefTest)
|                     \
|                      \
MWasmTrap        Fallthrough...

This seems to give our register allocator a difficult time and results in a lot of spilling across what should just be a side exit. We shoould just fold this all into a dedicated MIR node.

Comment 1

[Ryan Hunt [:rhunt]]

Attachment: Bug 1949849: wasm: Add MWasmRefCast(Abstract, Concrete) nodes. r=rhunt

Copy the RefIsSubtypeOf nodes and create dedicated cast nodes.
The cast nodes return the value so that casted values have the
proper dependency relationship and can't get re-ordered past
the cast.

Comment 2

[Ryan Hunt [:rhunt]]

Attachment: Bug 1949849: wasm: Rename 'RefIsSubtypeOf' to 'RefTest' in MIR for symmetry. r=rhunt

Comment 3

[Ben Visness [:bvisness]]

Attachment: Bug 1949849: wasm: Convert MWasmTrapIfNull to MWasmRefAsNonNull. r=rhunt