[wasm] Assert prevents wasm64 codegen

[derek-gerstmann]

Is this assert still valid now that wasm64 / Memory64 is in mainline for emscripten and available in Chrome?

Halide/src/CodeGen_WebAssembly.cpp

Line 411 in b232c0f

user_assert(target.bits == 32) << "Only wasm32 is supported.";

Emscripten ChangeLog:
https://github.com/emscripten-core/emscripten/blob/main/ChangeLog.md#3172---111924

Chrome Status:
https://chromestatus.com/feature/5070065734516736

[abadams]

It's possible there are things in the Halide wasm backend or runtime that assume 32-bit, so it could mean that Halide doesn't support bits != 32, rather than chrome doesn't.

However I can't think of any off the top of my head. Maybe it would work?

[steven-johnson]

The existing code was written for 32 bit and has never been tested with 64 bit. It's probably pretty close to ok but I would be surprised if there aren't some glitches that are present.

…

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