[WiP] Initial changes to support wasm64 in emcc

[aardappel]

No description provided.

[welcome]

Thank you for submitting a pull request! If this is your first PR, make sure to add yourself to AUTHORS.

[sbc100]

Wow! Is this really your first emscripten change! How exciting for you :)

[aardappel]

This is unfinished, but useful to maybe have a quick look to see what I am all doing wrong ;)

In particular, the libc changes probably shouldn't land as-is, but they indicate what was required to make this work.

[sbc100]

Looks mostly great!

What do we think about that name "memory64" vs "wasm64" (which is used in the llvm world)?

[aardappel]

@sbc100 in the future, we're going to have a world where a single Wasm module can potentially access both a 32-bit and 64-bit memory at the same time, and load/store operations just match the memory they access. Thus, from a Wasm perspective, this is a memory property, not an "architecture". We have already used the term "memory64" thru-out the WABT and Binaryen implementations. To verify wether a load/store is correct, these tools look up the associated memory.

Of course, LLVM doesn't understand such a concept, and thinks in terms of architectures that hold for the entire program, so there "wasm64" is more appropriate. I personally like this term better also, since 99% of programmers are not going to understand the subtleties around Wasm memories. But it is a useful distinction for us.

[sbc100]

sgtm!

[kripken]

Exciting stuff!

[kripken]

lgtm minus minor comments.

[sbc100]

lgtm % a couple more comments!