rustc: Start a custom cabi module for wasm32 #48959
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It actually was already using the `cabi_asmjs` module but that was by accident, so route the new `wasm32-unknown-unknown` target to a new `cabi_wasm32` module. The first entries in this module are to use `signext` and `zeroext` for types that are under 32 bytes in size Closes rust-lang-nursery/rust-wasm#88
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r? @cramertj (rust_highfive has picked a reviewer for you, use r? to override) |
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r? @eddyb I think this is the first time I've attempted to manufacture new cabi code from scratch, so it likely isn't right! (the current state is modeled after asmjs's) |
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@bors r+ |
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📌 Commit 74f5dd0 has been approved by |
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| fn classify_ret_ty<'a, 'tcx>(_cx: &CodegenCx<'a, 'tcx>, ret: &mut ArgType<'tcx>) { | ||
| ret.extend_integer_width_to(32); | ||
| } |
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This doesn't do the aggregate to indirect conversion anymore that the asm.js C ABI did: https://github.com/alexcrichton/rust/blob/74f5dd07cff8dba348f91cfef4df5242ab33a311/src/librustc_trans/cabi_asmjs.rs#L20-L33
However looking at how the C ABI for wasm is implemented in clang, it seems to still do it: https://github.com/llvm-mirror/clang/blob/master/lib/CodeGen/TargetInfo.cpp#L759-L775
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Ah yeah TBH I have very little clue what ABI-related code is doing...
Seems fine though for us to match clang! Until there's an "official ABI" though this'll probably be a game of cat and mouse.
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"Seems fine though for us to match clang!"
I'm a bit confused by that wording. What I'm saying is that we don't match clang anymore with this PR, so shouldn't we include the aggregate code as well to properly match it again?
It seems to be the same as the asm.js one, so we can just copy the code from there / call it.
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Er sorry, what I mean is that it seems fine to add. It won't have any effect today anyway as you can't intermingle wasm32-unknown-unknown and C yet so I'm hoping that we can fix this with a test in the future. (I'm also hesitant to add things that I don't personally understand in my own PRs)
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Well it also affects everyone who is calling an exported function from JS / a wasm environment. However I guess we don't really give any guarantees how structs are represented there anyway, so I guess it's fine to wait on the C ABI settling.
Maybe we should open an issue about this though? Otherwise we might forget about this disparity.
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Yeah with a lack of a spec about an ABI returning any sort of aggregate or non-integer/float is sort of "best effort" today anyway
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Also I have a question. Does this only affect the C ABI or also the Rust ABI? Cause afaict the Rust ABI doesn't need it, and it would probably have a performance impact if it did. |
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@CryZe AFAIK the files here only affect the C ABI, not internal Rust functions |
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@bors: rollup |
rustc: Start a custom cabi module for wasm32 It actually was already using the `cabi_asmjs` module but that was by accident, so route the new `wasm32-unknown-unknown` target to a new `cabi_wasm32` module. The first entries in this module are to use `signext` and `zeroext` for types that are under 32 bytes in size Closes rust-lang-nursery/rust-wasm#88
It actually was already using the
cabi_asmjsmodule but that was by accident,so route the new
wasm32-unknown-unknowntarget to a newcabi_wasm32module.The first entries in this module are to use
signextandzeroextfor typesthat are under 32 bytes in size
Closes rust-lang-nursery/rust-wasm#88