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Use signext and zeroext argument attributes. #88

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sunfishcode opened this issue Mar 12, 2018 · 2 comments
Closed

Use signext and zeroext argument attributes. #88

sunfishcode opened this issue Mar 12, 2018 · 2 comments

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@sunfishcode
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Rust should use LLVM's signext and zeroext argument attributes for bool/i8/i16/u8/u16 types when targetting WebAssembly, for consistency with LLVM IR generated by clang, and to allow these values to be automatically interpreted by JS.

For example, on this Rust code:

#[no_mangle]
pub extern fn narrow(x: i32) -> i8 {
  x as i8
}
#[no_mangle]
pub extern fn widen(x: i8) -> i32 {
  x as i32
}

Running rustc test.rs --emit llvm-ir --crate-type=cdylib --target=wasm32-unknown-unknown produces:

[...]
define i8 @narrow(i32 %x) unnamed_addr #0 {
[...]
define i32 @widen(i8 %x) unnamed_addr #0 {
[...]

It should have attributes like this:

[...]
define signext i8 @foo(i32 %x) unnamed_addr #0 {
[...]
define i32 @bar(i8 signext %x) unnamed_addr #0 {
[...]
@sunfishcode sunfishcode mentioned this issue Mar 12, 2018
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alexcrichton referenced this issue in alexcrichton/rust Mar 12, 2018
@alexcrichton
rustc: Start a custom cabi module for wasm32
74f5dd0 
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
@alexcrichton alexcrichton mentioned this issue Mar 12, 2018
Merged
@alexcrichton
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Oh nice catch! I've submitted rust-lang/rust#48959 to cover this

@CryZe CryZe mentioned this issue Mar 15, 2018
Closed
kennytm referenced this issue in kennytm/rust Mar 15, 2018
@kennytm
Rollup merge of rust-lang#48959 - alexcrichton:signext, r=eddyb
292c6ca 
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
@alexcrichton
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Fixed in rust-lang/rust#48959

This was referenced Jun 21, 2023
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@alexcrichton @sunfishcode