Feature: Multi Value

[bushidocodes]

This feature enables a WebAssembly function to return a tuple of values. When writing WebAssembly by hand, I've found this to be a helpful way to return an (i32, i32) fat pointer to a string or static array of values stored in linear memory.

I am unclear how one can do this with C via WASI-SDK. I've seen code examples that have suggested to me that rightmost arguments can be tagged to be returned as part of a multi-value return. See the C header for WASI itself as an example.

Reference: https://github.com/WebAssembly/multi-value

[bushidocodes]

pub fn wasm_func_type_to_llvm_type<'a>(
    ctx: &'a Context,
    f_type: &wasmparser::FuncType,
) -> &'a llvm::Type {
    let return_count = f_type.returns.len();
    let return_type = if return_count > 1 {
        let rets: Vec<&llvm::Type> = f_type
            .returns
            .into_iter()
            .map(|e| wasm_type_to_llvm_type(ctx, *e))
            .collect();
        StructType::new(ctx, &*rets.into_boxed_slice(), false).to_super()
    } else if return_count == 0 {
        <()>::get_type(ctx)
    } else {
        wasm_type_to_llvm_type(ctx, f_type.returns[0])
    };
    let mut params: Vec<&llvm::Type> = Vec::new();
    for t in &*f_type.params {
        params.push(wasm_type_to_llvm_type(ctx, *t))
    }

    llvm::FunctionType::new(return_type, &params).to_super()
}