rustc_target/callconv/
x86_win64.rs

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use rustc_abi::{BackendRepr, Float, Primitive};

use crate::abi::call::{ArgAbi, FnAbi, Reg};
use crate::spec::HasTargetSpec;

// Win64 ABI: https://docs.microsoft.com/en-us/cpp/build/parameter-passing

pub(crate) fn compute_abi_info<Ty>(_cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<'_, Ty>) {
    let fixup = |a: &mut ArgAbi<'_, Ty>| {
        match a.layout.backend_repr {
            BackendRepr::Uninhabited | BackendRepr::Memory { sized: false } => {}
            BackendRepr::ScalarPair(..) | BackendRepr::Memory { sized: true } => {
                match a.layout.size.bits() {
                    8 => a.cast_to(Reg::i8()),
                    16 => a.cast_to(Reg::i16()),
                    32 => a.cast_to(Reg::i32()),
                    64 => a.cast_to(Reg::i64()),
                    _ => a.make_indirect(),
                }
            }
            BackendRepr::Vector { .. } => {
                // FIXME(eddyb) there should be a size cap here
                // (probably what clang calls "illegal vectors").
            }
            BackendRepr::Scalar(scalar) => {
                // Match what LLVM does for `f128` so that `compiler-builtins` builtins match up
                // with what LLVM expects.
                if a.layout.size.bytes() > 8
                    && !matches!(scalar.primitive(), Primitive::Float(Float::F128))
                {
                    a.make_indirect();
                } else {
                    a.extend_integer_width_to(32);
                }
            }
        }
    };

    if !fn_abi.ret.is_ignore() {
        fixup(&mut fn_abi.ret);
    }
    for arg in fn_abi.args.iter_mut() {
        if arg.is_ignore() && arg.layout.is_zst() {
            // Windows ABIs do not talk about ZST since such types do not exist in MSVC.
            // In that sense we can do whatever we want here, and maybe we should throw an error
            // (but of course that would be a massive breaking change now).
            // We try to match clang and gcc (which allow ZST is their windows-gnu targets), so we
            // pass ZST via pointer indirection.
            arg.make_indirect_from_ignore();
            continue;
        }
        fixup(arg);
    }
    // FIXME: We should likely also do something about ZST return types, similar to above.
    // However, that's non-trivial due to `()`.
    // See <https://github.com/rust-lang/unsafe-code-guidelines/issues/552>.
}