compiler/rustc_target/src/callconv/x86_win64.rs

use crate::abi::call::{ArgAbi, FnAbi, Reg};
use crate::abi::{Abi, Float, Primitive};
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.abi {
            Abi::Uninhabited | Abi::Aggregate { sized: false } => {}
            Abi::ScalarPair(..) | Abi::Aggregate { 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(),
            },
            Abi::Vector { .. } => {
                // FIXME(eddyb) there should be a size cap here
                // (probably what clang calls "illegal vectors").
            }
            Abi::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() {
            // x86_64-pc-windows-gnu doesn't ignore ZSTs.
            if cx.target_spec().os == "windows"
                && cx.target_spec().env == "gnu"
                && arg.layout.is_zst()
            {
                arg.make_indirect_from_ignore();
            }
            continue;
        }
        fixup(arg);
    }
}