diff --git a/compiler/rustc_codegen_llvm/src/va_arg.rs b/compiler/rustc_codegen_llvm/src/va_arg.rs
new file mode 100644
index 0000000..22ed4dd
--- /dev/null
+++ b/compiler/rustc_codegen_llvm/src/va_arg.rs
@@ -0,0 +1,205 @@
+use crate::builder::Builder;
+use crate::type_::Type;
+use crate::type_of::LayoutLlvmExt;
+use crate::value::Value;
+use rustc_codegen_ssa::mir::operand::OperandRef;
+use rustc_codegen_ssa::{
+    common::IntPredicate,
+    traits::{BaseTypeMethods, BuilderMethods, ConstMethods, DerivedTypeMethods},
+};
+use rustc_middle::ty::layout::HasTyCtxt;
+use rustc_middle::ty::Ty;
+use rustc_target::abi::{Align, HasDataLayout, LayoutOf, Size};
+
+fn round_pointer_up_to_alignment(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    addr: &'ll Value,
+    align: Align,
+    ptr_ty: &'ll Type,
+) -> &'ll Value {
+    let mut ptr_as_int = bx.ptrtoint(addr, bx.cx().type_isize());
+    ptr_as_int = bx.add(ptr_as_int, bx.cx().const_i32(align.bytes() as i32 - 1));
+    ptr_as_int = bx.and(ptr_as_int, bx.cx().const_i32(-(align.bytes() as i32)));
+    bx.inttoptr(ptr_as_int, ptr_ty)
+}
+
+fn emit_direct_ptr_va_arg(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    llty: &'ll Type,
+    size: Size,
+    align: Align,
+    slot_size: Align,
+    allow_higher_align: bool,
+) -> (&'ll Value, Align) {
+    let va_list_ptr_ty = bx.cx().type_ptr_to(bx.cx.type_i8p());
+    let va_list_addr = if list.layout.llvm_type(bx.cx) != va_list_ptr_ty {
+        bx.bitcast(list.immediate(), va_list_ptr_ty)
+    } else {
+        list.immediate()
+    };
+
+    let ptr = bx.load(va_list_addr, bx.tcx().data_layout.pointer_align.abi);
+
+    let (addr, addr_align) = if allow_higher_align && align > slot_size {
+        (round_pointer_up_to_alignment(bx, ptr, align, bx.cx().type_i8p()), align)
+    } else {
+        (ptr, slot_size)
+    };
+
+    let aligned_size = size.align_to(slot_size).bytes() as i32;
+    let full_direct_size = bx.cx().const_i32(aligned_size);
+    let next = bx.inbounds_gep(addr, &[full_direct_size]);
+    bx.store(next, va_list_addr, bx.tcx().data_layout.pointer_align.abi);
+
+    if size.bytes() < slot_size.bytes() && &*bx.tcx().sess.target.target.target_endian == "big" {
+        let adjusted_size = bx.cx().const_i32((slot_size.bytes() - size.bytes()) as i32);
+        let adjusted = bx.inbounds_gep(addr, &[adjusted_size]);
+        (bx.bitcast(adjusted, bx.cx().type_ptr_to(llty)), addr_align)
+    } else {
+        (bx.bitcast(addr, bx.cx().type_ptr_to(llty)), addr_align)
+    }
+}
+
+fn emit_ptr_va_arg(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+    indirect: bool,
+    slot_size: Align,
+    allow_higher_align: bool,
+) -> &'ll Value {
+    let layout = bx.cx.layout_of(target_ty);
+    let (llty, size, align) = if indirect {
+        (
+            bx.cx.layout_of(bx.cx.tcx.mk_imm_ptr(target_ty)).llvm_type(bx.cx),
+            bx.cx.data_layout().pointer_size,
+            bx.cx.data_layout().pointer_align,
+        )
+    } else {
+        (layout.llvm_type(bx.cx), layout.size, layout.align)
+    };
+    let (addr, addr_align) =
+        emit_direct_ptr_va_arg(bx, list, llty, size, align.abi, slot_size, allow_higher_align);
+    if indirect {
+        let tmp_ret = bx.load(addr, addr_align);
+        bx.load(tmp_ret, align.abi)
+    } else {
+        bx.load(addr, addr_align)
+    }
+}
+
+fn emit_aapcs_va_arg(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+) -> &'ll Value {
+    // Implementation of the AAPCS64 calling convention for va_args see
+    // https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst
+    let va_list_addr = list.immediate();
+    let layout = bx.cx.layout_of(target_ty);
+
+    let mut maybe_reg = bx.build_sibling_block("va_arg.maybe_reg");
+    let mut in_reg = bx.build_sibling_block("va_arg.in_reg");
+    let mut on_stack = bx.build_sibling_block("va_arg.on_stack");
+    let mut end = bx.build_sibling_block("va_arg.end");
+    let zero = bx.const_i32(0);
+    let offset_align = Align::from_bytes(4).unwrap();
+    assert!(&*bx.tcx().sess.target.target.target_endian == "little");
+
+    let gr_type = target_ty.is_any_ptr() || target_ty.is_integral();
+    let (reg_off, reg_top_index, slot_size) = if gr_type {
+        let gr_offs = bx.struct_gep(va_list_addr, 7);
+        let nreg = (layout.size.bytes() + 7) / 8;
+        (gr_offs, 3, nreg * 8)
+    } else {
+        let vr_off = bx.struct_gep(va_list_addr, 9);
+        let nreg = (layout.size.bytes() + 15) / 16;
+        (vr_off, 5, nreg * 16)
+    };
+
+    // if the offset >= 0 then the value will be on the stack
+    let mut reg_off_v = bx.load(reg_off, offset_align);
+    let use_stack = bx.icmp(IntPredicate::IntSGE, reg_off_v, zero);
+    bx.cond_br(use_stack, &on_stack.llbb(), &maybe_reg.llbb());
+
+    // The value at this point might be in a register, but there is a chance that
+    // it could be on the stack so we have to update the offset and then check
+    // the offset again.
+
+    if gr_type && layout.align.abi.bytes() > 8 {
+        reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(15));
+        reg_off_v = maybe_reg.and(reg_off_v, bx.const_i32(-16));
+    }
+    let new_reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(slot_size as i32));
+
+    maybe_reg.store(new_reg_off_v, reg_off, offset_align);
+
+    // Check to see if we have overflowed the registers as a result of this.
+    // If we have then we need to use the stack for this value
+    let use_stack = maybe_reg.icmp(IntPredicate::IntSGT, new_reg_off_v, zero);
+    maybe_reg.cond_br(use_stack, &on_stack.llbb(), &in_reg.llbb());
+
+    let top = in_reg.struct_gep(va_list_addr, reg_top_index);
+    let top = in_reg.load(top, bx.tcx().data_layout.pointer_align.abi);
+
+    // reg_value = *(@top + reg_off_v);
+    let top = in_reg.gep(top, &[reg_off_v]);
+    let top = in_reg.bitcast(top, bx.cx.type_ptr_to(layout.llvm_type(bx)));
+    let reg_value = in_reg.load(top, layout.align.abi);
+    in_reg.br(&end.llbb());
+
+    // On Stack block
+    let stack_value =
+        emit_ptr_va_arg(&mut on_stack, list, target_ty, false, Align::from_bytes(8).unwrap(), true);
+    on_stack.br(&end.llbb());
+
+    let val = end.phi(
+        layout.immediate_llvm_type(bx),
+        &[reg_value, stack_value],
+        &[&in_reg.llbb(), &on_stack.llbb()],
+    );
+
+    *bx = end;
+    val
+}
+
+pub(super) fn emit_va_arg(
+    bx: &mut Builder<'a, 'll, 'tcx>,
+    addr: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+) -> &'ll Value {
+    // Determine the va_arg implementation to use. The LLVM va_arg instruction
+    // is lacking in some instances, so we should only use it as a fallback.
+    let target = &bx.cx.tcx.sess.target.target;
+    let arch = &bx.cx.tcx.sess.target.target.arch;
+    match (&**arch, target.options.is_like_windows) {
+        // Windows x86
+        ("x86", true) => {
+            emit_ptr_va_arg(bx, addr, target_ty, false, Align::from_bytes(4).unwrap(), false)
+        }
+        // Generic x86
+        ("x86", _) => {
+            emit_ptr_va_arg(bx, addr, target_ty, false, Align::from_bytes(4).unwrap(), true)
+        }
+        // Windows AArch64
+        ("aarch64", true) => {
+            emit_ptr_va_arg(bx, addr, target_ty, false, Align::from_bytes(8).unwrap(), false)
+        }
+        // iOS AArch64
+        ("aarch64", _) if target.target_os == "ios" => {
+            emit_ptr_va_arg(bx, addr, target_ty, false, Align::from_bytes(8).unwrap(), true)
+        }
+        ("aarch64", _) => emit_aapcs_va_arg(bx, addr, target_ty),
+        // Windows x86_64
+        ("x86_64", true) => {
+            let target_ty_size = bx.cx.size_of(target_ty).bytes();
+            let indirect: bool = target_ty_size > 8 || !target_ty_size.is_power_of_two();
+            emit_ptr_va_arg(bx, addr, target_ty, indirect, Align::from_bytes(8).unwrap(), false)
+        }
+        // For all other architecture/OS combinations fall back to using
+        // the LLVM va_arg instruction.
+        // https://llvm.org/docs/LangRef.html#va-arg-instruction
+        _ => bx.va_arg(addr.immediate(), bx.cx.layout_of(target_ty).llvm_type(bx.cx)),
+    }
+}