compiler/rustc_target/src/callconv/riscv.rs - rust-lang/rust - Git at Google

 // Reference: RISC-V ELF psABI specification
 // https://github.com/riscv/riscv-elf-psabi-doc
 //
 // Reference: Clang RISC-V ELF psABI lowering code
 // https://github.com/llvm/llvm-project/blob/8e780252a7284be45cf1ba224cabd884847e8e92/clang/lib/CodeGen/TargetInfo.cpp#L9311-L9773

 use rustc_abi::{
     BackendRepr, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size, TyAbiInterface,
     TyAndLayout, Variants,
 };

 use crate::callconv::{ArgAbi, ArgExtension, CastTarget, FnAbi, PassMode, Uniform};
 use crate::spec::HasTargetSpec;

 #[derive(Copy, Clone)]
 enum RegPassKind {
     Float { offset_from_start: Size, ty: Reg },
     Integer { offset_from_start: Size, ty: Reg },
     Unknown,
 }

 #[derive(Copy, Clone)]
 enum FloatConv {
     FloatPair { first_ty: Reg, second_ty_offset_from_start: Size, second_ty: Reg },
     Float(Reg),
     MixedPair { first_ty: Reg, second_ty_offset_from_start: Size, second_ty: Reg },
 }

 #[derive(Copy, Clone)]
 struct CannotUseFpConv;

 fn is_riscv_aggregate<Ty>(arg: &ArgAbi<'_, Ty>) -> bool {
     match arg.layout.backend_repr {
         BackendRepr::SimdVector { .. } => true,
         _ => arg.layout.is_aggregate(),
     }
 }

 fn should_use_fp_conv_helper<'a, Ty, C>(
     cx: &C,
     arg_layout: &TyAndLayout<'a, Ty>,
     xlen: u64,
     flen: u64,
     field1_kind: &mut RegPassKind,
     field2_kind: &mut RegPassKind,
     offset_from_start: Size,
 ) -> Result<(), CannotUseFpConv>
 where
     Ty: TyAbiInterface<'a, C> + Copy,
 {
     match arg_layout.backend_repr {
         BackendRepr::Scalar(scalar) => match scalar.primitive() {
             Primitive::Int(..) | Primitive::Pointer(_) => {
                 if arg_layout.size.bits() > xlen {
                     return Err(CannotUseFpConv);
                 }
                 match (*field1_kind, *field2_kind) {
                     (RegPassKind::Unknown, _) => {
                         *field1_kind = RegPassKind::Integer {
                             offset_from_start,
                             ty: Reg { kind: RegKind::Integer, size: arg_layout.size },
                         };
                     }
                     (RegPassKind::Float { .. }, RegPassKind::Unknown) => {
                         *field2_kind = RegPassKind::Integer {
                             offset_from_start,
                             ty: Reg { kind: RegKind::Integer, size: arg_layout.size },
                         };
                     }
                     _ => return Err(CannotUseFpConv),
                 }
             }
             Primitive::Float(_) => {
                 if arg_layout.size.bits() > flen {
                     return Err(CannotUseFpConv);
                 }
                 match (*field1_kind, *field2_kind) {
                     (RegPassKind::Unknown, _) => {
                         *field1_kind = RegPassKind::Float {
                             offset_from_start,
                             ty: Reg { kind: RegKind::Float, size: arg_layout.size },
                         };
                     }
                     (_, RegPassKind::Unknown) => {
                         *field2_kind = RegPassKind::Float {
                             offset_from_start,
                             ty: Reg { kind: RegKind::Float, size: arg_layout.size },
                         };
                     }
                     _ => return Err(CannotUseFpConv),
                 }
             }
         },
         BackendRepr::SimdVector { .. } => return Err(CannotUseFpConv),
         BackendRepr::ScalarPair(..) | BackendRepr::Memory { .. } => match arg_layout.fields {
             FieldsShape::Primitive => {
                 unreachable!("aggregates can't have `FieldsShape::Primitive`")
             }
             FieldsShape::Union(_) => {
                 if !arg_layout.is_zst() {
                     if arg_layout.is_transparent() {
                         let non_1zst_elem = arg_layout.non_1zst_field(cx).expect("not exactly one non-1-ZST field in non-ZST repr(transparent) union").1;
                         return should_use_fp_conv_helper(
                             cx,
                             &non_1zst_elem,
                             xlen,
                             flen,
                             field1_kind,
                             field2_kind,
                             offset_from_start,
                         );
                     }
                     return Err(CannotUseFpConv);
                 }
             }
             FieldsShape::Array { count, .. } => {
                 for i in 0..count {
                     let elem_layout = arg_layout.field(cx, 0);
                     should_use_fp_conv_helper(
                         cx,
                         &elem_layout,
                         xlen,
                         flen,
                         field1_kind,
                         field2_kind,
                         offset_from_start + elem_layout.size * i,
                     )?;
                 }
             }
             FieldsShape::Arbitrary { .. } => {
                 match arg_layout.variants {
                     Variants::Multiple { .. } => return Err(CannotUseFpConv),
                     Variants::Single { .. } | Variants::Empty => (),
                 }
                 for i in arg_layout.fields.index_by_increasing_offset() {
                     let field = arg_layout.field(cx, i);
                     should_use_fp_conv_helper(
                         cx,
                         &field,
                         xlen,
                         flen,
                         field1_kind,
                         field2_kind,
                         offset_from_start + arg_layout.fields.offset(i),
                     )?;
                 }
             }
         },
     }
     Ok(())
 }

 fn should_use_fp_conv<'a, Ty, C>(
     cx: &C,
     arg: &TyAndLayout<'a, Ty>,
     xlen: u64,
     flen: u64,
 ) -> Option<FloatConv>
 where
     Ty: TyAbiInterface<'a, C> + Copy,
 {
     let mut field1_kind = RegPassKind::Unknown;
     let mut field2_kind = RegPassKind::Unknown;
     if should_use_fp_conv_helper(
         cx,
         arg,
         xlen,
         flen,
         &mut field1_kind,
         &mut field2_kind,
         Size::ZERO,
     )
     .is_err()
     {
         return None;
     }
     match (field1_kind, field2_kind) {
         (
             RegPassKind::Integer { offset_from_start, .. }
             | RegPassKind::Float { offset_from_start, .. },
             _,
         ) if offset_from_start != Size::ZERO => {
             panic!("type {:?} has a first field with non-zero offset {offset_from_start:?}", arg.ty)
         }
         (
             RegPassKind::Integer { ty: first_ty, .. },
             RegPassKind::Float { offset_from_start, ty: second_ty },
         ) => Some(FloatConv::MixedPair {
             first_ty,
             second_ty_offset_from_start: offset_from_start,
             second_ty,
         }),
         (
             RegPassKind::Float { ty: first_ty, .. },
             RegPassKind::Integer { offset_from_start, ty: second_ty },
         ) => Some(FloatConv::MixedPair {
             first_ty,
             second_ty_offset_from_start: offset_from_start,
             second_ty,
         }),
         (
             RegPassKind::Float { ty: first_ty, .. },
             RegPassKind::Float { offset_from_start, ty: second_ty },
         ) => Some(FloatConv::FloatPair {
             first_ty,
             second_ty_offset_from_start: offset_from_start,
             second_ty,
         }),
         (RegPassKind::Float { ty, .. }, RegPassKind::Unknown) => Some(FloatConv::Float(ty)),
         _ => None,
     }
 }

 fn classify_ret<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, xlen: u64, flen: u64) -> bool
 where
     Ty: TyAbiInterface<'a, C> + Copy,
 {
     if !arg.layout.is_sized() {
         // Not touching this...
         return false; // I guess? return value of this function is not documented
     }
     if let Some(conv) = should_use_fp_conv(cx, &arg.layout, xlen, flen) {
         match conv {
             FloatConv::Float(f) => {
                 arg.cast_to(f);
             }
             FloatConv::FloatPair { first_ty, second_ty_offset_from_start, second_ty } => {
                 arg.cast_to(CastTarget::offset_pair(
                     first_ty,
                     second_ty_offset_from_start,
                     second_ty,
                 ));
             }
             FloatConv::MixedPair { first_ty, second_ty_offset_from_start, second_ty } => {
                 arg.cast_to(CastTarget::offset_pair(
                     first_ty,
                     second_ty_offset_from_start,
                     second_ty,
                 ));
             }
         }
         return false;
     }

     let total = arg.layout.size;

     // "Scalars wider than 2✕XLEN are passed by reference and are replaced in
     // the argument list with the address."
     // "Aggregates larger than 2✕XLEN bits are passed by reference and are
     // replaced in the argument list with the address, as are C++ aggregates
     // with nontrivial copy constructors, destructors, or vtables."
     if total.bits() > 2 * xlen {
         // We rely on the LLVM backend lowering code to lower passing a scalar larger than 2*XLEN.
         if is_riscv_aggregate(arg) {
             arg.make_indirect();
         }
         return true;
     }

     let xlen_reg = match xlen {
         32 => Reg::i32(),
         64 => Reg::i64(),
         _ => unreachable!("Unsupported XLEN: {}", xlen),
     };
     if is_riscv_aggregate(arg) {
         if total.bits() <= xlen {
             arg.cast_to(xlen_reg);
         } else {
             arg.cast_to(Uniform::new(xlen_reg, Size::from_bits(xlen * 2)));
         }
         return false;
     }

     // "When passed in registers, scalars narrower than XLEN bits are widened
     // according to the sign of their type up to 32 bits, then sign-extended to
     // XLEN bits."
     extend_integer_width(arg, xlen);
     false
 }

 fn classify_arg<'a, Ty, C>(
     cx: &C,
     arg: &mut ArgAbi<'a, Ty>,
     xlen: u64,
     flen: u64,
     is_vararg: bool,
     avail_gprs: &mut u64,
     avail_fprs: &mut u64,
 ) where
     Ty: TyAbiInterface<'a, C> + Copy,
 {
     if !arg.layout.is_sized() {
         // Not touching this...
         return;
     }
     if !is_vararg {
         match should_use_fp_conv(cx, &arg.layout, xlen, flen) {
             Some(FloatConv::Float(f)) if *avail_fprs >= 1 => {
                 *avail_fprs -= 1;
                 arg.cast_to(f);
                 return;
             }
             Some(FloatConv::FloatPair { first_ty, second_ty_offset_from_start, second_ty })
                 if *avail_fprs >= 2 =>
             {
                 *avail_fprs -= 2;
                 arg.cast_to(CastTarget::offset_pair(
                     first_ty,
                     second_ty_offset_from_start,
                     second_ty,
                 ));
                 return;
             }
             Some(FloatConv::MixedPair { first_ty, second_ty_offset_from_start, second_ty })
                 if *avail_fprs >= 1 && *avail_gprs >= 1 =>
             {
                 *avail_gprs -= 1;
                 *avail_fprs -= 1;
                 arg.cast_to(CastTarget::offset_pair(
                     first_ty,
                     second_ty_offset_from_start,
                     second_ty,
                 ));
                 return;
             }
             _ => (),
         }
     }

     let total = arg.layout.size;
     let align = arg.layout.align.abi.bits();

     // "Scalars wider than 2✕XLEN are passed by reference and are replaced in
     // the argument list with the address."
     // "Aggregates larger than 2✕XLEN bits are passed by reference and are
     // replaced in the argument list with the address, as are C++ aggregates
     // with nontrivial copy constructors, destructors, or vtables."
     if total.bits() > 2 * xlen {
         // We rely on the LLVM backend lowering code to lower passing a scalar larger than 2*XLEN.
         if is_riscv_aggregate(arg) {
             arg.make_indirect();
         }
         if *avail_gprs >= 1 {
             *avail_gprs -= 1;
         }
         return;
     }

     let double_xlen_reg = match xlen {
         32 => Reg::i64(),
         64 => Reg::i128(),
         _ => unreachable!("Unsupported XLEN: {}", xlen),
     };

     let xlen_reg = match xlen {
         32 => Reg::i32(),
         64 => Reg::i64(),
         _ => unreachable!("Unsupported XLEN: {}", xlen),
     };

     if total.bits() > xlen {
         let align_regs = align > xlen;
         if is_riscv_aggregate(arg) {
             arg.cast_to(Uniform::new(
                 if align_regs { double_xlen_reg } else { xlen_reg },
                 Size::from_bits(xlen * 2),
             ));
         }
         if align_regs && is_vararg {
             *avail_gprs -= *avail_gprs % 2;
         }
         if *avail_gprs >= 2 {
             *avail_gprs -= 2;
         } else {
             *avail_gprs = 0;
         }
         return;
     } else if is_riscv_aggregate(arg) {
         arg.cast_to(xlen_reg);
         if *avail_gprs >= 1 {
             *avail_gprs -= 1;
         }
         return;
     }

     // "When passed in registers, scalars narrower than XLEN bits are widened
     // according to the sign of their type up to 32 bits, then sign-extended to
     // XLEN bits."
     if *avail_gprs >= 1 {
         extend_integer_width(arg, xlen);
         *avail_gprs -= 1;
     }
 }

 fn extend_integer_width<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64) {
     if let BackendRepr::Scalar(scalar) = arg.layout.backend_repr
         && let Primitive::Int(i, _) = scalar.primitive()
         && i.size().bits() == 32
         && xlen > 32
         && let PassMode::Direct(ref mut attrs) = arg.mode
     {
         attrs.ext(ArgExtension::Sext);
         return;
     }

     arg.extend_integer_width_to(xlen);
 }

 pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
     let flen = match &cx.target_spec().llvm_abiname[..] {
         "ilp32f" | "lp64f" => 32,
         "ilp32d" | "lp64d" => 64,
         _ => 0,
     };
     let xlen = cx.data_layout().pointer_size().bits();

     let mut avail_gprs = 8;
     let mut avail_fprs = 8;

     if !fn_abi.ret.is_ignore() && classify_ret(cx, &mut fn_abi.ret, xlen, flen) {
         avail_gprs -= 1;
     }

     for (i, arg) in fn_abi.args.iter_mut().enumerate() {
         if arg.is_ignore() {
             continue;
         }
         classify_arg(
             cx,
             arg,
             xlen,
             flen,
             i >= fn_abi.fixed_count as usize,
             &mut avail_gprs,
             &mut avail_fprs,
         );
     }
 }

 pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout + HasTargetSpec,
 {
     let xlen = cx.data_layout().pointer_size().bits();

     for arg in fn_abi.args.iter_mut() {
         if arg.is_ignore() {
             continue;
         }

         // LLVM integers types do not differentiate between signed or unsigned integers.
         // Some RISC-V instructions do not have a `.w` suffix version, they use all the
         // XLEN bits. By explicitly setting the `signext` or `zeroext` attribute
         // according to signedness to avoid unnecessary integer extending instructions.
         //
         // See https://github.com/rust-lang/rust/issues/114508 for details.
         extend_integer_width(arg, xlen);
     }
 }
	// Reference: RISC-V ELF psABI specification
	// https://github.com/riscv/riscv-elf-psabi-doc
	//
	// Reference: Clang RISC-V ELF psABI lowering code
	// https://github.com/llvm/llvm-project/blob/8e780252a7284be45cf1ba224cabd884847e8e92/clang/lib/CodeGen/TargetInfo.cpp#L9311-L9773

	use rustc_abi::{
	BackendRepr, FieldsShape, HasDataLayout, Primitive, Reg, RegKind, Size, TyAbiInterface,
	TyAndLayout, Variants,
	};

	use crate::callconv::{ArgAbi, ArgExtension, CastTarget, FnAbi, PassMode, Uniform};
	use crate::spec::HasTargetSpec;

	#[derive(Copy, Clone)]
	enum RegPassKind {
	Float { offset_from_start: Size, ty: Reg },
	Integer { offset_from_start: Size, ty: Reg },
	Unknown,
	}

	#[derive(Copy, Clone)]
	enum FloatConv {
	FloatPair { first_ty: Reg, second_ty_offset_from_start: Size, second_ty: Reg },
	Float(Reg),
	MixedPair { first_ty: Reg, second_ty_offset_from_start: Size, second_ty: Reg },
	}

	#[derive(Copy, Clone)]
	struct CannotUseFpConv;

	fn is_riscv_aggregate<Ty>(arg: &ArgAbi<'_, Ty>) -> bool {
	match arg.layout.backend_repr {
	BackendRepr::SimdVector { .. } => true,
	_ => arg.layout.is_aggregate(),
	}
	}

	fn should_use_fp_conv_helper<'a, Ty, C>(
	cx: &C,
	arg_layout: &TyAndLayout<'a, Ty>,
	xlen: u64,
	flen: u64,
	field1_kind: &mut RegPassKind,
	field2_kind: &mut RegPassKind,
	offset_from_start: Size,
	) -> Result<(), CannotUseFpConv>
	where
	Ty: TyAbiInterface<'a, C> + Copy,
	{
	match arg_layout.backend_repr {
	BackendRepr::Scalar(scalar) => match scalar.primitive() {
	Primitive::Int(..) \| Primitive::Pointer(_) => {
	if arg_layout.size.bits() > xlen {
	return Err(CannotUseFpConv);
	}
	match (field1_kind, field2_kind) {
	(RegPassKind::Unknown, _) => {
	*field1_kind = RegPassKind::Integer {
	offset_from_start,
	ty: Reg { kind: RegKind::Integer, size: arg_layout.size },
	};
	}
	(RegPassKind::Float { .. }, RegPassKind::Unknown) => {
	*field2_kind = RegPassKind::Integer {
	offset_from_start,
	ty: Reg { kind: RegKind::Integer, size: arg_layout.size },
	};
	}
	_ => return Err(CannotUseFpConv),
	}
	}
	Primitive::Float(_) => {
	if arg_layout.size.bits() > flen {
	return Err(CannotUseFpConv);
	}
	match (field1_kind, field2_kind) {
	(RegPassKind::Unknown, _) => {
	*field1_kind = RegPassKind::Float {
	offset_from_start,
	ty: Reg { kind: RegKind::Float, size: arg_layout.size },
	};
	}
	(_, RegPassKind::Unknown) => {
	*field2_kind = RegPassKind::Float {
	offset_from_start,
	ty: Reg { kind: RegKind::Float, size: arg_layout.size },
	};
	}
	_ => return Err(CannotUseFpConv),
	}
	}
	},
	BackendRepr::SimdVector { .. } => return Err(CannotUseFpConv),
	BackendRepr::ScalarPair(..) \| BackendRepr::Memory { .. } => match arg_layout.fields {
	FieldsShape::Primitive => {
	unreachable!("aggregates can't have `FieldsShape::Primitive`")
	}
	FieldsShape::Union(_) => {
	if !arg_layout.is_zst() {
	if arg_layout.is_transparent() {
	let non_1zst_elem = arg_layout.non_1zst_field(cx).expect("not exactly one non-1-ZST field in non-ZST repr(transparent) union").1;
	return should_use_fp_conv_helper(
	cx,
	&non_1zst_elem,
	xlen,
	flen,
	field1_kind,
	field2_kind,
	offset_from_start,
	);
	}
	return Err(CannotUseFpConv);
	}
	}
	FieldsShape::Array { count, .. } => {
	for i in 0..count {
	let elem_layout = arg_layout.field(cx, 0);
	should_use_fp_conv_helper(
	cx,
	&elem_layout,
	xlen,
	flen,
	field1_kind,
	field2_kind,
	offset_from_start + elem_layout.size * i,
	)?;
	}
	}
	FieldsShape::Arbitrary { .. } => {
	match arg_layout.variants {
	Variants::Multiple { .. } => return Err(CannotUseFpConv),
	Variants::Single { .. } \| Variants::Empty => (),
	}
	for i in arg_layout.fields.index_by_increasing_offset() {
	let field = arg_layout.field(cx, i);
	should_use_fp_conv_helper(
	cx,
	&field,
	xlen,
	flen,
	field1_kind,
	field2_kind,
	offset_from_start + arg_layout.fields.offset(i),
	)?;
	}
	}
	},
	}
	Ok(())
	}

	fn should_use_fp_conv<'a, Ty, C>(
	cx: &C,
	arg: &TyAndLayout<'a, Ty>,
	xlen: u64,
	flen: u64,
	) -> Option<FloatConv>
	where
	Ty: TyAbiInterface<'a, C> + Copy,
	{
	let mut field1_kind = RegPassKind::Unknown;
	let mut field2_kind = RegPassKind::Unknown;
	if should_use_fp_conv_helper(
	cx,
	arg,
	xlen,
	flen,
	&mut field1_kind,
	&mut field2_kind,
	Size::ZERO,
	)
	.is_err()
	{
	return None;
	}
	match (field1_kind, field2_kind) {
	(
	RegPassKind::Integer { offset_from_start, .. }
	\| RegPassKind::Float { offset_from_start, .. },
	_,
	) if offset_from_start != Size::ZERO => {
	panic!("type {:?} has a first field with non-zero offset {offset_from_start:?}", arg.ty)
	}
	(
	RegPassKind::Integer { ty: first_ty, .. },
	RegPassKind::Float { offset_from_start, ty: second_ty },
	) => Some(FloatConv::MixedPair {
	first_ty,
	second_ty_offset_from_start: offset_from_start,
	second_ty,
	}),
	(
	RegPassKind::Float { ty: first_ty, .. },
	RegPassKind::Integer { offset_from_start, ty: second_ty },
	) => Some(FloatConv::MixedPair {
	first_ty,
	second_ty_offset_from_start: offset_from_start,
	second_ty,
	}),
	(
	RegPassKind::Float { ty: first_ty, .. },
	RegPassKind::Float { offset_from_start, ty: second_ty },
	) => Some(FloatConv::FloatPair {
	first_ty,
	second_ty_offset_from_start: offset_from_start,
	second_ty,
	}),
	(RegPassKind::Float { ty, .. }, RegPassKind::Unknown) => Some(FloatConv::Float(ty)),
	_ => None,
	}
	}

	fn classify_ret<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, xlen: u64, flen: u64) -> bool
	where
	Ty: TyAbiInterface<'a, C> + Copy,
	{
	if !arg.layout.is_sized() {
	// Not touching this...
	return false; // I guess? return value of this function is not documented
	}
	if let Some(conv) = should_use_fp_conv(cx, &arg.layout, xlen, flen) {
	match conv {
	FloatConv::Float(f) => {
	arg.cast_to(f);
	}
	FloatConv::FloatPair { first_ty, second_ty_offset_from_start, second_ty } => {
	arg.cast_to(CastTarget::offset_pair(
	first_ty,
	second_ty_offset_from_start,
	second_ty,
	));
	}
	FloatConv::MixedPair { first_ty, second_ty_offset_from_start, second_ty } => {
	arg.cast_to(CastTarget::offset_pair(
	first_ty,
	second_ty_offset_from_start,
	second_ty,
	));
	}
	}
	return false;
	}

	let total = arg.layout.size;

	// "Scalars wider than 2✕XLEN are passed by reference and are replaced in
	// the argument list with the address."
	// "Aggregates larger than 2✕XLEN bits are passed by reference and are
	// replaced in the argument list with the address, as are C++ aggregates
	// with nontrivial copy constructors, destructors, or vtables."
	if total.bits() > 2 * xlen {
	// We rely on the LLVM backend lowering code to lower passing a scalar larger than 2*XLEN.
	if is_riscv_aggregate(arg) {
	arg.make_indirect();
	}
	return true;
	}

	let xlen_reg = match xlen {
	32 => Reg::i32(),
	64 => Reg::i64(),
	_ => unreachable!("Unsupported XLEN: {}", xlen),
	};
	if is_riscv_aggregate(arg) {
	if total.bits() <= xlen {
	arg.cast_to(xlen_reg);
	} else {
	arg.cast_to(Uniform::new(xlen_reg, Size::from_bits(xlen * 2)));
	}
	return false;
	}

	// "When passed in registers, scalars narrower than XLEN bits are widened
	// according to the sign of their type up to 32 bits, then sign-extended to
	// XLEN bits."
	extend_integer_width(arg, xlen);
	false
	}

	fn classify_arg<'a, Ty, C>(
	cx: &C,
	arg: &mut ArgAbi<'a, Ty>,
	xlen: u64,
	flen: u64,
	is_vararg: bool,
	avail_gprs: &mut u64,
	avail_fprs: &mut u64,
	) where
	Ty: TyAbiInterface<'a, C> + Copy,
	{
	if !arg.layout.is_sized() {
	// Not touching this...
	return;
	}
	if !is_vararg {
	match should_use_fp_conv(cx, &arg.layout, xlen, flen) {
	Some(FloatConv::Float(f)) if *avail_fprs >= 1 => {
	*avail_fprs -= 1;
	arg.cast_to(f);
	return;
	}
	Some(FloatConv::FloatPair { first_ty, second_ty_offset_from_start, second_ty })
	if *avail_fprs >= 2 =>
	{
	*avail_fprs -= 2;
	arg.cast_to(CastTarget::offset_pair(
	first_ty,
	second_ty_offset_from_start,
	second_ty,
	));
	return;
	}
	Some(FloatConv::MixedPair { first_ty, second_ty_offset_from_start, second_ty })
	if avail_fprs >= 1 && avail_gprs >= 1 =>
	{
	*avail_gprs -= 1;
	*avail_fprs -= 1;
	arg.cast_to(CastTarget::offset_pair(
	first_ty,
	second_ty_offset_from_start,
	second_ty,
	));
	return;
	}
	_ => (),
	}
	}

	let total = arg.layout.size;
	let align = arg.layout.align.abi.bits();

	// "Scalars wider than 2✕XLEN are passed by reference and are replaced in
	// the argument list with the address."
	// "Aggregates larger than 2✕XLEN bits are passed by reference and are
	// replaced in the argument list with the address, as are C++ aggregates
	// with nontrivial copy constructors, destructors, or vtables."
	if total.bits() > 2 * xlen {
	// We rely on the LLVM backend lowering code to lower passing a scalar larger than 2*XLEN.
	if is_riscv_aggregate(arg) {
	arg.make_indirect();
	}
	if *avail_gprs >= 1 {
	*avail_gprs -= 1;
	}
	return;
	}

	let double_xlen_reg = match xlen {
	32 => Reg::i64(),
	64 => Reg::i128(),
	_ => unreachable!("Unsupported XLEN: {}", xlen),
	};

	let xlen_reg = match xlen {
	32 => Reg::i32(),
	64 => Reg::i64(),
	_ => unreachable!("Unsupported XLEN: {}", xlen),
	};

	if total.bits() > xlen {
	let align_regs = align > xlen;
	if is_riscv_aggregate(arg) {
	arg.cast_to(Uniform::new(
	if align_regs { double_xlen_reg } else { xlen_reg },
	Size::from_bits(xlen * 2),
	));
	}
	if align_regs && is_vararg {
	avail_gprs -= avail_gprs % 2;
	}
	if *avail_gprs >= 2 {
	*avail_gprs -= 2;
	} else {
	*avail_gprs = 0;
	}
	return;
	} else if is_riscv_aggregate(arg) {
	arg.cast_to(xlen_reg);
	if *avail_gprs >= 1 {
	*avail_gprs -= 1;
	}
	return;
	}

	// "When passed in registers, scalars narrower than XLEN bits are widened
	// according to the sign of their type up to 32 bits, then sign-extended to
	// XLEN bits."
	if *avail_gprs >= 1 {
	extend_integer_width(arg, xlen);
	*avail_gprs -= 1;
	}
	}

	fn extend_integer_width<Ty>(arg: &mut ArgAbi<'_, Ty>, xlen: u64) {
	if let BackendRepr::Scalar(scalar) = arg.layout.backend_repr
	&& let Primitive::Int(i, _) = scalar.primitive()
	&& i.size().bits() == 32
	&& xlen > 32
	&& let PassMode::Direct(ref mut attrs) = arg.mode
	{
	attrs.ext(ArgExtension::Sext);
	return;
	}

	arg.extend_integer_width_to(xlen);
	}

	pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
	where
	Ty: TyAbiInterface<'a, C> + Copy,
	C: HasDataLayout + HasTargetSpec,
	{
	let flen = match &cx.target_spec().llvm_abiname[..] {
	"ilp32f" \| "lp64f" => 32,
	"ilp32d" \| "lp64d" => 64,
	_ => 0,
	};
	let xlen = cx.data_layout().pointer_size().bits();

	let mut avail_gprs = 8;
	let mut avail_fprs = 8;

	if !fn_abi.ret.is_ignore() && classify_ret(cx, &mut fn_abi.ret, xlen, flen) {
	avail_gprs -= 1;
	}

	for (i, arg) in fn_abi.args.iter_mut().enumerate() {
	if arg.is_ignore() {
	continue;
	}
	classify_arg(
	cx,
	arg,
	xlen,
	flen,
	i >= fn_abi.fixed_count as usize,
	&mut avail_gprs,
	&mut avail_fprs,
	);
	}
	}

	pub(crate) fn compute_rust_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
	where
	Ty: TyAbiInterface<'a, C> + Copy,
	C: HasDataLayout + HasTargetSpec,
	{
	let xlen = cx.data_layout().pointer_size().bits();

	for arg in fn_abi.args.iter_mut() {
	if arg.is_ignore() {
	continue;
	}

	// LLVM integers types do not differentiate between signed or unsigned integers.
	// Some RISC-V instructions do not have a `.w` suffix version, they use all the
	// XLEN bits. By explicitly setting the `signext` or `zeroext` attribute
	// according to signedness to avoid unnecessary integer extending instructions.
	//
	// See https://github.com/rust-lang/rust/issues/114508 for details.
	extend_integer_width(arg, xlen);
	}
	}