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Fix LoongArch C function ABI when passing/returning structs containing floats #145709

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Sep 5, 2025
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Fix LoongArch C function ABI when passing/returning structs containing floats #145709

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137 changes: 105 additions & 32 deletions compiler/rustc_target/src/callconv/loongarch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,16 +8,16 @@ use crate::spec::HasTargetSpec;

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

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

#[derive(Copy, Clone)]
Expand All @@ -37,6 +37,7 @@ fn should_use_fp_conv_helper<'a, Ty, C>(
flen: u64,
field1_kind: &mut RegPassKind,
field2_kind: &mut RegPassKind,
offset_from_start: Size,
) -> Result<(), CannotUseFpConv>
where
Ty: TyAbiInterface<'a, C> + Copy,
Expand All @@ -49,16 +50,16 @@ where
}
match (*field1_kind, *field2_kind) {
(RegPassKind::Unknown, _) => {
*field1_kind = RegPassKind::Integer(Reg {
kind: RegKind::Integer,
size: arg_layout.size,
});
*field1_kind = RegPassKind::Integer {
offset_from_start,
ty: Reg { kind: RegKind::Integer, size: arg_layout.size },
};
}
(RegPassKind::Float(_), RegPassKind::Unknown) => {
*field2_kind = RegPassKind::Integer(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),
}
Expand All @@ -69,12 +70,16 @@ where
}
match (*field1_kind, *field2_kind) {
(RegPassKind::Unknown, _) => {
*field1_kind =
RegPassKind::Float(Reg { kind: RegKind::Float, size: arg_layout.size });
*field1_kind = RegPassKind::Float {
offset_from_start,
ty: Reg { kind: RegKind::Float, size: arg_layout.size },
};
}
(_, RegPassKind::Unknown) => {
*field2_kind =
RegPassKind::Float(Reg { kind: RegKind::Float, size: arg_layout.size });
*field2_kind = RegPassKind::Float {
offset_from_start,
ty: Reg { kind: RegKind::Float, size: arg_layout.size },
};
}
_ => return Err(CannotUseFpConv),
}
Expand All @@ -96,13 +101,14 @@ where
flen,
field1_kind,
field2_kind,
offset_from_start,
);
}
return Err(CannotUseFpConv);
}
}
FieldsShape::Array { count, .. } => {
for _ in 0..count {
for i in 0..count {
let elem_layout = arg_layout.field(cx, 0);
should_use_fp_conv_helper(
cx,
Expand All @@ -111,6 +117,7 @@ where
flen,
field1_kind,
field2_kind,
offset_from_start + elem_layout.size * i,
)?;
}
}
Expand All @@ -121,7 +128,15 @@ where
}
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)?;
should_use_fp_conv_helper(
cx,
&field,
xlen,
flen,
field1_kind,
field2_kind,
offset_from_start + arg_layout.fields.offset(i),
)?;
}
}
},
Expand All @@ -140,14 +155,52 @@ where
{
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).is_err() {
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(l), RegPassKind::Float(r)) => Some(FloatConv::MixedPair(l, r)),
(RegPassKind::Float(l), RegPassKind::Integer(r)) => Some(FloatConv::MixedPair(l, r)),
(RegPassKind::Float(l), RegPassKind::Float(r)) => Some(FloatConv::FloatPair(l, r)),
(RegPassKind::Float(f), RegPassKind::Unknown) => Some(FloatConv::Float(f)),
(
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,
}
}
Expand All @@ -165,11 +218,19 @@ where
FloatConv::Float(f) => {
arg.cast_to(f);
}
FloatConv::FloatPair(l, r) => {
arg.cast_to(CastTarget::pair(l, r));
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(l, r) => {
arg.cast_to(CastTarget::pair(l, r));
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;
Expand Down Expand Up @@ -233,15 +294,27 @@ fn classify_arg<'a, Ty, C>(
arg.cast_to(f);
return;
}
Some(FloatConv::FloatPair(l, r)) if *avail_fprs >= 2 => {
Some(FloatConv::FloatPair { first_ty, second_ty_offset_from_start, second_ty })
if *avail_fprs >= 2 =>
{
*avail_fprs -= 2;
arg.cast_to(CastTarget::pair(l, r));
arg.cast_to(CastTarget::offset_pair(
first_ty,
second_ty_offset_from_start,
second_ty,
));
return;
}
Some(FloatConv::MixedPair(l, r)) if *avail_fprs >= 1 && *avail_gprs >= 1 => {
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::pair(l, r));
arg.cast_to(CastTarget::offset_pair(
first_ty,
second_ty_offset_from_start,
second_ty,
));
return;
}
_ => (),
Expand Down
134 changes: 134 additions & 0 deletions tests/assembly-llvm/loongarch-float-struct-abi.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,134 @@
//@ add-core-stubs
//@ assembly-output: emit-asm
//@ compile-flags: -Copt-level=3 --target loongarch64-unknown-linux-gnu
//@ needs-llvm-components: loongarch

#![feature(no_core, lang_items)]
#![no_std]
#![no_core]
#![crate_type = "lib"]

extern crate minicore;
use minicore::*;

#[repr(C, align(64))]
struct Aligned(f64);

#[repr(C)]
struct Padded(u8, Aligned);

#[repr(C, packed)]
struct Packed(u8, f32);

impl Copy for Aligned {}
impl Copy for Padded {}
impl Copy for Packed {}

extern "C" {
fn take_padded(x: Padded);
fn get_padded() -> Padded;
fn take_packed(x: Packed);
fn get_packed() -> Packed;
}

// CHECK-LABEL: pass_padded
#[unsafe(no_mangle)]
extern "C" fn pass_padded(out: &mut Padded, x: Padded) {
// CHECK: st.b $a1, $a0, 0
// CHECK-NEXT: fst.d $fa0, $a0, 64
// CHECK-NEXT: ret
*out = x;
}

// CHECK-LABEL: ret_padded
#[unsafe(no_mangle)]
extern "C" fn ret_padded(x: &Padded) -> Padded {
// CHECK: fld.d $fa0, $a0, 64
// CHECK-NEXT: ld.b $a0, $a0, 0
// CHECK-NEXT: ret
*x
}

#[unsafe(no_mangle)]
extern "C" fn call_padded(x: &Padded) {
// CHECK: fld.d $fa0, $a0, 64
// CHECK-NEXT: ld.b $a0, $a0, 0
// CHECK-NEXT: pcaddu18i $t8, %call36(take_padded)
// CHECK-NEXT: jr $t8
unsafe {
take_padded(*x);
}
}

#[unsafe(no_mangle)]
extern "C" fn receive_padded(out: &mut Padded) {
// CHECK: addi.d $sp, $sp, -16
// CHECK-NEXT: .cfi_def_cfa_offset 16
// CHECK-NEXT: st.d $ra, $sp, [[#%d,RA_SPILL:]]
// CHECK-NEXT: st.d [[TEMP:.*]], $sp, [[#%d,TEMP_SPILL:]]
// CHECK-NEXT: .cfi_offset 1, [[#%d,RA_SPILL - 16]]
// CHECK-NEXT: .cfi_offset [[#%d,TEMP_NUM:]], [[#%d,TEMP_SPILL - 16]]
// CHECK-NEXT: move [[TEMP]], $a0
// CHECK-NEXT: pcaddu18i $ra, %call36(get_padded)
// CHECK-NEXT: jirl $ra, $ra, 0
// CHECK-NEXT: st.b $a0, [[TEMP]], 0
// CHECK-NEXT: fst.d $fa0, [[TEMP]], 64
// CHECK-NEXT: ld.d [[TEMP]], $sp, [[#%d,TEMP_SPILL]]
// CHECK-NEXT: ld.d $ra, $sp, [[#%d,RA_SPILL]]
// CHECK: addi.d $sp, $sp, 16
// CHECK: ret
unsafe {
*out = get_padded();
}
}

// CHECK-LABEL: pass_packed
#[unsafe(no_mangle)]
extern "C" fn pass_packed(out: &mut Packed, x: Packed) {
// CHECK: st.b $a1, $a0, 0
// CHECK-NEXT: fst.s $fa0, $a0, 1
// CHECK-NEXT: ret
*out = x;
}

// CHECK-LABEL: ret_packed
#[unsafe(no_mangle)]
extern "C" fn ret_packed(x: &Packed) -> Packed {
// CHECK: fld.s $fa0, $a0, 1
// CHECK-NEXT: ld.b $a0, $a0, 0
// CHECK-NEXT: ret
*x
}

#[unsafe(no_mangle)]
extern "C" fn call_packed(x: &Packed) {
// CHECK: fld.s $fa0, $a0, 1
// CHECK-NEXT: ld.b $a0, $a0, 0
// CHECK-NEXT: pcaddu18i $t8, %call36(take_packed)
// CHECK-NEXT: jr $t8
unsafe {
take_packed(*x);
}
}

#[unsafe(no_mangle)]
extern "C" fn receive_packed(out: &mut Packed) {
// CHECK: addi.d $sp, $sp, -16
// CHECK-NEXT: .cfi_def_cfa_offset 16
// CHECK-NEXT: st.d $ra, $sp, [[#%d,RA_SPILL:]]
// CHECK-NEXT: st.d [[TEMP:.*]], $sp, [[#%d,TEMP_SPILL:]]
// CHECK-NEXT: .cfi_offset 1, [[#%d,RA_SPILL - 16]]
// CHECK-NEXT: .cfi_offset [[#%d,TEMP_NUM:]], [[#%d,TEMP_SPILL - 16]]
// CHECK-NEXT: move [[TEMP]], $a0
// CHECK-NEXT: pcaddu18i $ra, %call36(get_packed)
// CHECK-NEXT: jirl $ra, $ra, 0
// CHECK-NEXT: st.b $a0, [[TEMP]], 0
// CHECK-NEXT: fst.s $fa0, [[TEMP]], 1
// CHECK-NEXT: ld.d [[TEMP]], $sp, [[#%d,TEMP_SPILL]]
// CHECK-NEXT: ld.d $ra, $sp, [[#%d,RA_SPILL]]
// CHECK: addi.d $sp, $sp, 16
// CHECK: ret
unsafe {
*out = get_packed();
}
}
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