Fix RISC-V C function ABI when passing/returning structs containing floats

10 files changed, 272 insertions, 134 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
index 9a0a5b51039..cd0afee0cfb 100644
--- a/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
+++ b/compiler/rustc_codegen_cranelift/src/abi/pass_mode.rs
@@ -40,7 +40,18 @@ fn apply_attrs_to_abi_param(param: AbiParam, arg_attrs: ArgAttributes) -> AbiPar
     }
 }
 
-fn cast_target_to_abi_params(cast: &CastTarget) -> SmallVec<[AbiParam; 2]> {
+fn cast_target_to_abi_params(cast: &CastTarget) -> SmallVec<[(Size, AbiParam); 2]> {
+    if let Some(offset_from_start) = cast.rest_offset {
+        assert!(cast.prefix[1..].iter().all(|p| p.is_none()));
+        assert_eq!(cast.rest.unit.size, cast.rest.total);
+        let first = cast.prefix[0].unwrap();
+        let second = cast.rest.unit;
+        return smallvec![
+            (Size::ZERO, reg_to_abi_param(first)),
+            (offset_from_start, reg_to_abi_param(second))
+        ];
+    }
+
     let (rest_count, rem_bytes) = if cast.rest.unit.size.bytes() == 0 {
         (0, 0)
     } else {
@@ -55,25 +66,32 @@ fn cast_target_to_abi_params(cast: &CastTarget) -> SmallVec<[AbiParam; 2]> {
     // different types in Cranelift IR. Instead a single array of primitive types is used.
 
     // Create list of fields in the main structure
-    let mut args = cast
+    let args = cast
         .prefix
         .iter()
         .flatten()
         .map(|&reg| reg_to_abi_param(reg))
-        .chain((0..rest_count).map(|_| reg_to_abi_param(cast.rest.unit)))
-        .collect::<SmallVec<_>>();
+        .chain((0..rest_count).map(|_| reg_to_abi_param(cast.rest.unit)));
+
+    let mut res = SmallVec::new();
+    let mut offset = Size::ZERO;
+
+    for arg in args {
+        res.push((offset, arg));
+        offset += Size::from_bytes(arg.value_type.bytes());
+    }
 
     // Append final integer
     if rem_bytes != 0 {
         // Only integers can be really split further.
         assert_eq!(cast.rest.unit.kind, RegKind::Integer);
-        args.push(reg_to_abi_param(Reg {
-            kind: RegKind::Integer,
-            size: Size::from_bytes(rem_bytes),
-        }));
+        res.push((
+            offset,
+            reg_to_abi_param(Reg { kind: RegKind::Integer, size: Size::from_bytes(rem_bytes) }),
+        ));
     }
 
-    args
+    res
 }
 
 impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
@@ -104,7 +122,7 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
             },
             PassMode::Cast { ref cast, pad_i32 } => {
                 assert!(!pad_i32, "padding support not yet implemented");
-                cast_target_to_abi_params(cast)
+                cast_target_to_abi_params(cast).into_iter().map(|(_, param)| param).collect()
             }
             PassMode::Indirect { attrs, meta_attrs: None, on_stack } => {
                 if on_stack {
@@ -160,9 +178,10 @@ impl<'tcx> ArgAbiExt<'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 }
                 _ => unreachable!("{:?}", self.layout.backend_repr),
             },
-            PassMode::Cast { ref cast, .. } => {
-                (None, cast_target_to_abi_params(cast).into_iter().collect())
-            }
+            PassMode::Cast { ref cast, .. } => (
+                None,
+                cast_target_to_abi_params(cast).into_iter().map(|(_, param)| param).collect(),
+            ),
             PassMode::Indirect { attrs, meta_attrs: None, on_stack } => {
                 assert!(!on_stack);
                 (
@@ -187,12 +206,14 @@ pub(super) fn to_casted_value<'tcx>(
 ) -> SmallVec<[Value; 2]> {
     let (ptr, meta) = arg.force_stack(fx);
     assert!(meta.is_none());
-    let mut offset = 0;
     cast_target_to_abi_params(cast)
         .into_iter()
-        .map(|param| {
-            let val = ptr.offset_i64(fx, offset).load(fx, param.value_type, MemFlags::new());
-            offset += i64::from(param.value_type.bytes());
+        .map(|(offset, param)| {
+            let val = ptr.offset_i64(fx, offset.bytes() as i64).load(
+                fx,
+                param.value_type,
+                MemFlags::new(),
+            );
             val
         })
         .collect()
@@ -205,7 +226,7 @@ pub(super) fn from_casted_value<'tcx>(
     cast: &CastTarget,
 ) -> CValue<'tcx> {
     let abi_params = cast_target_to_abi_params(cast);
-    let abi_param_size: u32 = abi_params.iter().map(|param| param.value_type.bytes()).sum();
+    let abi_param_size: u32 = abi_params.iter().map(|(_, param)| param.value_type.bytes()).sum();
     let layout_size = u32::try_from(layout.size.bytes()).unwrap();
     let ptr = fx.create_stack_slot(
         // Stack slot size may be bigger for example `[u8; 3]` which is packed into an `i32`.
@@ -214,16 +235,13 @@ pub(super) fn from_casted_value<'tcx>(
         std::cmp::max(abi_param_size, layout_size),
         u32::try_from(layout.align.abi.bytes()).unwrap(),
     );
-    let mut offset = 0;
     let mut block_params_iter = block_params.iter().copied();
-    for param in abi_params {
-        let val = ptr.offset_i64(fx, offset).store(
+    for (offset, _) in abi_params {
+        ptr.offset_i64(fx, offset.bytes() as i64).store(
             fx,
             block_params_iter.next().unwrap(),
             MemFlags::new(),
-        );
-        offset += i64::from(param.value_type.bytes());
-        val
+        )
     }
     assert_eq!(block_params_iter.next(), None, "Leftover block param");
     CValue::by_ref(ptr, layout)
diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
index 9e05b8f23aa..c921851b42b 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
@@ -626,7 +626,7 @@ impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 bx.lifetime_start(llscratch, scratch_size);
 
                 // ... where we first store the value...
-                bx.store(val, llscratch, scratch_align);
+                rustc_codegen_ssa::mir::store_cast(bx, cast, val, llscratch, scratch_align);
 
                 // ... and then memcpy it to the intended destination.
                 bx.memcpy(
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index aba63d75f1d..4b07c8aef91 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -229,7 +229,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 let llscratch = bx.alloca(scratch_size, scratch_align);
                 bx.lifetime_start(llscratch, scratch_size);
                 // ...store the value...
-                bx.store(val, llscratch, scratch_align);
+                rustc_codegen_ssa::mir::store_cast(bx, cast, val, llscratch, scratch_align);
                 // ... and then memcpy it to the intended destination.
                 bx.memcpy(
                     dst.val.llval,
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 43b87171d51..3df97429e09 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -1,6 +1,6 @@
 use std::cmp;
 
-use rustc_abi::{BackendRepr, ExternAbi, HasDataLayout, Reg, Size, WrappingRange};
+use rustc_abi::{Align, BackendRepr, ExternAbi, HasDataLayout, Reg, Size, WrappingRange};
 use rustc_ast as ast;
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_data_structures::packed::Pu128;
@@ -13,7 +13,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_session::config::OptLevel;
 use rustc_span::Span;
 use rustc_span::source_map::Spanned;
-use rustc_target::callconv::{ArgAbi, FnAbi, PassMode};
+use rustc_target::callconv::{ArgAbi, CastTarget, FnAbi, PassMode};
 use tracing::{debug, info};
 
 use super::operand::OperandRef;
@@ -558,8 +558,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     }
                     ZeroSized => bug!("ZST return value shouldn't be in PassMode::Cast"),
                 };
-                let ty = bx.cast_backend_type(cast_ty);
-                bx.load(ty, llslot, self.fn_abi.ret.layout.align.abi)
+                load_cast(bx, cast_ty, llslot, self.fn_abi.ret.layout.align.abi)
             }
         };
         bx.ret(llval);
@@ -1618,8 +1617,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     MemFlags::empty(),
                 );
                 // ...and then load it with the ABI type.
-                let cast_ty = bx.cast_backend_type(cast);
-                llval = bx.load(cast_ty, llscratch, scratch_align);
+                llval = load_cast(bx, cast, llscratch, scratch_align);
                 bx.lifetime_end(llscratch, scratch_size);
             } else {
                 // We can't use `PlaceRef::load` here because the argument
@@ -1969,3 +1967,47 @@ enum ReturnDest<'tcx, V> {
     /// Store a direct return value to an operand local place.
     DirectOperand(mir::Local),
 }
+
+fn load_cast<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    bx: &mut Bx,
+    cast: &CastTarget,
+    ptr: Bx::Value,
+    align: Align,
+) -> Bx::Value {
+    let cast_ty = bx.cast_backend_type(cast);
+    if let Some(offset_from_start) = cast.rest_offset {
+        assert!(cast.prefix[1..].iter().all(|p| p.is_none()));
+        assert_eq!(cast.rest.unit.size, cast.rest.total);
+        let first_ty = bx.reg_backend_type(&cast.prefix[0].unwrap());
+        let second_ty = bx.reg_backend_type(&cast.rest.unit);
+        let first = bx.load(first_ty, ptr, align);
+        let second_ptr = bx.inbounds_ptradd(ptr, bx.const_usize(offset_from_start.bytes()));
+        let second = bx.load(second_ty, second_ptr, align.restrict_for_offset(offset_from_start));
+        let res = bx.cx().const_poison(cast_ty);
+        let res = bx.insert_value(res, first, 0);
+        bx.insert_value(res, second, 1)
+    } else {
+        bx.load(cast_ty, ptr, align)
+    }
+}
+
+pub fn store_cast<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    bx: &mut Bx,
+    cast: &CastTarget,
+    value: Bx::Value,
+    ptr: Bx::Value,
+    align: Align,
+) {
+    if let Some(offset_from_start) = cast.rest_offset {
+        assert!(cast.prefix[1..].iter().all(|p| p.is_none()));
+        assert_eq!(cast.rest.unit.size, cast.rest.total);
+        assert!(cast.prefix[0].is_some());
+        let first = bx.extract_value(value, 0);
+        let second = bx.extract_value(value, 1);
+        bx.store(first, ptr, align);
+        let second_ptr = bx.inbounds_ptradd(ptr, bx.const_usize(offset_from_start.bytes()));
+        bx.store(second, second_ptr, align.restrict_for_offset(offset_from_start));
+    } else {
+        bx.store(value, ptr, align);
+    };
+}
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 96a04473aba..66c4af4c935 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -26,6 +26,7 @@ pub mod place;
 mod rvalue;
 mod statement;
 
+pub use self::block::store_cast;
 use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo};
 use self::operand::{OperandRef, OperandValue};
 use self::place::PlaceRef;
@@ -259,7 +260,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                     }
                     PassMode::Cast { ref cast, .. } => {
                         debug!("alloc: {:?} (return place) -> place", local);
-                        let size = cast.size(&start_bx);
+                        let size = cast.size(&start_bx).max(layout.size);
                         return LocalRef::Place(PlaceRef::alloca_size(&mut start_bx, size, layout));
                     }
                     _ => {}
diff --git a/compiler/rustc_target/src/callconv/mips64.rs b/compiler/rustc_target/src/callconv/mips64.rs
index 89f324bc313..77c0cf06fc1 100644
--- a/compiler/rustc_target/src/callconv/mips64.rs
+++ b/compiler/rustc_target/src/callconv/mips64.rs
@@ -2,9 +2,7 @@ use rustc_abi::{
     BackendRepr, FieldsShape, Float, HasDataLayout, Primitive, Reg, Size, TyAbiInterface,
 };
 
-use crate::callconv::{
-    ArgAbi, ArgAttribute, ArgAttributes, ArgExtension, CastTarget, FnAbi, PassMode, Uniform,
-};
+use crate::callconv::{ArgAbi, ArgExtension, CastTarget, FnAbi, PassMode, Uniform};
 
 fn extend_integer_width_mips<Ty>(arg: &mut ArgAbi<'_, Ty>, bits: u64) {
     // Always sign extend u32 values on 64-bit mips
@@ -140,16 +138,7 @@ where
 
     // Extract first 8 chunks as the prefix
     let rest_size = size - Size::from_bytes(8) * prefix_index as u64;
-    arg.cast_to(CastTarget {
-        prefix,
-        rest: Uniform::new(Reg::i64(), rest_size),
-        attrs: ArgAttributes {
-            regular: ArgAttribute::default(),
-            arg_ext: ArgExtension::None,
-            pointee_size: Size::ZERO,
-            pointee_align: None,
-        },
-    });
+    arg.cast_to(CastTarget::prefixed(prefix, Uniform::new(Reg::i64(), rest_size)));
 }
 
 pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
diff --git a/compiler/rustc_target/src/callconv/mod.rs b/compiler/rustc_target/src/callconv/mod.rs
index 2ff7a71ca82..71cc2a45563 100644
--- a/compiler/rustc_target/src/callconv/mod.rs
+++ b/compiler/rustc_target/src/callconv/mod.rs
@@ -197,6 +197,17 @@ impl ArgAttributes {
     }
 }
 
+impl From<ArgAttribute> for ArgAttributes {
+    fn from(value: ArgAttribute) -> Self {
+        Self {
+            regular: value,
+            arg_ext: ArgExtension::None,
+            pointee_size: Size::ZERO,
+            pointee_align: None,
+        }
+    }
+}
+
 /// An argument passed entirely registers with the
 /// same kind (e.g., HFA / HVA on PPC64 and AArch64).
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
@@ -251,6 +262,9 @@ impl Uniform {
 #[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 pub struct CastTarget {
     pub prefix: [Option<Reg>; 8],
+    /// The offset of `rest` from the start of the value. Currently only implemented for a `Reg`
+    /// pair created by the `offset_pair` method.
+    pub rest_offset: Option<Size>,
     pub rest: Uniform,
     pub attrs: ArgAttributes,
 }
@@ -263,42 +277,45 @@ impl From<Reg> for CastTarget {
 
 impl From<Uniform> for CastTarget {
     fn from(uniform: Uniform) -> CastTarget {
-        CastTarget {
-            prefix: [None; 8],
-            rest: uniform,
-            attrs: ArgAttributes {
-                regular: ArgAttribute::default(),
-                arg_ext: ArgExtension::None,
-                pointee_size: Size::ZERO,
-                pointee_align: None,
-            },
-        }
+        Self::prefixed([None; 8], uniform)
     }
 }
 
 impl CastTarget {
-    pub fn pair(a: Reg, b: Reg) -> CastTarget {
-        CastTarget {
+    pub fn prefixed(prefix: [Option<Reg>; 8], rest: Uniform) -> Self {
+        Self { prefix, rest_offset: None, rest, attrs: ArgAttributes::new() }
+    }
+
+    pub fn offset_pair(a: Reg, offset_from_start: Size, b: Reg) -> Self {
+        Self {
             prefix: [Some(a), None, None, None, None, None, None, None],
-            rest: Uniform::from(b),
-            attrs: ArgAttributes {
-                regular: ArgAttribute::default(),
-                arg_ext: ArgExtension::None,
-                pointee_size: Size::ZERO,
-                pointee_align: None,
-            },
+            rest_offset: Some(offset_from_start),
+            rest: b.into(),
+            attrs: ArgAttributes::new(),
         }
     }
 
+    pub fn with_attrs(mut self, attrs: ArgAttributes) -> Self {
+        self.attrs = attrs;
+        self
+    }
+
+    pub fn pair(a: Reg, b: Reg) -> CastTarget {
+        Self::prefixed([Some(a), None, None, None, None, None, None, None], Uniform::from(b))
+    }
+
     /// When you only access the range containing valid data, you can use this unaligned size;
     /// otherwise, use the safer `size` method.
     pub fn unaligned_size<C: HasDataLayout>(&self, _cx: &C) -> Size {
         // Prefix arguments are passed in specific designated registers
-        let prefix_size = self
-            .prefix
-            .iter()
-            .filter_map(|x| x.map(|reg| reg.size))
-            .fold(Size::ZERO, |acc, size| acc + size);
+        let prefix_size = if let Some(offset_from_start) = self.rest_offset {
+            offset_from_start
+        } else {
+            self.prefix
+                .iter()
+                .filter_map(|x| x.map(|reg| reg.size))
+                .fold(Size::ZERO, |acc, size| acc + size)
+        };
         // Remaining arguments are passed in chunks of the unit size
         let rest_size =
             self.rest.unit.size * self.rest.total.bytes().div_ceil(self.rest.unit.size.bytes());
@@ -322,9 +339,22 @@ impl CastTarget {
     /// Checks if these two `CastTarget` are equal enough to be considered "the same for all
     /// function call ABIs".
     pub fn eq_abi(&self, other: &Self) -> bool {
-        let CastTarget { prefix: prefix_l, rest: rest_l, attrs: attrs_l } = self;
-        let CastTarget { prefix: prefix_r, rest: rest_r, attrs: attrs_r } = other;
-        prefix_l == prefix_r && rest_l == rest_r && attrs_l.eq_abi(attrs_r)
+        let CastTarget {
+            prefix: prefix_l,
+            rest_offset: rest_offset_l,
+            rest: rest_l,
+            attrs: attrs_l,
+        } = self;
+        let CastTarget {
+            prefix: prefix_r,
+            rest_offset: rest_offset_r,
+            rest: rest_r,
+            attrs: attrs_r,
+        } = other;
+        prefix_l == prefix_r
+            && rest_offset_l == rest_offset_r
+            && rest_l == rest_r
+            && attrs_l.eq_abi(attrs_r)
     }
 }
 
diff --git a/compiler/rustc_target/src/callconv/nvptx64.rs b/compiler/rustc_target/src/callconv/nvptx64.rs
index a26e7dac5ba..44977de7fcb 100644
--- a/compiler/rustc_target/src/callconv/nvptx64.rs
+++ b/compiler/rustc_target/src/callconv/nvptx64.rs
@@ -1,6 +1,6 @@
 use rustc_abi::{HasDataLayout, Reg, Size, TyAbiInterface};
 
-use super::{ArgAttribute, ArgAttributes, ArgExtension, CastTarget};
+use super::CastTarget;
 use crate::callconv::{ArgAbi, FnAbi, Uniform};
 
 fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
@@ -34,16 +34,10 @@ fn classify_aggregate<Ty>(arg: &mut ArgAbi<'_, Ty>) {
     };
 
     if align_bytes == size.bytes() {
-        arg.cast_to(CastTarget {
-            prefix: [Some(reg), None, None, None, None, None, None, None],
-            rest: Uniform::new(Reg::i8(), Size::from_bytes(0)),
-            attrs: ArgAttributes {
-                regular: ArgAttribute::default(),
-                arg_ext: ArgExtension::None,
-                pointee_size: Size::ZERO,
-                pointee_align: None,
-            },
-        });
+        arg.cast_to(CastTarget::prefixed(
+            [Some(reg), None, None, None, None, None, None, None],
+            Uniform::new(Reg::i8(), Size::ZERO),
+        ));
     } else {
         arg.cast_to(Uniform::new(reg, size));
     }
@@ -78,11 +72,10 @@ where
     };
     if arg.layout.size.bytes() / align_bytes == 1 {
         // Make sure we pass the struct as array at the LLVM IR level and not as a single integer.
-        arg.cast_to(CastTarget {
-            prefix: [Some(unit), None, None, None, None, None, None, None],
-            rest: Uniform::new(unit, Size::ZERO),
-            attrs: ArgAttributes::new(),
-        });
+        arg.cast_to(CastTarget::prefixed(
+            [Some(unit), None, None, None, None, None, None, None],
+            Uniform::new(unit, Size::ZERO),
+        ));
     } else {
         arg.cast_to(Uniform::new(unit, arg.layout.size));
     }
diff --git a/compiler/rustc_target/src/callconv/riscv.rs b/compiler/rustc_target/src/callconv/riscv.rs
index cd1d3cd1eee..6a2038f9381 100644
--- a/compiler/rustc_target/src/callconv/riscv.rs
+++ b/compiler/rustc_target/src/callconv/riscv.rs
@@ -14,16 +14,16 @@ 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)]
@@ -43,6 +43,7 @@ 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,
@@ -55,16 +56,16 @@ 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),
                 }
@@ -75,12 +76,16 @@ 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),
                 }
@@ -102,13 +107,14 @@ 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,
@@ -117,6 +123,7 @@ where
                         flen,
                         field1_kind,
                         field2_kind,
+                        offset_from_start + elem_layout.size * i,
                     )?;
                 }
             }
@@ -127,7 +134,15 @@ 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),
+                    )?;
                 }
             }
         },
@@ -146,14 +161,52 @@ 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,
     }
 }
@@ -171,11 +224,19 @@ 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;
@@ -239,15 +300,27 @@ 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;
             }
             _ => (),
diff --git a/compiler/rustc_target/src/callconv/sparc64.rs b/compiler/rustc_target/src/callconv/sparc64.rs
index 7ca0031fc59..186826c08fc 100644
--- a/compiler/rustc_target/src/callconv/sparc64.rs
+++ b/compiler/rustc_target/src/callconv/sparc64.rs
@@ -5,9 +5,7 @@ use rustc_abi::{
     TyAndLayout,
 };
 
-use crate::callconv::{
-    ArgAbi, ArgAttribute, ArgAttributes, ArgExtension, CastTarget, FnAbi, Uniform,
-};
+use crate::callconv::{ArgAbi, ArgAttribute, CastTarget, FnAbi, Uniform};
 use crate::spec::HasTargetSpec;
 
 #[derive(Clone, Debug)]
@@ -197,16 +195,10 @@ where
                     rest_size = rest_size - Reg::i32().size;
                 }
 
-                arg.cast_to(CastTarget {
-                    prefix: data.prefix,
-                    rest: Uniform::new(Reg::i64(), rest_size),
-                    attrs: ArgAttributes {
-                        regular: data.arg_attribute,
-                        arg_ext: ArgExtension::None,
-                        pointee_size: Size::ZERO,
-                        pointee_align: None,
-                    },
-                });
+                arg.cast_to(
+                    CastTarget::prefixed(data.prefix, Uniform::new(Reg::i64(), rest_size))
+                        .with_attrs(data.arg_attribute.into()),
+                );
                 return;
             }
         }