Auto merge of #18317 - lnicola:sync-from-rust, r=Veykril

minor: sync from downstream

4 files changed, 532 insertions, 1 deletions

diff --git a/compiler/rustc_abi/src/callconv.rs b/compiler/rustc_abi/src/callconv.rs
new file mode 100644
index 00000000000..2ecac8a9df1
--- /dev/null
+++ b/compiler/rustc_abi/src/callconv.rs
@@ -0,0 +1,254 @@
+mod abi {
+    pub(crate) use crate::Primitive::*;
+    pub(crate) use crate::Variants;
+}
+
+use rustc_macros::HashStable_Generic;
+
+use crate::{Abi, Align, FieldsShape, HasDataLayout, Size, TyAbiInterface, TyAndLayout};
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
+pub enum RegKind {
+    Integer,
+    Float,
+    Vector,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
+pub struct Reg {
+    pub kind: RegKind,
+    pub size: Size,
+}
+
+macro_rules! reg_ctor {
+    ($name:ident, $kind:ident, $bits:expr) => {
+        pub fn $name() -> Reg {
+            Reg { kind: RegKind::$kind, size: Size::from_bits($bits) }
+        }
+    };
+}
+
+impl Reg {
+    reg_ctor!(i8, Integer, 8);
+    reg_ctor!(i16, Integer, 16);
+    reg_ctor!(i32, Integer, 32);
+    reg_ctor!(i64, Integer, 64);
+    reg_ctor!(i128, Integer, 128);
+
+    reg_ctor!(f32, Float, 32);
+    reg_ctor!(f64, Float, 64);
+}
+
+impl Reg {
+    pub fn align<C: HasDataLayout>(&self, cx: &C) -> Align {
+        let dl = cx.data_layout();
+        match self.kind {
+            RegKind::Integer => match self.size.bits() {
+                1 => dl.i1_align.abi,
+                2..=8 => dl.i8_align.abi,
+                9..=16 => dl.i16_align.abi,
+                17..=32 => dl.i32_align.abi,
+                33..=64 => dl.i64_align.abi,
+                65..=128 => dl.i128_align.abi,
+                _ => panic!("unsupported integer: {self:?}"),
+            },
+            RegKind::Float => match self.size.bits() {
+                16 => dl.f16_align.abi,
+                32 => dl.f32_align.abi,
+                64 => dl.f64_align.abi,
+                128 => dl.f128_align.abi,
+                _ => panic!("unsupported float: {self:?}"),
+            },
+            RegKind::Vector => dl.vector_align(self.size).abi,
+        }
+    }
+}
+
+/// Return value from the `homogeneous_aggregate` test function.
+#[derive(Copy, Clone, Debug)]
+pub enum HomogeneousAggregate {
+    /// Yes, all the "leaf fields" of this struct are passed in the
+    /// same way (specified in the `Reg` value).
+    Homogeneous(Reg),
+
+    /// There are no leaf fields at all.
+    NoData,
+}
+
+/// Error from the `homogeneous_aggregate` test function, indicating
+/// there are distinct leaf fields passed in different ways,
+/// or this is uninhabited.
+#[derive(Copy, Clone, Debug)]
+pub struct Heterogeneous;
+
+impl HomogeneousAggregate {
+    /// If this is a homogeneous aggregate, returns the homogeneous
+    /// unit, else `None`.
+    pub fn unit(self) -> Option<Reg> {
+        match self {
+            HomogeneousAggregate::Homogeneous(reg) => Some(reg),
+            HomogeneousAggregate::NoData => None,
+        }
+    }
+
+    /// Try to combine two `HomogeneousAggregate`s, e.g. from two fields in
+    /// the same `struct`. Only succeeds if only one of them has any data,
+    /// or both units are identical.
+    fn merge(self, other: HomogeneousAggregate) -> Result<HomogeneousAggregate, Heterogeneous> {
+        match (self, other) {
+            (x, HomogeneousAggregate::NoData) | (HomogeneousAggregate::NoData, x) => Ok(x),
+
+            (HomogeneousAggregate::Homogeneous(a), HomogeneousAggregate::Homogeneous(b)) => {
+                if a != b {
+                    return Err(Heterogeneous);
+                }
+                Ok(self)
+            }
+        }
+    }
+}
+
+impl<'a, Ty> TyAndLayout<'a, Ty> {
+    /// Returns `true` if this is an aggregate type (including a ScalarPair!)
+    pub fn is_aggregate(&self) -> bool {
+        match self.abi {
+            Abi::Uninhabited | Abi::Scalar(_) | Abi::Vector { .. } => false,
+            Abi::ScalarPair(..) | Abi::Aggregate { .. } => true,
+        }
+    }
+
+    /// Returns `Homogeneous` if this layout is an aggregate containing fields of
+    /// only a single type (e.g., `(u32, u32)`). Such aggregates are often
+    /// special-cased in ABIs.
+    ///
+    /// Note: We generally ignore 1-ZST fields when computing this value (see #56877).
+    ///
+    /// This is public so that it can be used in unit tests, but
+    /// should generally only be relevant to the ABI details of
+    /// specific targets.
+    pub fn homogeneous_aggregate<C>(&self, cx: &C) -> Result<HomogeneousAggregate, Heterogeneous>
+    where
+        Ty: TyAbiInterface<'a, C> + Copy,
+    {
+        match self.abi {
+            Abi::Uninhabited => Err(Heterogeneous),
+
+            // The primitive for this algorithm.
+            Abi::Scalar(scalar) => {
+                let kind = match scalar.primitive() {
+                    abi::Int(..) | abi::Pointer(_) => RegKind::Integer,
+                    abi::Float(_) => RegKind::Float,
+                };
+                Ok(HomogeneousAggregate::Homogeneous(Reg { kind, size: self.size }))
+            }
+
+            Abi::Vector { .. } => {
+                assert!(!self.is_zst());
+                Ok(HomogeneousAggregate::Homogeneous(Reg {
+                    kind: RegKind::Vector,
+                    size: self.size,
+                }))
+            }
+
+            Abi::ScalarPair(..) | Abi::Aggregate { sized: true } => {
+                // Helper for computing `homogeneous_aggregate`, allowing a custom
+                // starting offset (used below for handling variants).
+                let from_fields_at =
+                    |layout: Self,
+                     start: Size|
+                     -> Result<(HomogeneousAggregate, Size), Heterogeneous> {
+                        let is_union = match layout.fields {
+                            FieldsShape::Primitive => {
+                                unreachable!("aggregates can't have `FieldsShape::Primitive`")
+                            }
+                            FieldsShape::Array { count, .. } => {
+                                assert_eq!(start, Size::ZERO);
+
+                                let result = if count > 0 {
+                                    layout.field(cx, 0).homogeneous_aggregate(cx)?
+                                } else {
+                                    HomogeneousAggregate::NoData
+                                };
+                                return Ok((result, layout.size));
+                            }
+                            FieldsShape::Union(_) => true,
+                            FieldsShape::Arbitrary { .. } => false,
+                        };
+
+                        let mut result = HomogeneousAggregate::NoData;
+                        let mut total = start;
+
+                        for i in 0..layout.fields.count() {
+                            let field = layout.field(cx, i);
+                            if field.is_1zst() {
+                                // No data here and no impact on layout, can be ignored.
+                                // (We might be able to also ignore all aligned ZST but that's less clear.)
+                                continue;
+                            }
+
+                            if !is_union && total != layout.fields.offset(i) {
+                                // This field isn't just after the previous one we considered, abort.
+                                return Err(Heterogeneous);
+                            }
+
+                            result = result.merge(field.homogeneous_aggregate(cx)?)?;
+
+                            // Keep track of the offset (without padding).
+                            let size = field.size;
+                            if is_union {
+                                total = total.max(size);
+                            } else {
+                                total += size;
+                            }
+                        }
+
+                        Ok((result, total))
+                    };
+
+                let (mut result, mut total) = from_fields_at(*self, Size::ZERO)?;
+
+                match &self.variants {
+                    abi::Variants::Single { .. } => {}
+                    abi::Variants::Multiple { variants, .. } => {
+                        // Treat enum variants like union members.
+                        // HACK(eddyb) pretend the `enum` field (discriminant)
+                        // is at the start of every variant (otherwise the gap
+                        // at the start of all variants would disqualify them).
+                        //
+                        // NB: for all tagged `enum`s (which include all non-C-like
+                        // `enum`s with defined FFI representation), this will
+                        // match the homogeneous computation on the equivalent
+                        // `struct { tag; union { variant1; ... } }` and/or
+                        // `union { struct { tag; variant1; } ... }`
+                        // (the offsets of variant fields should be identical
+                        // between the two for either to be a homogeneous aggregate).
+                        let variant_start = total;
+                        for variant_idx in variants.indices() {
+                            let (variant_result, variant_total) =
+                                from_fields_at(self.for_variant(cx, variant_idx), variant_start)?;
+
+                            result = result.merge(variant_result)?;
+                            total = total.max(variant_total);
+                        }
+                    }
+                }
+
+                // There needs to be no padding.
+                if total != self.size {
+                    Err(Heterogeneous)
+                } else {
+                    match result {
+                        HomogeneousAggregate::Homogeneous(_) => {
+                            assert_ne!(total, Size::ZERO);
+                        }
+                        HomogeneousAggregate::NoData => {
+                            assert_eq!(total, Size::ZERO);
+                        }
+                    }
+                    Ok(result)
+                }
+            }
+            Abi::Aggregate { sized: false } => Err(Heterogeneous),
+        }
+    }
+}
diff --git a/compiler/rustc_abi/src/layout.rs b/compiler/rustc_abi/src/layout.rs
index 620a051eeb7..6e1299944a0 100644
--- a/compiler/rustc_abi/src/layout.rs
+++ b/compiler/rustc_abi/src/layout.rs
@@ -11,6 +11,10 @@ use crate::{
     Variants, WrappingRange,
 };
 
+mod ty;
+
+pub use ty::{FIRST_VARIANT, FieldIdx, Layout, TyAbiInterface, TyAndLayout, VariantIdx};
+
 // A variant is absent if it's uninhabited and only has ZST fields.
 // Present uninhabited variants only require space for their fields,
 // but *not* an encoding of the discriminant (e.g., a tag value).
diff --git a/compiler/rustc_abi/src/layout/ty.rs b/compiler/rustc_abi/src/layout/ty.rs
new file mode 100644
index 00000000000..c6812c4d4c0
--- /dev/null
+++ b/compiler/rustc_abi/src/layout/ty.rs
@@ -0,0 +1,267 @@
+use std::fmt;
+use std::ops::Deref;
+
+use Float::*;
+use Primitive::*;
+use rustc_data_structures::intern::Interned;
+use rustc_macros::HashStable_Generic;
+
+// Explicitly import `Float` to avoid ambiguity with `Primitive::Float`.
+use crate::{Float, *};
+
+rustc_index::newtype_index! {
+    /// The *source-order* index of a field in a variant.
+    ///
+    /// This is how most code after type checking refers to fields, rather than
+    /// using names (as names have hygiene complications and more complex lookup).
+    ///
+    /// Particularly for `repr(Rust)` types, this may not be the same as *layout* order.
+    /// (It is for `repr(C)` `struct`s, however.)
+    ///
+    /// For example, in the following types,
+    /// ```rust
+    /// # enum Never {}
+    /// # #[repr(u16)]
+    /// enum Demo1 {
+    ///    Variant0 { a: Never, b: i32 } = 100,
+    ///    Variant1 { c: u8, d: u64 } = 10,
+    /// }
+    /// struct Demo2 { e: u8, f: u16, g: u8 }
+    /// ```
+    /// `b` is `FieldIdx(1)` in `VariantIdx(0)`,
+    /// `d` is `FieldIdx(1)` in `VariantIdx(1)`, and
+    /// `f` is `FieldIdx(1)` in `VariantIdx(0)`.
+    #[derive(HashStable_Generic)]
+    #[encodable]
+    #[orderable]
+    pub struct FieldIdx {}
+}
+
+rustc_index::newtype_index! {
+    /// The *source-order* index of a variant in a type.
+    ///
+    /// For enums, these are always `0..variant_count`, regardless of any
+    /// custom discriminants that may have been defined, and including any
+    /// variants that may end up uninhabited due to field types.  (Some of the
+    /// variants may not be present in a monomorphized ABI [`Variants`], but
+    /// those skipped variants are always counted when determining the *index*.)
+    ///
+    /// `struct`s, `tuples`, and `unions`s are considered to have a single variant
+    /// with variant index zero, aka [`FIRST_VARIANT`].
+    #[derive(HashStable_Generic)]
+    #[encodable]
+    #[orderable]
+    pub struct VariantIdx {
+        /// Equivalent to `VariantIdx(0)`.
+        const FIRST_VARIANT = 0;
+    }
+}
+#[derive(Copy, Clone, PartialEq, Eq, Hash, HashStable_Generic)]
+#[rustc_pass_by_value]
+pub struct Layout<'a>(pub Interned<'a, LayoutS<FieldIdx, VariantIdx>>);
+
+impl<'a> fmt::Debug for Layout<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // See comment on `<LayoutS as Debug>::fmt` above.
+        self.0.0.fmt(f)
+    }
+}
+
+impl<'a> Deref for Layout<'a> {
+    type Target = &'a LayoutS<FieldIdx, VariantIdx>;
+    fn deref(&self) -> &&'a LayoutS<FieldIdx, VariantIdx> {
+        &self.0.0
+    }
+}
+
+impl<'a> Layout<'a> {
+    pub fn fields(self) -> &'a FieldsShape<FieldIdx> {
+        &self.0.0.fields
+    }
+
+    pub fn variants(self) -> &'a Variants<FieldIdx, VariantIdx> {
+        &self.0.0.variants
+    }
+
+    pub fn abi(self) -> Abi {
+        self.0.0.abi
+    }
+
+    pub fn largest_niche(self) -> Option<Niche> {
+        self.0.0.largest_niche
+    }
+
+    pub fn align(self) -> AbiAndPrefAlign {
+        self.0.0.align
+    }
+
+    pub fn size(self) -> Size {
+        self.0.0.size
+    }
+
+    pub fn max_repr_align(self) -> Option<Align> {
+        self.0.0.max_repr_align
+    }
+
+    pub fn unadjusted_abi_align(self) -> Align {
+        self.0.0.unadjusted_abi_align
+    }
+
+    /// Whether the layout is from a type that implements [`std::marker::PointerLike`].
+    ///
+    /// Currently, that means that the type is pointer-sized, pointer-aligned,
+    /// and has a initialized (non-union), scalar ABI.
+    pub fn is_pointer_like(self, data_layout: &TargetDataLayout) -> bool {
+        self.size() == data_layout.pointer_size
+            && self.align().abi == data_layout.pointer_align.abi
+            && matches!(self.abi(), Abi::Scalar(Scalar::Initialized { .. }))
+    }
+}
+
+/// The layout of a type, alongside the type itself.
+/// Provides various type traversal APIs (e.g., recursing into fields).
+///
+/// Note that the layout is NOT guaranteed to always be identical
+/// to that obtained from `layout_of(ty)`, as we need to produce
+/// layouts for which Rust types do not exist, such as enum variants
+/// or synthetic fields of enums (i.e., discriminants) and wide pointers.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, HashStable_Generic)]
+pub struct TyAndLayout<'a, Ty> {
+    pub ty: Ty,
+    pub layout: Layout<'a>,
+}
+
+impl<'a, Ty: fmt::Display> fmt::Debug for TyAndLayout<'a, Ty> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Print the type in a readable way, not its debug representation.
+        f.debug_struct("TyAndLayout")
+            .field("ty", &format_args!("{}", self.ty))
+            .field("layout", &self.layout)
+            .finish()
+    }
+}
+
+impl<'a, Ty> Deref for TyAndLayout<'a, Ty> {
+    type Target = &'a LayoutS<FieldIdx, VariantIdx>;
+    fn deref(&self) -> &&'a LayoutS<FieldIdx, VariantIdx> {
+        &self.layout.0.0
+    }
+}
+
+/// Trait that needs to be implemented by the higher-level type representation
+/// (e.g. `rustc_middle::ty::Ty`), to provide `rustc_target::abi` functionality.
+pub trait TyAbiInterface<'a, C>: Sized + std::fmt::Debug {
+    fn ty_and_layout_for_variant(
+        this: TyAndLayout<'a, Self>,
+        cx: &C,
+        variant_index: VariantIdx,
+    ) -> TyAndLayout<'a, Self>;
+    fn ty_and_layout_field(this: TyAndLayout<'a, Self>, cx: &C, i: usize) -> TyAndLayout<'a, Self>;
+    fn ty_and_layout_pointee_info_at(
+        this: TyAndLayout<'a, Self>,
+        cx: &C,
+        offset: Size,
+    ) -> Option<PointeeInfo>;
+    fn is_adt(this: TyAndLayout<'a, Self>) -> bool;
+    fn is_never(this: TyAndLayout<'a, Self>) -> bool;
+    fn is_tuple(this: TyAndLayout<'a, Self>) -> bool;
+    fn is_unit(this: TyAndLayout<'a, Self>) -> bool;
+    fn is_transparent(this: TyAndLayout<'a, Self>) -> bool;
+}
+
+impl<'a, Ty> TyAndLayout<'a, Ty> {
+    pub fn for_variant<C>(self, cx: &C, variant_index: VariantIdx) -> Self
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::ty_and_layout_for_variant(self, cx, variant_index)
+    }
+
+    pub fn field<C>(self, cx: &C, i: usize) -> Self
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::ty_and_layout_field(self, cx, i)
+    }
+
+    pub fn pointee_info_at<C>(self, cx: &C, offset: Size) -> Option<PointeeInfo>
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::ty_and_layout_pointee_info_at(self, cx, offset)
+    }
+
+    pub fn is_single_fp_element<C>(self, cx: &C) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+        C: HasDataLayout,
+    {
+        match self.abi {
+            Abi::Scalar(scalar) => matches!(scalar.primitive(), Float(F32 | F64)),
+            Abi::Aggregate { .. } => {
+                if self.fields.count() == 1 && self.fields.offset(0).bytes() == 0 {
+                    self.field(cx, 0).is_single_fp_element(cx)
+                } else {
+                    false
+                }
+            }
+            _ => false,
+        }
+    }
+
+    pub fn is_adt<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_adt(self)
+    }
+
+    pub fn is_never<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_never(self)
+    }
+
+    pub fn is_tuple<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_tuple(self)
+    }
+
+    pub fn is_unit<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_unit(self)
+    }
+
+    pub fn is_transparent<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_transparent(self)
+    }
+
+    /// Finds the one field that is not a 1-ZST.
+    /// Returns `None` if there are multiple non-1-ZST fields or only 1-ZST-fields.
+    pub fn non_1zst_field<C>(&self, cx: &C) -> Option<(usize, Self)>
+    where
+        Ty: TyAbiInterface<'a, C> + Copy,
+    {
+        let mut found = None;
+        for field_idx in 0..self.fields.count() {
+            let field = self.field(cx, field_idx);
+            if field.is_1zst() {
+                continue;
+            }
+            if found.is_some() {
+                // More than one non-1-ZST field.
+                return None;
+            }
+            found = Some((field_idx, field));
+        }
+        found
+    }
+}
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
index fa7c98a7fa0..84d756b6d51 100644
--- a/compiler/rustc_abi/src/lib.rs
+++ b/compiler/rustc_abi/src/lib.rs
@@ -1,6 +1,7 @@
 // tidy-alphabetical-start
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 #![cfg_attr(feature = "nightly", doc(rust_logo))]
+#![cfg_attr(feature = "nightly", feature(rustc_attrs))]
 #![cfg_attr(feature = "nightly", feature(rustdoc_internals))]
 #![cfg_attr(feature = "nightly", feature(step_trait))]
 #![warn(unreachable_pub)]
@@ -22,11 +23,16 @@ use rustc_macros::HashStable_Generic;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_Generic, Encodable_Generic};
 
+mod callconv;
 mod layout;
 #[cfg(test)]
 mod tests;
 
-pub use layout::{LayoutCalculator, LayoutCalculatorError};
+pub use callconv::{Heterogeneous, HomogeneousAggregate, Reg, RegKind};
+pub use layout::{
+    FIRST_VARIANT, FieldIdx, Layout, LayoutCalculator, LayoutCalculatorError, TyAbiInterface,
+    TyAndLayout, VariantIdx,
+};
 
 /// Requirements for a `StableHashingContext` to be used in this crate.
 /// This is a hack to allow using the `HashStable_Generic` derive macro