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Box in ValTreeKind::Branch(Box<[I::Const]>) changed to List #152593

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Merged
rust-bors merged 4 commits into from
Mar 6, 2026
Merged

Box in ValTreeKind::Branch(Box<[I::Const]>) changed to List #152593

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0f786b9
ValTreeKind::Branch use List
spirali Feb 13, 2026
46ddd48
Changes after code review
spirali Feb 15, 2026
14b3a40
Test updated
spirali Feb 23, 2026
f8998e9
as_slice removed
spirali Mar 5, 2026
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2 changes: 2 additions & 0 deletions compiler/rustc_middle/src/ty/codec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ use std::marker::{DiscriminantKind, PointeeSized};
use rustc_abi::FieldIdx;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def_id::LocalDefId;
use rustc_middle::ty::Const;
use rustc_serialize::{Decodable, Encodable};
use rustc_span::source_map::Spanned;
use rustc_span::{Span, SpanDecoder, SpanEncoder};
Expand Down Expand Up @@ -498,6 +499,7 @@ impl_decodable_via_ref! {
&'tcx ty::List<ty::BoundVariableKind<'tcx>>,
&'tcx ty::List<ty::Pattern<'tcx>>,
&'tcx ty::ListWithCachedTypeInfo<ty::Clause<'tcx>>,
&'tcx ty::List<Const<'tcx>>,
}

#[macro_export]
Expand Down
6 changes: 4 additions & 2 deletions compiler/rustc_middle/src/ty/consts/valtree.rs
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Expand Up @@ -44,7 +44,7 @@ impl<'tcx> ValTree<'tcx> {
}

pub fn is_zst(self) -> bool {
matches!(*self, ty::ValTreeKind::Branch(box []))
matches!(*self, ty::ValTreeKind::Branch(consts) if consts.is_empty())
}

pub fn from_raw_bytes(tcx: TyCtxt<'tcx>, bytes: &[u8]) -> Self {
Expand All @@ -58,7 +58,9 @@ impl<'tcx> ValTree<'tcx> {
tcx: TyCtxt<'tcx>,
branches: impl IntoIterator<Item = ty::Const<'tcx>>,
) -> Self {
tcx.intern_valtree(ty::ValTreeKind::Branch(branches.into_iter().collect()))
tcx.intern_valtree(ty::ValTreeKind::Branch(
tcx.mk_const_list_from_iter(branches.into_iter()),
))
}

pub fn from_scalar_int(tcx: TyCtxt<'tcx>, i: ScalarInt) -> Self {
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/context.rs
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Expand Up @@ -565,7 +565,7 @@ impl<'tcx> CommonConsts<'tcx> {
))
};

let valtree_zst = mk_valtree(ty::ValTreeKind::Branch(Box::default()));
let valtree_zst = mk_valtree(ty::ValTreeKind::Branch(List::empty()));
let valtree_true = mk_valtree(ty::ValTreeKind::Leaf(ty::ScalarInt::TRUE));
let valtree_false = mk_valtree(ty::ValTreeKind::Leaf(ty::ScalarInt::FALSE));

Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/ty/context/impl_interner.rs
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Expand Up @@ -95,6 +95,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
type Safety = hir::Safety;
type Abi = ExternAbi;
type Const = ty::Const<'tcx>;
type Consts = &'tcx List<Self::Const>;

type ParamConst = ty::ParamConst;
type ValueConst = ty::Value<'tcx>;
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/print/pretty.rs
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Expand Up @@ -1920,7 +1920,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
}
// Otherwise, print the array separated by commas (or if it's a tuple)
(ty::ValTreeKind::Branch(fields), ty::Array(..) | ty::Tuple(..)) => {
let fields_iter = fields.iter().copied();

@lcnr lcnr Feb 14, 2026

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Consts should implement SliceLike so we can just do .iter() here now

@spirali spirali Feb 15, 2026

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Consts implements SliceLike, but .iter() on fields returns &Const and the following code works only for iterator over Const:

error[E0277]: the trait bound `&ty::consts::Const<'_>: print::Print<'tcx, Self>` is not satisfied
    --> compiler/rustc_middle/src/ty/print/pretty.rs:1964:34
     |
1964 | ...                   self.comma_sep(fields)?;
     |                            ^^^^^^^^^ the nightly-only, unstable trait `print::Print<'tcx, Self>` is not implemented for `&ty::consts::Const<'_>`
     |
help: the trait `Print<'tcx, _>` is not implemented for `&ty::consts::Const<'_>`
      but trait `Print<'_, _>` is implemented for `ty::consts::Const<'_>

@lcnr lcnr Feb 22, 2026

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I do think the as_slice should not be needed 🤔

Though given that we're in rustc_middle i guess this is the inherent impl for List or via deref?

@lcnr lcnr Feb 25, 2026

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still relevant, can you try removing the as_slice?

@lcnr lcnr Mar 5, 2026 •
edited
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^ (get rid of as_slice)

@spirali spirali Mar 5, 2026

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Ah, sorry, I have overlooked your original reply. It is fixed now.

let fields_iter = fields.as_slice().iter().copied();

match *cv.ty.kind() {
ty::Array(..) => {
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/ty/structural_impls.rs
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Expand Up @@ -805,4 +805,5 @@ list_fold! {
&'tcx ty::List<PlaceElem<'tcx>> : mk_place_elems,
&'tcx ty::List<ty::Pattern<'tcx>> : mk_patterns,
&'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>> : mk_outlives,
&'tcx ty::List<ty::Const<'tcx>> : mk_const_list,
}
6 changes: 4 additions & 2 deletions compiler/rustc_mir_build/src/builder/matches/mod.rs
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Expand Up @@ -2941,10 +2941,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {

match pat.ctor() {
Constructor::Variant(variant_index) => {
let ValTreeKind::Branch(box [actual_variant_idx]) = *valtree else {
let ValTreeKind::Branch(branch) = *valtree else {
bug!("malformed valtree for an enum")
};
let Some(actual_variant_idx) = branch.get(0) else {

@lcnr lcnr Feb 14, 2026

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we stop asserting that the len is 1 here

bug!("malformed valtree for an enum")
};

let ValTreeKind::Leaf(actual_variant_idx) = *actual_variant_idx.to_value().valtree
else {
bug!("malformed valtree for an enum")
Expand Down
8 changes: 4 additions & 4 deletions compiler/rustc_type_ir/src/const_kind.rs
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Expand Up @@ -9,6 +9,7 @@ use rustc_type_ir_macros::{
GenericTypeVisitable, Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic,
};

use crate::inherent::*;
use crate::{self as ty, BoundVarIndexKind, Interner};

/// Represents a constant in Rust.
Expand Down Expand Up @@ -159,8 +160,7 @@ pub enum ValTreeKind<I: Interner> {
/// the fields of the variant.
///
/// ZST types are represented as an empty slice.
// FIXME(mgca): Use a `List` here instead of a boxed slice
Branch(Box<[I::Const]>),
Branch(I::Consts),
}

impl<I: Interner> ValTreeKind<I> {
Expand All @@ -179,7 +179,7 @@ impl<I: Interner> ValTreeKind<I> {
#[inline]
pub fn to_branch(&self) -> &[I::Const] {

@lcnr lcnr Feb 14, 2026

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Suggested change
pub fn to_branch(&self) -> &[I::Const] {
pub fn to_branch(&self) -> I::Consts {

match self {
ValTreeKind::Branch(branch) => &**branch,
ValTreeKind::Branch(branch) => branch.as_slice(),
ValTreeKind::Leaf(..) => panic!("expected branch, got {:?}", self),
}
}
Expand All @@ -195,7 +195,7 @@ impl<I: Interner> ValTreeKind<I> {
/// Attempts to convert to a `ValTreeKind::Branch` value.
pub fn try_to_branch(&self) -> Option<&[I::Const]> {

@lcnr lcnr Feb 14, 2026

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same here

match self {
ValTreeKind::Branch(branch) => Some(&**branch),
ValTreeKind::Branch(branch) => Some(branch.as_slice()),
ValTreeKind::Leaf(_) => None,
}
}
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_type_ir/src/flags.rs
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Expand Up @@ -482,8 +482,8 @@ impl<I: Interner> FlagComputation<I> {
match cv.valtree().kind() {
ty::ValTreeKind::Leaf(_) => (),
ty::ValTreeKind::Branch(cts) => {
for ct in cts {
self.add_const(*ct);
for ct in cts.iter() {
self.add_const(ct);
}
}
}
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_type_ir/src/interner.rs
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Expand Up @@ -150,6 +150,7 @@ pub trait Interner:

// Kinds of consts
type Const: Const<Self>;
type Consts: Copy + Debug + Hash + Eq + SliceLike<Item = Self::Const> + Default;
type ParamConst: Copy + Debug + Hash + Eq + ParamLike;
type ValueConst: ValueConst<Self>;
type ExprConst: ExprConst<Self>;
Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_type_ir/src/relate.rs
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Expand Up @@ -577,8 +577,9 @@ pub fn structurally_relate_consts<I: Interner, R: TypeRelation<I>>(
if branches_a.len() == branches_b.len() =>
{
branches_a
.into_iter()
.zip(branches_b)
.as_slice()
.iter()
.zip(branches_b.as_slice().iter())
.all(|(a, b)| relation.relate(*a, *b).is_ok())

@lcnr lcnr Feb 14, 2026

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Suggested change
.as_slice()
.iter()
.zip(branches_b.as_slice().iter())
.all(|(a, b)| relation.relate(*a, *b).is_ok())
.iter()
.zip(branches_b.iter())
.all(|(a, b)| relation.relate(a, b).is_ok())

}
_ => false,
Expand Down
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