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Auto merge of rust-lang#135709 - lqd:bring-back-len, r=compiler-errors
Temporarily bring back `Rvalue::Len` r? `@compiler-errors` as requested in rust-lang#135671 (comment) > However, in the mean time, I'd rather we not crunch trying to find and more importantly validate the soundness of a solution 🤔 Agreed. To fix the IMO P-critical rust-lang#135671 for which we somehow didn't have test coverage, this PR temporarily reverts: - rust-lang#133734 - its bugfix rust-lang#134371 - rust-lang#134330 cc `@scottmcm` I added the few samples from that issue as a test, but we can add more in the future, in particular it seems `@steffahn` [will work on that](rust-lang#135671 (comment)). Fixes rust-lang#135671. And if we want to land this, it should also be nominated for beta backport.
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Diff for: ‎compiler/rustc_borrowck/src/lib.rs

+8-2
Original file line numberDiff line numberDiff line change
@@ -829,6 +829,7 @@ use self::ReadOrWrite::{Activation, Read, Reservation, Write};
829829

830830
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
831831
enum ArtificialField {
832+
ArrayLength,
832833
FakeBorrow,
833834
}
834835

@@ -1338,11 +1339,16 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, '_, 'tcx> {
13381339
);
13391340
}
13401341

1341-
&Rvalue::Discriminant(place) => {
1342+
&(Rvalue::Len(place) | Rvalue::Discriminant(place)) => {
1343+
let af = match *rvalue {
1344+
Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
1345+
Rvalue::Discriminant(..) => None,
1346+
_ => unreachable!(),
1347+
};
13421348
self.access_place(
13431349
location,
13441350
(place, span),
1345-
(Shallow(None), Read(ReadKind::Copy)),
1351+
(Shallow(af), Read(ReadKind::Copy)),
13461352
LocalMutationIsAllowed::No,
13471353
state,
13481354
);

Diff for: ‎compiler/rustc_borrowck/src/places_conflict.rs

+2-1
Original file line numberDiff line numberDiff line change
@@ -203,7 +203,8 @@ fn place_components_conflict<'tcx>(
203203
let base_ty = base.ty(body, tcx).ty;
204204

205205
match (elem, base_ty.kind(), access) {
206-
(_, _, Shallow(Some(ArtificialField::FakeBorrow))) => {
206+
(_, _, Shallow(Some(ArtificialField::ArrayLength)))
207+
| (_, _, Shallow(Some(ArtificialField::FakeBorrow))) => {
207208
// The array length is like additional fields on the
208209
// type; it does not overlap any existing data there.
209210
// Furthermore, if cannot actually be a prefix of any

Diff for: ‎compiler/rustc_borrowck/src/polonius/legacy/loan_invalidations.rs

+7-2
Original file line numberDiff line numberDiff line change
@@ -300,11 +300,16 @@ impl<'a, 'tcx> LoanInvalidationsGenerator<'a, 'tcx> {
300300
self.consume_operand(location, op);
301301
}
302302

303-
&Rvalue::Discriminant(place) => {
303+
&(Rvalue::Len(place) | Rvalue::Discriminant(place)) => {
304+
let af = match rvalue {
305+
Rvalue::Len(..) => Some(ArtificialField::ArrayLength),
306+
Rvalue::Discriminant(..) => None,
307+
_ => unreachable!(),
308+
};
304309
self.access_place(
305310
location,
306311
place,
307-
(Shallow(None), Read(ReadKind::Copy)),
312+
(Shallow(af), Read(ReadKind::Copy)),
308313
LocalMutationIsAllowed::No,
309314
);
310315
}

Diff for: ‎compiler/rustc_borrowck/src/type_check/mod.rs

+2
Original file line numberDiff line numberDiff line change
@@ -2235,6 +2235,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
22352235

22362236
Rvalue::RawPtr(..)
22372237
| Rvalue::ThreadLocalRef(..)
2238+
| Rvalue::Len(..)
22382239
| Rvalue::Discriminant(..)
22392240
| Rvalue::NullaryOp(NullOp::OffsetOf(..), _) => {}
22402241
}
@@ -2250,6 +2251,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
22502251
| Rvalue::Repeat(..)
22512252
| Rvalue::Ref(..)
22522253
| Rvalue::RawPtr(..)
2254+
| Rvalue::Len(..)
22532255
| Rvalue::Cast(..)
22542256
| Rvalue::ShallowInitBox(..)
22552257
| Rvalue::BinaryOp(..)

Diff for: ‎compiler/rustc_codegen_cranelift/src/base.rs

+6
Original file line numberDiff line numberDiff line change
@@ -828,6 +828,12 @@ fn codegen_stmt<'tcx>(
828828
fx.bcx.ins().nop();
829829
}
830830
}
831+
Rvalue::Len(place) => {
832+
let place = codegen_place(fx, place);
833+
let usize_layout = fx.layout_of(fx.tcx.types.usize);
834+
let len = codegen_array_len(fx, place);
835+
lval.write_cvalue(fx, CValue::by_val(len, usize_layout));
836+
}
831837
Rvalue::ShallowInitBox(ref operand, content_ty) => {
832838
let content_ty = fx.monomorphize(content_ty);
833839
let box_layout = fx.layout_of(Ty::new_box(fx.tcx, content_ty));

Diff for: ‎compiler/rustc_codegen_ssa/src/mir/rvalue.rs

+28-1
Original file line numberDiff line numberDiff line change
@@ -10,9 +10,9 @@ use rustc_session::config::OptLevel;
1010
use rustc_span::{DUMMY_SP, Span};
1111
use tracing::{debug, instrument};
1212

13-
use super::FunctionCx;
1413
use super::operand::{OperandRef, OperandValue};
1514
use super::place::PlaceRef;
15+
use super::{FunctionCx, LocalRef};
1616
use crate::common::IntPredicate;
1717
use crate::traits::*;
1818
use crate::{MemFlags, base};
@@ -607,6 +607,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
607607
self.codegen_place_to_pointer(bx, place, mk_ptr)
608608
}
609609

610+
mir::Rvalue::Len(place) => {
611+
let size = self.evaluate_array_len(bx, place);
612+
OperandRef {
613+
val: OperandValue::Immediate(size),
614+
layout: bx.cx().layout_of(bx.tcx().types.usize),
615+
}
616+
}
617+
610618
mir::Rvalue::BinaryOp(op_with_overflow, box (ref lhs, ref rhs))
611619
if let Some(op) = op_with_overflow.overflowing_to_wrapping() =>
612620
{
@@ -806,6 +814,24 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
806814
}
807815
}
808816

817+
fn evaluate_array_len(&mut self, bx: &mut Bx, place: mir::Place<'tcx>) -> Bx::Value {
818+
// ZST are passed as operands and require special handling
819+
// because codegen_place() panics if Local is operand.
820+
if let Some(index) = place.as_local() {
821+
if let LocalRef::Operand(op) = self.locals[index] {
822+
if let ty::Array(_, n) = op.layout.ty.kind() {
823+
let n = n
824+
.try_to_target_usize(bx.tcx())
825+
.expect("expected monomorphic const in codegen");
826+
return bx.cx().const_usize(n);
827+
}
828+
}
829+
}
830+
// use common size calculation for non zero-sized types
831+
let cg_value = self.codegen_place(bx, place.as_ref());
832+
cg_value.len(bx.cx())
833+
}
834+
809835
/// Codegen an `Rvalue::RawPtr` or `Rvalue::Ref`
810836
fn codegen_place_to_pointer(
811837
&mut self,
@@ -1077,6 +1103,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
10771103
mir::Rvalue::Ref(..) |
10781104
mir::Rvalue::CopyForDeref(..) |
10791105
mir::Rvalue::RawPtr(..) |
1106+
mir::Rvalue::Len(..) |
10801107
mir::Rvalue::Cast(..) | // (*)
10811108
mir::Rvalue::ShallowInitBox(..) | // (*)
10821109
mir::Rvalue::BinaryOp(..) |

Diff for: ‎compiler/rustc_const_eval/src/check_consts/check.rs

+7-21
Original file line numberDiff line numberDiff line change
@@ -495,7 +495,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
495495
Rvalue::Use(_)
496496
| Rvalue::CopyForDeref(..)
497497
| Rvalue::Repeat(..)
498-
| Rvalue::Discriminant(..) => {}
498+
| Rvalue::Discriminant(..)
499+
| Rvalue::Len(_) => {}
499500

500501
Rvalue::Aggregate(kind, ..) => {
501502
if let AggregateKind::Coroutine(def_id, ..) = kind.as_ref()
@@ -579,27 +580,12 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
579580
) => {}
580581
Rvalue::ShallowInitBox(_, _) => {}
581582

582-
Rvalue::UnaryOp(op, operand) => {
583+
Rvalue::UnaryOp(_, operand) => {
583584
let ty = operand.ty(self.body, self.tcx);
584-
match op {
585-
UnOp::Not | UnOp::Neg => {
586-
if is_int_bool_float_or_char(ty) {
587-
// Int, bool, float, and char operations are fine.
588-
} else {
589-
span_bug!(
590-
self.span,
591-
"non-primitive type in `Rvalue::UnaryOp{op:?}`: {ty:?}",
592-
);
593-
}
594-
}
595-
UnOp::PtrMetadata => {
596-
if !ty.is_ref() && !ty.is_unsafe_ptr() {
597-
span_bug!(
598-
self.span,
599-
"non-pointer type in `Rvalue::UnaryOp({op:?})`: {ty:?}",
600-
);
601-
}
602-
}
585+
if is_int_bool_float_or_char(ty) {
586+
// Int, bool, float, and char operations are fine.
587+
} else {
588+
span_bug!(self.span, "non-primitive type in `Rvalue::UnaryOp`: {:?}", ty);
603589
}
604590
}
605591

Diff for: ‎compiler/rustc_const_eval/src/check_consts/qualifs.rs

+3-1
Original file line numberDiff line numberDiff line change
@@ -230,7 +230,9 @@ where
230230
Q::in_any_value_of_ty(cx, rvalue.ty(cx.body, cx.tcx))
231231
}
232232

233-
Rvalue::Discriminant(place) => in_place::<Q, _>(cx, in_local, place.as_ref()),
233+
Rvalue::Discriminant(place) | Rvalue::Len(place) => {
234+
in_place::<Q, _>(cx, in_local, place.as_ref())
235+
}
234236

235237
Rvalue::CopyForDeref(place) => in_place::<Q, _>(cx, in_local, place.as_ref()),
236238

Diff for: ‎compiler/rustc_const_eval/src/check_consts/resolver.rs

+1
Original file line numberDiff line numberDiff line change
@@ -197,6 +197,7 @@ where
197197
| mir::Rvalue::CopyForDeref(..)
198198
| mir::Rvalue::ThreadLocalRef(..)
199199
| mir::Rvalue::Repeat(..)
200+
| mir::Rvalue::Len(..)
200201
| mir::Rvalue::BinaryOp(..)
201202
| mir::Rvalue::NullaryOp(..)
202203
| mir::Rvalue::UnaryOp(..)

Diff for: ‎compiler/rustc_const_eval/src/interpret/step.rs

+9-12
Original file line numberDiff line numberDiff line change
@@ -9,13 +9,12 @@ use rustc_middle::ty::layout::FnAbiOf;
99
use rustc_middle::ty::{self, Instance, Ty};
1010
use rustc_middle::{bug, mir, span_bug};
1111
use rustc_span::source_map::Spanned;
12-
use rustc_span::{DesugaringKind, Span};
1312
use rustc_target::callconv::FnAbi;
1413
use tracing::{info, instrument, trace};
1514

1615
use super::{
1716
FnArg, FnVal, ImmTy, Immediate, InterpCx, InterpResult, Machine, MemPlaceMeta, PlaceTy,
18-
Projectable, interp_ok, throw_ub,
17+
Projectable, Scalar, interp_ok, throw_ub,
1918
};
2019
use crate::util;
2120

@@ -81,9 +80,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
8180
use rustc_middle::mir::StatementKind::*;
8281

8382
match &stmt.kind {
84-
Assign(box (place, rvalue)) => {
85-
self.eval_rvalue_into_place(rvalue, *place, stmt.source_info.span)?
86-
}
83+
Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,
8784

8885
SetDiscriminant { place, variant_index } => {
8986
let dest = self.eval_place(**place)?;
@@ -162,7 +159,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
162159
&mut self,
163160
rvalue: &mir::Rvalue<'tcx>,
164161
place: mir::Place<'tcx>,
165-
span: Span,
166162
) -> InterpResult<'tcx> {
167163
let dest = self.eval_place(place)?;
168164
// FIXME: ensure some kind of non-aliasing between LHS and RHS?
@@ -218,6 +214,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
218214
self.write_repeat(operand, &dest)?;
219215
}
220216

217+
Len(place) => {
218+
let src = self.eval_place(place)?;
219+
let len = src.len(self)?;
220+
self.write_scalar(Scalar::from_target_usize(len, self), &dest)?;
221+
}
222+
221223
Ref(_, borrow_kind, place) => {
222224
let src = self.eval_place(place)?;
223225
let place = self.force_allocation(&src)?;
@@ -248,13 +250,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
248250
let src = self.eval_place(place)?;
249251
let place = self.force_allocation(&src)?;
250252
let mut val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
251-
if !place_base_raw
252-
&& span.desugaring_kind() != Some(DesugaringKind::IndexBoundsCheckReborrow)
253-
{
253+
if !place_base_raw {
254254
// If this was not already raw, it needs retagging.
255-
// As a special hack, we exclude the desugared `PtrMetadata(&raw const *_n)`
256-
// from indexing. (Really we should not do any retag on `&raw` but that does not
257-
// currently work with Stacked Borrows.)
258255
val = M::retag_ptr_value(self, mir::RetagKind::Raw, &val)?;
259256
}
260257
self.write_immediate(*val, &dest)?;

Diff for: ‎compiler/rustc_middle/src/mir/consts.rs

-3
Original file line numberDiff line numberDiff line change
@@ -467,9 +467,6 @@ impl<'tcx> Const<'tcx> {
467467
let const_val = tcx.valtree_to_const_val((ty, valtree));
468468
Self::Val(const_val, ty)
469469
}
470-
ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, args }) => {
471-
Self::Unevaluated(UnevaluatedConst { def, args, promoted: None }, ty)
472-
}
473470
_ => Self::Ty(ty, c),
474471
}
475472
}

Diff for: ‎compiler/rustc_middle/src/mir/pretty.rs

+1
Original file line numberDiff line numberDiff line change
@@ -1068,6 +1068,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
10681068
pretty_print_const(b, fmt, false)?;
10691069
write!(fmt, "]")
10701070
}
1071+
Len(ref a) => write!(fmt, "Len({a:?})"),
10711072
Cast(ref kind, ref place, ref ty) => {
10721073
with_no_trimmed_paths!(write!(fmt, "{place:?} as {ty} ({kind:?})"))
10731074
}

Diff for: ‎compiler/rustc_middle/src/mir/statement.rs

+1
Original file line numberDiff line numberDiff line change
@@ -424,6 +424,7 @@ impl<'tcx> Rvalue<'tcx> {
424424
| Rvalue::Ref(_, _, _)
425425
| Rvalue::ThreadLocalRef(_)
426426
| Rvalue::RawPtr(_, _)
427+
| Rvalue::Len(_)
427428
| Rvalue::Cast(
428429
CastKind::IntToInt
429430
| CastKind::FloatToInt

Diff for: ‎compiler/rustc_middle/src/mir/syntax.rs

+10
Original file line numberDiff line numberDiff line change
@@ -1351,6 +1351,16 @@ pub enum Rvalue<'tcx> {
13511351
/// model.
13521352
RawPtr(Mutability, Place<'tcx>),
13531353

1354+
/// Yields the length of the place, as a `usize`.
1355+
///
1356+
/// If the type of the place is an array, this is the array length. For slices (`[T]`, not
1357+
/// `&[T]`) this accesses the place's metadata to determine the length. This rvalue is
1358+
/// ill-formed for places of other types.
1359+
///
1360+
/// This cannot be a `UnOp(PtrMetadata, _)` because that expects a value, and we only
1361+
/// have a place, and `UnOp(PtrMetadata, RawPtr(place))` is not a thing.
1362+
Len(Place<'tcx>),
1363+
13541364
/// Performs essentially all of the casts that can be performed via `as`.
13551365
///
13561366
/// This allows for casts from/to a variety of types.

Diff for: ‎compiler/rustc_middle/src/mir/tcx.rs

+1
Original file line numberDiff line numberDiff line change
@@ -210,6 +210,7 @@ impl<'tcx> Rvalue<'tcx> {
210210
let place_ty = place.ty(local_decls, tcx).ty;
211211
Ty::new_ptr(tcx, place_ty, mutability)
212212
}
213+
Rvalue::Len(..) => tcx.types.usize,
213214
Rvalue::Cast(.., ty) => ty,
214215
Rvalue::BinaryOp(op, box (ref lhs, ref rhs)) => {
215216
let lhs_ty = lhs.ty(local_decls, tcx);

Diff for: ‎compiler/rustc_middle/src/mir/visit.rs

+8
Original file line numberDiff line numberDiff line change
@@ -695,6 +695,14 @@ macro_rules! make_mir_visitor {
695695
self.visit_place(path, ctx, location);
696696
}
697697

698+
Rvalue::Len(path) => {
699+
self.visit_place(
700+
path,
701+
PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
702+
location
703+
);
704+
}
705+
698706
Rvalue::Cast(_cast_kind, operand, ty) => {
699707
self.visit_operand(operand, location);
700708
self.visit_ty($(& $mutability)? *ty, TyContext::Location(location));

Diff for: ‎compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs

+1
Original file line numberDiff line numberDiff line change
@@ -246,6 +246,7 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
246246
let offset = self.parse_operand(args[1])?;
247247
Ok(Rvalue::BinaryOp(BinOp::Offset, Box::new((ptr, offset))))
248248
},
249+
@call(mir_len, args) => Ok(Rvalue::Len(self.parse_place(args[0])?)),
249250
@call(mir_ptr_metadata, args) => Ok(Rvalue::UnaryOp(UnOp::PtrMetadata, self.parse_operand(args[0])?)),
250251
@call(mir_copy_for_deref, args) => Ok(Rvalue::CopyForDeref(self.parse_place(args[0])?)),
251252
ExprKind::Borrow { borrow_kind, arg } => Ok(

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