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rust-bors merged 1 commit into from
Jul 20, 2026
+36 −67
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Separate InterpCx usage by ConstAnalysis phases #159586

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103 changes: 36 additions & 67 deletions compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
//! Currently, this pass only propagates scalar values.

use std::assert_matches;
use std::cell::RefCell;
use std::fmt::Formatter;

use rustc_abi::{BackendRepr, FIRST_VARIANT, FieldIdx, Size, VariantIdx};
Expand Down Expand Up @@ -70,7 +69,7 @@ impl<'tcx> crate::MirPass<'tcx> for DataflowConstProp {
.in_scope(|| ConstAnalysis::new(tcx, body, map).iterate_to_fixpoint(tcx, body, None));

// Collect results and patch the body afterwards.
let mut visitor = Collector::new(tcx, &body.local_decls);
let mut visitor = Collector::new(tcx, body);
debug_span!("collect").in_scope(|| visit_reachable_results(body, &const_, &mut visitor));
let mut patch = visitor.patch;
debug_span!("patch").in_scope(|| patch.visit_body_preserves_cfg(body));
Expand All @@ -89,7 +88,7 @@ struct ConstAnalysis<'a, 'tcx> {
map: Map<'tcx>,
tcx: TyCtxt<'tcx>,
local_decls: &'a LocalDecls<'tcx>,
ecx: RefCell<InterpCx<'tcx, DummyMachine>>,
ecx: InterpCx<'tcx, DummyMachine>,
typing_env: ty::TypingEnv<'tcx>,
}

Expand Down Expand Up @@ -157,7 +156,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
map,
tcx,
local_decls: &body.local_decls,
ecx: RefCell::new(InterpCx::new(tcx, DUMMY_SP, typing_env, DummyMachine)),
ecx: InterpCx::new(tcx, DUMMY_SP, typing_env, DummyMachine),
typing_env,
}
}
Expand Down Expand Up @@ -412,7 +411,6 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
match self.eval_operand(operand, state) {
FlatSet::Elem(op) => self
.ecx
.borrow()
.int_to_int_or_float(&op, layout)
.discard_err()
.map_or(FlatSet::Top, |result| self.wrap_immediate(*result)),
Expand All @@ -427,7 +425,6 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
match self.eval_operand(operand, state) {
FlatSet::Elem(op) => self
.ecx
.borrow()
.float_to_float_or_int(&op, layout)
.discard_err()
.map_or(FlatSet::Top, |result| self.wrap_immediate(*result)),
Expand Down Expand Up @@ -458,7 +455,6 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
match self.eval_operand(operand, state) {
FlatSet::Elem(value) => self
.ecx
.borrow()
.unary_op(*op, &value)
.discard_err()
.map_or(FlatSet::Top, |val| self.wrap_immediate(*val)),
Expand Down Expand Up @@ -547,11 +543,8 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
}
}
Operand::Constant(constant) => {
if let Some(constant) = self
.ecx
.borrow()
.eval_mir_constant(&constant.const_, constant.span, None)
.discard_err()
if let Some(constant) =
self.ecx.eval_mir_constant(&constant.const_, constant.span, None).discard_err()
{
self.assign_constant(state, place, constant, &[]);
}
Expand Down Expand Up @@ -581,9 +574,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
return;
}
}
operand = if let Some(operand) =
self.ecx.borrow().project(&operand, proj_elem).discard_err()
{
operand = if let Some(operand) = self.ecx.project(&operand, proj_elem).discard_err() {
operand
} else {
return;
Expand All @@ -594,22 +585,17 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
place,
operand,
&mut |elem, op| match elem {
TrackElem::Field(idx) => self.ecx.borrow().project_field(op, idx).discard_err(),
TrackElem::Variant(idx) => {
self.ecx.borrow().project_downcast(op, idx).discard_err()
}
TrackElem::Field(idx) => self.ecx.project_field(op, idx).discard_err(),
TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).discard_err(),
TrackElem::Discriminant => {
let variant = self.ecx.borrow().read_discriminant(op).discard_err()?;
let discr_value = self
.ecx
.borrow()
.discriminant_for_variant(op.layout.ty, variant)
.discard_err()?;
let variant = self.ecx.read_discriminant(op).discard_err()?;
let discr_value =
self.ecx.discriminant_for_variant(op.layout.ty, variant).discard_err()?;
Some(discr_value.into())
}
TrackElem::DerefLen => {
let op: OpTy<'_> = self.ecx.borrow().deref_pointer(op).discard_err()?.into();
let len_usize = op.len(&self.ecx.borrow()).discard_err()?;
let op: OpTy<'_> = self.ecx.deref_pointer(op).discard_err()?.into();
let len_usize = op.len(&self.ecx).discard_err()?;
let layout = self
.tcx
.layout_of(self.typing_env.as_query_input(self.tcx.types.usize))
Expand All @@ -618,7 +604,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
}
},
&mut |place, op| {
if let Some(imm) = self.ecx.borrow().read_immediate_raw(op).discard_err()
if let Some(imm) = self.ecx.read_immediate_raw(op).discard_err()
&& let Some(imm) = imm.right()
{
let elem = self.wrap_immediate(*imm);
Expand All @@ -642,7 +628,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
(FlatSet::Bottom, _) | (_, FlatSet::Bottom) => (FlatSet::Bottom, FlatSet::Bottom),
// Both sides are known, do the actual computation.
(FlatSet::Elem(left), FlatSet::Elem(right)) => {
match self.ecx.borrow().binary_op(op, &left, &right).discard_err() {
match self.ecx.binary_op(op, &left, &right).discard_err() {
// Ideally this would return an Immediate, since it's sometimes
// a pair and sometimes not. But as a hack we always return a pair
// and just make the 2nd component `Bottom` when it does not exist.
Expand Down Expand Up @@ -715,11 +701,8 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
return None;
}
let enum_ty_layout = self.tcx.layout_of(self.typing_env.as_query_input(enum_ty)).ok()?;
let discr_value = self
.ecx
.borrow()
.discriminant_for_variant(enum_ty_layout.ty, variant_index)
.discard_err()?;
let discr_value =
self.ecx.discriminant_for_variant(enum_ty_layout.ty, variant_index).discard_err()?;
Some(discr_value.to_scalar())
}

Expand Down Expand Up @@ -781,23 +764,27 @@ impl<'tcx> Patch<'tcx> {
struct Collector<'a, 'tcx> {
patch: Patch<'tcx>,
local_decls: &'a LocalDecls<'tcx>,
ecx: InterpCx<'tcx, DummyMachine>,
}

impl<'a, 'tcx> Collector<'a, 'tcx> {
pub(crate) fn new(tcx: TyCtxt<'tcx>, local_decls: &'a LocalDecls<'tcx>) -> Self {
Self { patch: Patch::new(tcx), local_decls }
pub(crate) fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>) -> Self {
Self {
patch: Patch::new(tcx),
local_decls: &body.local_decls,
ecx: InterpCx::new(tcx, DUMMY_SP, body.typing_env(tcx), DummyMachine),
}
}

#[instrument(level = "trace", skip(self, ecx, map), ret)]
#[instrument(level = "trace", skip(self, map), ret)]
fn try_make_constant(
&self,
ecx: &mut InterpCx<'tcx, DummyMachine>,
&mut self,
place: Place<'tcx>,
state: &State<FlatSet<Scalar>>,
map: &Map<'tcx>,
) -> Option<Const<'tcx>> {
let ty = place.ty(self.local_decls, self.patch.tcx).ty;
let layout = ecx.layout_of(ty).ok()?;
let layout = self.ecx.layout_of(ty).ok()?;

if layout.is_zst() {
return Some(Const::zero_sized(ty));
Expand All @@ -815,7 +802,8 @@ impl<'a, 'tcx> Collector<'a, 'tcx> {
}

if matches!(layout.backend_repr, BackendRepr::Scalar(..) | BackendRepr::ScalarPair { .. }) {
let alloc_id = ecx
let alloc_id = self
.ecx
.intern_with_temp_alloc(layout, |ecx, dest| {
try_write_constant(ecx, dest, place, ty, state, map)
})
Expand Down Expand Up @@ -960,13 +948,8 @@ impl<'tcx> ResultsVisitor<'tcx, ConstAnalysis<'_, 'tcx>> for Collector<'_, 'tcx>
) {
match &statement.kind {
StatementKind::Assign((_, rvalue)) => {
OperandCollector {
state,
visitor: self,
ecx: &mut analysis.ecx.borrow_mut(),
map: &analysis.map,
}
.visit_rvalue(rvalue, location);
OperandCollector { state, visitor: self, map: &analysis.map }
.visit_rvalue(rvalue, location);
}
_ => (),
}
Expand All @@ -985,12 +968,7 @@ impl<'tcx> ResultsVisitor<'tcx, ConstAnalysis<'_, 'tcx>> for Collector<'_, 'tcx>
// Don't overwrite the assignment if it already uses a constant (to keep the span).
}
StatementKind::Assign((place, _)) => {
if let Some(value) = self.try_make_constant(
&mut analysis.ecx.borrow_mut(),
place,
state,
&analysis.map,
) {
if let Some(value) = self.try_make_constant(place, state, &analysis.map) {
self.patch.assignments.insert(location, value);
}
}
Expand All @@ -1005,13 +983,8 @@ impl<'tcx> ResultsVisitor<'tcx, ConstAnalysis<'_, 'tcx>> for Collector<'_, 'tcx>
terminator: &Terminator<'tcx>,
location: Location,
) {
OperandCollector {
state,
visitor: self,
ecx: &mut analysis.ecx.borrow_mut(),
map: &analysis.map,
}
.visit_terminator(terminator, location);
OperandCollector { state, visitor: self, map: &analysis.map }
.visit_terminator(terminator, location);
}
}

Expand Down Expand Up @@ -1070,7 +1043,6 @@ impl<'tcx> MutVisitor<'tcx> for Patch<'tcx> {
struct OperandCollector<'a, 'b, 'tcx> {
state: &'a State<FlatSet<Scalar>>,
visitor: &'a mut Collector<'b, 'tcx>,
ecx: &'a mut InterpCx<'tcx, DummyMachine>,
map: &'a Map<'tcx>,
}

Expand All @@ -1083,18 +1055,15 @@ impl<'tcx> Visitor<'tcx> for OperandCollector<'_, '_, 'tcx> {
location: Location,
) {
if let PlaceElem::Index(local) = elem
&& let Some(value) =
self.visitor.try_make_constant(self.ecx, local.into(), self.state, self.map)
&& let Some(value) = self.visitor.try_make_constant(local.into(), self.state, self.map)
{
self.visitor.patch.before_effect.insert((location, local.into()), value);
}
}

fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
if let Some(place) = operand.place() {
if let Some(value) =
self.visitor.try_make_constant(self.ecx, place, self.state, self.map)
{
if let Some(value) = self.visitor.try_make_constant(place, self.state, self.map) {
self.visitor.patch.before_effect.insert((location, place), value);
} else if !place.projection.is_empty() {
// Try to propagate into `Index` projections.
Expand Down
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