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//! Propagates constants for early reporting of statically known
//! assertion failures
use std::fmt::Debug;
use either::Left;
use rustc_const_eval::interpret::Immediate;
use rustc_const_eval::interpret::{
InterpCx, InterpResult, MemoryKind, OpTy, Scalar, StackPopCleanup,
};
use rustc_const_eval::ReportErrorExt;
use rustc_hir::def::DefKind;
use rustc_hir::HirId;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::Visitor;
use rustc_middle::mir::*;
use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::{
self, ConstInt, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitableExt,
};
use rustc_span::Span;
use rustc_target::abi::{HasDataLayout, Size, TargetDataLayout};
use rustc_trait_selection::traits;
use crate::const_prop::CanConstProp;
use crate::const_prop::ConstPropMachine;
use crate::const_prop::ConstPropMode;
use crate::errors::AssertLint;
use crate::MirLint;
/// The maximum number of bytes that we'll allocate space for a local or the return value.
/// Needed for #66397, because otherwise we eval into large places and that can cause OOM or just
/// Severely regress performance.
const MAX_ALLOC_LIMIT: u64 = 1024;
pub struct ConstProp;
impl<'tcx> MirLint<'tcx> for ConstProp {
fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
if body.tainted_by_errors.is_some() {
return;
}
// will be evaluated by miri and produce its errors there
if body.source.promoted.is_some() {
return;
}
let def_id = body.source.def_id().expect_local();
let is_fn_like = tcx.def_kind(def_id).is_fn_like();
let is_assoc_const = tcx.def_kind(def_id) == DefKind::AssocConst;
// Only run const prop on functions, methods, closures and associated constants
if !is_fn_like && !is_assoc_const {
// skip anon_const/statics/consts because they'll be evaluated by miri anyway
trace!("ConstProp skipped for {:?}", def_id);
return;
}
let is_generator = tcx.type_of(def_id.to_def_id()).instantiate_identity().is_generator();
// FIXME(welseywiser) const prop doesn't work on generators because of query cycles
// computing their layout.
if is_generator {
trace!("ConstProp skipped for generator {:?}", def_id);
return;
}
// Check if it's even possible to satisfy the 'where' clauses
// for this item.
// This branch will never be taken for any normal function.
// However, it's possible to `#!feature(trivial_bounds)]` to write
// a function with impossible to satisfy clauses, e.g.:
// `fn foo() where String: Copy {}`
//
// We don't usually need to worry about this kind of case,
// since we would get a compilation error if the user tried
// to call it. However, since we can do const propagation
// even without any calls to the function, we need to make
// sure that it even makes sense to try to evaluate the body.
// If there are unsatisfiable where clauses, then all bets are
// off, and we just give up.
//
// We manually filter the predicates, skipping anything that's not
// "global". We are in a potentially generic context
// (e.g. we are evaluating a function without substituting generic
// parameters, so this filtering serves two purposes:
//
// 1. We skip evaluating any predicates that we would
// never be able prove are unsatisfiable (e.g. `<T as Foo>`
// 2. We avoid trying to normalize predicates involving generic
// parameters (e.g. `<T as Foo>::MyItem`). This can confuse
// the normalization code (leading to cycle errors), since
// it's usually never invoked in this way.
let predicates = tcx
.predicates_of(def_id.to_def_id())
.predicates
.iter()
.filter_map(|(p, _)| if p.is_global() { Some(*p) } else { None });
if traits::impossible_predicates(tcx, traits::elaborate(tcx, predicates).collect()) {
trace!("ConstProp skipped for {:?}: found unsatisfiable predicates", def_id);
return;
}
trace!("ConstProp starting for {:?}", def_id);
// FIXME(oli-obk, eddyb) Optimize locals (or even local paths) to hold
// constants, instead of just checking for const-folding succeeding.
// That would require a uniform one-def no-mutation analysis
// and RPO (or recursing when needing the value of a local).
let mut linter = ConstPropagator::new(body, tcx);
linter.visit_body(body);
trace!("ConstProp done for {:?}", def_id);
}
}
/// Finds optimization opportunities on the MIR.
struct ConstPropagator<'mir, 'tcx> {
ecx: InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>,
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
worklist: Vec<BasicBlock>,
visited_blocks: BitSet<BasicBlock>,
}
impl<'tcx> LayoutOfHelpers<'tcx> for ConstPropagator<'_, 'tcx> {
type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
#[inline]
fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
err
}
}
impl HasDataLayout for ConstPropagator<'_, '_> {
#[inline]
fn data_layout(&self) -> &TargetDataLayout {
&self.tcx.data_layout
}
}
impl<'tcx> ty::layout::HasTyCtxt<'tcx> for ConstPropagator<'_, 'tcx> {
#[inline]
fn tcx(&self) -> TyCtxt<'tcx> {
self.tcx
}
}
impl<'tcx> ty::layout::HasParamEnv<'tcx> for ConstPropagator<'_, 'tcx> {
#[inline]
fn param_env(&self) -> ty::ParamEnv<'tcx> {
self.param_env
}
}
impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
fn new(body: &'mir Body<'tcx>, tcx: TyCtxt<'tcx>) -> ConstPropagator<'mir, 'tcx> {
let def_id = body.source.def_id();
let args = &GenericArgs::identity_for_item(tcx, def_id);
let param_env = tcx.param_env_reveal_all_normalized(def_id);
let can_const_prop = CanConstProp::check(tcx, param_env, body);
let mut ecx = InterpCx::new(
tcx,
tcx.def_span(def_id),
param_env,
ConstPropMachine::new(can_const_prop),
);
let ret_layout = ecx
.layout_of(body.bound_return_ty().instantiate(tcx, args))
.ok()
// Don't bother allocating memory for large values.
// I don't know how return types can seem to be unsized but this happens in the
// `type/type-unsatisfiable.rs` test.
.filter(|ret_layout| {
ret_layout.is_sized() && ret_layout.size < Size::from_bytes(MAX_ALLOC_LIMIT)
})
.unwrap_or_else(|| ecx.layout_of(tcx.types.unit).unwrap());
let ret = ecx
.allocate(ret_layout, MemoryKind::Stack)
.expect("couldn't perform small allocation")
.into();
ecx.push_stack_frame(
Instance::new(def_id, args),
body,
&ret,
StackPopCleanup::Root { cleanup: false },
)
.expect("failed to push initial stack frame");
for local in body.local_decls.indices() {
// Mark everything initially live.
// This is somewhat dicey since some of them might be unsized and it is incoherent to
// mark those as live... We rely on `local_to_place`/`local_to_op` in the interpreter
// stopping us before those unsized immediates can cause issues deeper in the
// interpreter.
ecx.frame_mut().locals[local].make_live_uninit();
}
ConstPropagator {
ecx,
tcx,
param_env,
worklist: vec![START_BLOCK],
visited_blocks: BitSet::new_empty(body.basic_blocks.len()),
}
}
fn body(&self) -> &'mir Body<'tcx> {
self.ecx.frame().body
}
fn local_decls(&self) -> &'mir LocalDecls<'tcx> {
&self.body().local_decls
}
fn get_const(&self, place: Place<'tcx>) -> Option<OpTy<'tcx>> {
let op = match self.ecx.eval_place_to_op(place, None) {
Ok(op) => {
if op
.as_mplace_or_imm()
.right()
.is_some_and(|imm| matches!(*imm, Immediate::Uninit))
{
// Make sure nobody accidentally uses this value.
return None;
}
op
}
Err(e) => {
trace!("get_const failed: {:?}", e.into_kind().debug());
return None;
}
};
// Try to read the local as an immediate so that if it is representable as a scalar, we can
// handle it as such, but otherwise, just return the value as is.
Some(match self.ecx.read_immediate_raw(&op) {
Ok(Left(imm)) => imm.into(),
_ => op,
})
}
/// Remove `local` from the pool of `Locals`. Allows writing to them,
/// but not reading from them anymore.
fn remove_const(ecx: &mut InterpCx<'mir, 'tcx, ConstPropMachine<'mir, 'tcx>>, local: Local) {
ecx.frame_mut().locals[local].make_live_uninit();
ecx.machine.written_only_inside_own_block_locals.remove(&local);
}
fn lint_root(&self, source_info: SourceInfo) -> Option<HirId> {
source_info.scope.lint_root(&self.body().source_scopes)
}
fn use_ecx<F, T>(&mut self, location: Location, f: F) -> Option<T>
where
F: FnOnce(&mut Self) -> InterpResult<'tcx, T>,
{
// Overwrite the PC -- whatever the interpreter does to it does not make any sense anyway.
self.ecx.frame_mut().loc = Left(location);
match f(self) {
Ok(val) => Some(val),
Err(error) => {
trace!("InterpCx operation failed: {:?}", error);
// Some errors shouldn't come up because creating them causes
// an allocation, which we should avoid. When that happens,
// dedicated error variants should be introduced instead.
assert!(
!error.kind().formatted_string(),
"const-prop encountered formatting error: {}",
self.ecx.format_error(error),
);
None
}
}
}
/// Returns the value, if any, of evaluating `c`.
fn eval_constant(&mut self, c: &ConstOperand<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
// FIXME we need to revisit this for #67176
if c.has_param() {
return None;
}
// Normalization needed b/c const prop lint runs in
// `mir_drops_elaborated_and_const_checked`, which happens before
// optimized MIR. Only after optimizing the MIR can we guarantee
// that the `RevealAll` pass has happened and that the body's consts
// are normalized, so any call to resolve before that needs to be
// manually normalized.
let val = self.tcx.try_normalize_erasing_regions(self.param_env, c.const_).ok()?;
self.use_ecx(location, |this| this.ecx.eval_mir_constant(&val, Some(c.span), None))
}
/// Returns the value, if any, of evaluating `place`.
fn eval_place(&mut self, place: Place<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
trace!("eval_place(place={:?})", place);
self.use_ecx(location, |this| this.ecx.eval_place_to_op(place, None))
}
/// Returns the value, if any, of evaluating `op`. Calls upon `eval_constant`
/// or `eval_place`, depending on the variant of `Operand` used.
fn eval_operand(&mut self, op: &Operand<'tcx>, location: Location) -> Option<OpTy<'tcx>> {
match *op {
Operand::Constant(ref c) => self.eval_constant(c, location),
Operand::Move(place) | Operand::Copy(place) => self.eval_place(place, location),
}
}
fn report_assert_as_lint(&self, source_info: &SourceInfo, lint: AssertLint<impl Debug>) {
if let Some(lint_root) = self.lint_root(*source_info) {
self.tcx.emit_spanned_lint(lint.lint(), lint_root, source_info.span, lint);
}
}
fn check_unary_op(&mut self, op: UnOp, arg: &Operand<'tcx>, location: Location) -> Option<()> {
if let (val, true) = self.use_ecx(location, |this| {
let val = this.ecx.read_immediate(&this.ecx.eval_operand(arg, None)?)?;
let (_res, overflow) = this.ecx.overflowing_unary_op(op, &val)?;
Ok((val, overflow))
})? {
// `AssertKind` only has an `OverflowNeg` variant, so make sure that is
// appropriate to use.
assert_eq!(op, UnOp::Neg, "Neg is the only UnOp that can overflow");
let source_info = self.body().source_info(location);
self.report_assert_as_lint(
source_info,
AssertLint::ArithmeticOverflow(
source_info.span,
AssertKind::OverflowNeg(val.to_const_int()),
),
);
return None;
}
Some(())
}
fn check_binary_op(
&mut self,
op: BinOp,
left: &Operand<'tcx>,
right: &Operand<'tcx>,
location: Location,
) -> Option<()> {
let r = self.use_ecx(location, |this| {
this.ecx.read_immediate(&this.ecx.eval_operand(right, None)?)
});
let l = self
.use_ecx(location, |this| this.ecx.read_immediate(&this.ecx.eval_operand(left, None)?));
// Check for exceeding shifts *even if* we cannot evaluate the LHS.
if matches!(op, BinOp::Shr | BinOp::Shl) {
let r = r.clone()?;
// We need the type of the LHS. We cannot use `place_layout` as that is the type
// of the result, which for checked binops is not the same!
let left_ty = left.ty(self.local_decls(), self.tcx);
let left_size = self.ecx.layout_of(left_ty).ok()?.size;
let right_size = r.layout.size;
let r_bits = r.to_scalar().to_bits(right_size).ok();
if r_bits.is_some_and(|b| b >= left_size.bits() as u128) {
debug!("check_binary_op: reporting assert for {:?}", location);
let source_info = self.body().source_info(location);
let panic = AssertKind::Overflow(
op,
match l {
Some(l) => l.to_const_int(),
// Invent a dummy value, the diagnostic ignores it anyway
None => ConstInt::new(
ScalarInt::try_from_uint(1_u8, left_size).unwrap(),
left_ty.is_signed(),
left_ty.is_ptr_sized_integral(),
),
},
r.to_const_int(),
);
self.report_assert_as_lint(
source_info,
AssertLint::ArithmeticOverflow(source_info.span, panic),
);
return None;
}
}
if let (Some(l), Some(r)) = (l, r) {
// The remaining operators are handled through `overflowing_binary_op`.
if self.use_ecx(location, |this| {
let (_res, overflow) = this.ecx.overflowing_binary_op(op, &l, &r)?;
Ok(overflow)
})? {
let source_info = self.body().source_info(location);
self.report_assert_as_lint(
source_info,
AssertLint::ArithmeticOverflow(
source_info.span,
AssertKind::Overflow(op, l.to_const_int(), r.to_const_int()),
),
);
return None;
}
}
Some(())
}
fn check_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) -> Option<()> {
// Perform any special handling for specific Rvalue types.
// Generally, checks here fall into one of two categories:
// 1. Additional checking to provide useful lints to the user
// - In this case, we will do some validation and then fall through to the
// end of the function which evals the assignment.
// 2. Working around bugs in other parts of the compiler
// - In this case, we'll return `None` from this function to stop evaluation.
match rvalue {
// Additional checking: give lints to the user if an overflow would occur.
// We do this here and not in the `Assert` terminator as that terminator is
// only sometimes emitted (overflow checks can be disabled), but we want to always
// lint.
Rvalue::UnaryOp(op, arg) => {
trace!("checking UnaryOp(op = {:?}, arg = {:?})", op, arg);
self.check_unary_op(*op, arg, location)?;
}
Rvalue::BinaryOp(op, box (left, right)) => {
trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right);
self.check_binary_op(*op, left, right, location)?;
}
Rvalue::CheckedBinaryOp(op, box (left, right)) => {
trace!(
"checking CheckedBinaryOp(op = {:?}, left = {:?}, right = {:?})",
op,
left,
right
);
self.check_binary_op(*op, left, right, location)?;
}
// Do not try creating references (#67862)
Rvalue::AddressOf(_, place) | Rvalue::Ref(_, _, place) => {
trace!("skipping AddressOf | Ref for {:?}", place);
// This may be creating mutable references or immutable references to cells.
// If that happens, the pointed to value could be mutated via that reference.
// Since we aren't tracking references, the const propagator loses track of what
// value the local has right now.
// Thus, all locals that have their reference taken
// must not take part in propagation.
Self::remove_const(&mut self.ecx, place.local);
return None;
}
Rvalue::ThreadLocalRef(def_id) => {
trace!("skipping ThreadLocalRef({:?})", def_id);
return None;
}
// There's no other checking to do at this time.
Rvalue::Aggregate(..)
| Rvalue::Use(..)
| Rvalue::CopyForDeref(..)
| Rvalue::Repeat(..)
| Rvalue::Len(..)
| Rvalue::Cast(..)
| Rvalue::ShallowInitBox(..)
| Rvalue::Discriminant(..)
| Rvalue::NullaryOp(..) => {}
}
// FIXME we need to revisit this for #67176
if rvalue.has_param() {
return None;
}
if !rvalue.ty(self.local_decls(), self.tcx).is_sized(self.tcx, self.param_env) {
// the interpreter doesn't support unsized locals (only unsized arguments),
// but rustc does (in a kinda broken way), so we have to skip them here
return None;
}
Some(())
}
fn check_assertion(
&mut self,
expected: bool,
msg: &AssertKind<Operand<'tcx>>,
cond: &Operand<'tcx>,
location: Location,
) -> Option<!> {
let value = &self.eval_operand(&cond, location)?;
trace!("assertion on {:?} should be {:?}", value, expected);
let expected = Scalar::from_bool(expected);
let value_const = self.use_ecx(location, |this| this.ecx.read_scalar(value))?;
if expected != value_const {
// Poison all places this operand references so that further code
// doesn't use the invalid value
if let Some(place) = cond.place() {
Self::remove_const(&mut self.ecx, place.local);
}
enum DbgVal<T> {
Val(T),
Underscore,
}
impl<T: std::fmt::Debug> std::fmt::Debug for DbgVal<T> {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Val(val) => val.fmt(fmt),
Self::Underscore => fmt.write_str("_"),
}
}
}
let mut eval_to_int = |op| {
// This can be `None` if the lhs wasn't const propagated and we just
// triggered the assert on the value of the rhs.
self.eval_operand(op, location)
.and_then(|op| self.ecx.read_immediate(&op).ok())
.map_or(DbgVal::Underscore, |op| DbgVal::Val(op.to_const_int()))
};
let msg = match msg {
AssertKind::DivisionByZero(op) => AssertKind::DivisionByZero(eval_to_int(op)),
AssertKind::RemainderByZero(op) => AssertKind::RemainderByZero(eval_to_int(op)),
AssertKind::Overflow(bin_op @ (BinOp::Div | BinOp::Rem), op1, op2) => {
// Division overflow is *UB* in the MIR, and different than the
// other overflow checks.
AssertKind::Overflow(*bin_op, eval_to_int(op1), eval_to_int(op2))
}
AssertKind::BoundsCheck { ref len, ref index } => {
let len = eval_to_int(len);
let index = eval_to_int(index);
AssertKind::BoundsCheck { len, index }
}
// Remaining overflow errors are already covered by checks on the binary operators.
AssertKind::Overflow(..) | AssertKind::OverflowNeg(_) => return None,
// Need proper const propagator for these.
_ => return None,
};
let source_info = self.body().source_info(location);
self.report_assert_as_lint(
source_info,
AssertLint::UnconditionalPanic(source_info.span, msg),
);
}
None
}
fn ensure_not_propagated(&self, local: Local) {
if cfg!(debug_assertions) {
assert!(
self.get_const(local.into()).is_none()
|| self
.layout_of(self.local_decls()[local].ty)
.map_or(true, |layout| layout.is_zst()),
"failed to remove values for `{local:?}`, value={:?}",
self.get_const(local.into()),
)
}
}
}
impl<'tcx> Visitor<'tcx> for ConstPropagator<'_, 'tcx> {
fn visit_body(&mut self, body: &Body<'tcx>) {
while let Some(bb) = self.worklist.pop() {
if !self.visited_blocks.insert(bb) {
continue;
}
let data = &body.basic_blocks[bb];
self.visit_basic_block_data(bb, data);
}
}
fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
self.super_operand(operand, location);
}
fn visit_constant(&mut self, constant: &ConstOperand<'tcx>, location: Location) {
trace!("visit_constant: {:?}", constant);
self.super_constant(constant, location);
self.eval_constant(constant, location);
}
fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
self.super_assign(place, rvalue, location);
let Some(()) = self.check_rvalue(rvalue, location) else { return };
match self.ecx.machine.can_const_prop[place.local] {
// Do nothing if the place is indirect.
_ if place.is_indirect() => {}
ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
ConstPropMode::OnlyInsideOwnBlock | ConstPropMode::FullConstProp => {
if self
.use_ecx(location, |this| this.ecx.eval_rvalue_into_place(rvalue, *place))
.is_none()
{
// Const prop failed, so erase the destination, ensuring that whatever happens
// from here on, does not know about the previous value.
// This is important in case we have
// ```rust
// let mut x = 42;
// x = SOME_MUTABLE_STATIC;
// // x must now be uninit
// ```
// FIXME: we overzealously erase the entire local, because that's easier to
// implement.
trace!(
"propagation into {:?} failed.
Nuking the entire site from orbit, it's the only way to be sure",
place,
);
Self::remove_const(&mut self.ecx, place.local);
}
}
}
}
fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
trace!("visit_statement: {:?}", statement);
// We want to evaluate operands before any change to the assigned-to value,
// so we recurse first.
self.super_statement(statement, location);
match statement.kind {
StatementKind::SetDiscriminant { ref place, .. } => {
match self.ecx.machine.can_const_prop[place.local] {
// Do nothing if the place is indirect.
_ if place.is_indirect() => {}
ConstPropMode::NoPropagation => self.ensure_not_propagated(place.local),
ConstPropMode::FullConstProp | ConstPropMode::OnlyInsideOwnBlock => {
if self.use_ecx(location, |this| this.ecx.statement(statement)).is_some() {
trace!("propped discriminant into {:?}", place);
} else {
Self::remove_const(&mut self.ecx, place.local);
}
}
}
}
StatementKind::StorageLive(local) => {
let frame = self.ecx.frame_mut();
frame.locals[local].make_live_uninit();
}
StatementKind::StorageDead(local) => {
let frame = self.ecx.frame_mut();
// We don't actually track liveness, so the local remains live. But forget its value.
frame.locals[local].make_live_uninit();
}
_ => {}
}
}
fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
self.super_terminator(terminator, location);
match &terminator.kind {
TerminatorKind::Assert { expected, ref msg, ref cond, .. } => {
self.check_assertion(*expected, msg, cond, location);
}
TerminatorKind::SwitchInt { ref discr, ref targets } => {
if let Some(ref value) = self.eval_operand(&discr, location)
&& let Some(value_const) = self.use_ecx(location, |this| this.ecx.read_scalar(value))
&& let Ok(constant) = value_const.try_to_int()
&& let Ok(constant) = constant.to_bits(constant.size())
{
// We managed to evaluate the discriminant, so we know we only need to visit
// one target.
let target = targets.target_for_value(constant);
self.worklist.push(target);
return;
}
// We failed to evaluate the discriminant, fallback to visiting all successors.
}
// None of these have Operands to const-propagate.
TerminatorKind::Goto { .. }
| TerminatorKind::UnwindResume
| TerminatorKind::UnwindTerminate(_)
| TerminatorKind::Return
| TerminatorKind::Unreachable
| TerminatorKind::Drop { .. }
| TerminatorKind::Yield { .. }
| TerminatorKind::GeneratorDrop
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::Call { .. }
| TerminatorKind::InlineAsm { .. } => {}
}
self.worklist.extend(terminator.successors());
}
fn visit_basic_block_data(&mut self, block: BasicBlock, data: &BasicBlockData<'tcx>) {
self.super_basic_block_data(block, data);
// We remove all Locals which are restricted in propagation to their containing blocks and
// which were modified in the current block.
// Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
let mut written_only_inside_own_block_locals =
std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
// This loop can get very hot for some bodies: it check each local in each bb.
// To avoid this quadratic behaviour, we only clear the locals that were modified inside
// the current block.
for local in written_only_inside_own_block_locals.drain() {
debug_assert_eq!(
self.ecx.machine.can_const_prop[local],
ConstPropMode::OnlyInsideOwnBlock
);
Self::remove_const(&mut self.ecx, local);
}
self.ecx.machine.written_only_inside_own_block_locals =
written_only_inside_own_block_locals;
if cfg!(debug_assertions) {
for (local, &mode) in self.ecx.machine.can_const_prop.iter_enumerated() {
match mode {
ConstPropMode::FullConstProp => {}
ConstPropMode::NoPropagation | ConstPropMode::OnlyInsideOwnBlock => {
self.ensure_not_propagated(local);
}
}
}
}
}
}