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JumpThreading: Bail out on interp errors

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clubby789 2024-10-07 17:31:43 +00:00
parent 9f35fe47c7
commit 41a5d8ef3d
1 changed files with 91 additions and 67 deletions
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152
compiler/rustc_mir_transform/src/jump_threading.rs
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@ -90,7 +90,11 @@ impl<'tcx> crate::MirPass<'tcx> for JumpThreading {
}; };
for bb in body.basic_blocks.indices() { for bb in body.basic_blocks.indices() {
finder.start_from_switch(bb); let old_len = finder.opportunities.len();
// If we have any const-eval errors discard any opportunities found
if finder.start_from_switch(bb).is_none() {
finder.opportunities.truncate(old_len);
}
} }
let opportunities = finder.opportunities; let opportunities = finder.opportunities;
@ -172,8 +176,21 @@ impl<'a> ConditionSet<'a> {
self.iter().filter(move |c| c.matches(value)) self.iter().filter(move |c| c.matches(value))
} }
fn map(self, arena: &'a DroplessArena, f: impl Fn(Condition) -> Condition) -> ConditionSet<'a> { fn map(
ConditionSet(arena.alloc_from_iter(self.iter().map(f))) self,
arena: &'a DroplessArena,
f: impl Fn(Condition) -> Option<Condition>,
) -> Option<ConditionSet<'a>> {
let mut all_ok = true;
let set = arena.alloc_from_iter(self.iter().map_while(|c| {
if let Some(c) = f(c) {
Some(c)
} else {
all_ok = false;
None
}
}));
all_ok.then_some(ConditionSet(set))
} }
} }
@ -184,28 +201,28 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
/// Recursion entry point to find threading opportunities. /// Recursion entry point to find threading opportunities.
#[instrument(level = "trace", skip(self))] #[instrument(level = "trace", skip(self))]
fn start_from_switch(&mut self, bb: BasicBlock) { fn start_from_switch(&mut self, bb: BasicBlock) -> Option<()> {
let bbdata = &self.body[bb]; let bbdata = &self.body[bb];
if bbdata.is_cleanup || self.loop_headers.contains(bb) { if bbdata.is_cleanup || self.loop_headers.contains(bb) {
return; return Some(());
} }
let Some((discr, targets)) = bbdata.terminator().kind.as_switch() else { return }; let Some((discr, targets)) = bbdata.terminator().kind.as_switch() else { return Some(()) };
let Some(discr) = discr.place() else { return }; let Some(discr) = discr.place() else { return Some(()) };
debug!(?discr, ?bb); debug!(?discr, ?bb);
let discr_ty = discr.ty(self.body, self.tcx).ty; let discr_ty = discr.ty(self.body, self.tcx).ty;
let Ok(discr_layout) = self.ecx.layout_of(discr_ty) else { let Ok(discr_layout) = self.ecx.layout_of(discr_ty) else {
return; return Some(());
}; };
let Some(discr) = self.map.find(discr.as_ref()) else { return }; let Some(discr) = self.map.find(discr.as_ref()) else { return Some(()) };
debug!(?discr); debug!(?discr);
let cost = CostChecker::new(self.tcx, self.typing_env, None, self.body); let cost = CostChecker::new(self.tcx, self.typing_env, None, self.body);
let mut state = State::new_reachable(); let mut state = State::new_reachable();
let conds = if let Some((value, then, else_)) = targets.as_static_if() { let conds = if let Some((value, then, else_)) = targets.as_static_if() {
let Some(value) = ScalarInt::try_from_uint(value, discr_layout.size) else { return }; let value = ScalarInt::try_from_uint(value, discr_layout.size)?;
self.arena.alloc_from_iter([ self.arena.alloc_from_iter([
Condition { value, polarity: Polarity::Eq, target: then }, Condition { value, polarity: Polarity::Eq, target: then },
Condition { value, polarity: Polarity::Ne, target: else_ }, Condition { value, polarity: Polarity::Ne, target: else_ },
@ -219,7 +236,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
let conds = ConditionSet(conds); let conds = ConditionSet(conds);
state.insert_value_idx(discr, conds, &self.map); state.insert_value_idx(discr, conds, &self.map);
self.find_opportunity(bb, state, cost, 0); self.find_opportunity(bb, state, cost, 0)
} }
/// Recursively walk statements backwards from this bb's terminator to find threading /// Recursively walk statements backwards from this bb's terminator to find threading
@ -231,10 +248,10 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
mut state: State<ConditionSet<'a>>, mut state: State<ConditionSet<'a>>,
mut cost: CostChecker<'_, 'tcx>, mut cost: CostChecker<'_, 'tcx>,
depth: usize, depth: usize,
) { ) -> Option<()> {
// Do not thread through loop headers. // Do not thread through loop headers.
if self.loop_headers.contains(bb) { if self.loop_headers.contains(bb) {
return; return Some(());
} }
debug!(cost = ?cost.cost()); debug!(cost = ?cost.cost());
@ -242,16 +259,16 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
self.body.basic_blocks[bb].statements.iter().enumerate().rev() self.body.basic_blocks[bb].statements.iter().enumerate().rev()
{ {
if self.is_empty(&state) { if self.is_empty(&state) {
return; return Some(());
} }
cost.visit_statement(stmt, Location { block: bb, statement_index }); cost.visit_statement(stmt, Location { block: bb, statement_index });
if cost.cost() > MAX_COST { if cost.cost() > MAX_COST {
return; return Some(());
} }
// Attempt to turn the `current_condition` on `lhs` into a condition on another place. // Attempt to turn the `current_condition` on `lhs` into a condition on another place.
self.process_statement(bb, stmt, &mut state); self.process_statement(bb, stmt, &mut state)?;
// When a statement mutates a place, assignments to that place that happen // When a statement mutates a place, assignments to that place that happen
// above the mutation cannot fulfill a condition. // above the mutation cannot fulfill a condition.
@ -263,7 +280,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
} }
if self.is_empty(&state) || depth >= MAX_BACKTRACK { if self.is_empty(&state) || depth >= MAX_BACKTRACK {
return; return Some(());
} }
let last_non_rec = self.opportunities.len(); let last_non_rec = self.opportunities.len();
@ -276,9 +293,9 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
match term.kind { match term.kind {
TerminatorKind::SwitchInt { ref discr, ref targets } => { TerminatorKind::SwitchInt { ref discr, ref targets } => {
self.process_switch_int(discr, targets, bb, &mut state); self.process_switch_int(discr, targets, bb, &mut state);
self.find_opportunity(pred, state, cost, depth + 1); self.find_opportunity(pred, state, cost, depth + 1)?;
} }
_ => self.recurse_through_terminator(pred, || state, &cost, depth), _ => self.recurse_through_terminator(pred, || state, &cost, depth)?,
} }
} else if let &[ref predecessors @ .., last_pred] = &predecessors[..] { } else if let &[ref predecessors @ .., last_pred] = &predecessors[..] {
for &pred in predecessors { for &pred in predecessors {
@ -303,12 +320,13 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
let first = &mut new_tos[0]; let first = &mut new_tos[0];
*first = ThreadingOpportunity { chain: vec![bb], target: first.target }; *first = ThreadingOpportunity { chain: vec![bb], target: first.target };
self.opportunities.truncate(last_non_rec + 1); self.opportunities.truncate(last_non_rec + 1);
return; return Some(());
} }
for op in self.opportunities[last_non_rec..].iter_mut() { for op in self.opportunities[last_non_rec..].iter_mut() {
op.chain.push(bb); op.chain.push(bb);
} }
Some(())
} }
/// Extract the mutated place from a statement. /// Extract the mutated place from a statement.
@ -422,23 +440,23 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
lhs: PlaceIndex, lhs: PlaceIndex,
rhs: &Operand<'tcx>, rhs: &Operand<'tcx>,
state: &mut State<ConditionSet<'a>>, state: &mut State<ConditionSet<'a>>,
) { ) -> Option<()> {
match rhs { match rhs {
// If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`. // If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`.
Operand::Constant(constant) => { Operand::Constant(constant) => {
let Some(constant) = let constant = self
self.ecx.eval_mir_constant(&constant.const_, constant.span, None).discard_err() .ecx
else { .eval_mir_constant(&constant.const_, constant.span, None)
return; .discard_err()?;
};
self.process_constant(bb, lhs, constant, state); self.process_constant(bb, lhs, constant, state);
} }
// Transfer the conditions on the copied rhs. // Transfer the conditions on the copied rhs.
Operand::Move(rhs) | Operand::Copy(rhs) => { Operand::Move(rhs) | Operand::Copy(rhs) => {
let Some(rhs) = self.map.find(rhs.as_ref()) else { return }; let Some(rhs) = self.map.find(rhs.as_ref()) else { return Some(()) };
state.insert_place_idx(rhs, lhs, &self.map); state.insert_place_idx(rhs, lhs, &self.map);
} }
} }
Some(())
} }
#[instrument(level = "trace", skip(self))] #[instrument(level = "trace", skip(self))]
@ -448,14 +466,18 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
lhs_place: &Place<'tcx>, lhs_place: &Place<'tcx>,
rhs: &Rvalue<'tcx>, rhs: &Rvalue<'tcx>,
state: &mut State<ConditionSet<'a>>, state: &mut State<ConditionSet<'a>>,
) { ) -> Option<()> {
let Some(lhs) = self.map.find(lhs_place.as_ref()) else { return }; let Some(lhs) = self.map.find(lhs_place.as_ref()) else {
return Some(());
};
match rhs { match rhs {
Rvalue::Use(operand) => self.process_operand(bb, lhs, operand, state), Rvalue::Use(operand) => self.process_operand(bb, lhs, operand, state)?,
// Transfer the conditions on the copy rhs. // Transfer the conditions on the copy rhs.
Rvalue::CopyForDeref(rhs) => self.process_operand(bb, lhs, &Operand::Copy(*rhs), state), Rvalue::CopyForDeref(rhs) => {
self.process_operand(bb, lhs, &Operand::Copy(*rhs), state)?
}
Rvalue::Discriminant(rhs) => { Rvalue::Discriminant(rhs) => {
let Some(rhs) = self.map.find_discr(rhs.as_ref()) else { return }; let Some(rhs) = self.map.find_discr(rhs.as_ref()) else { return Some(()) };
state.insert_place_idx(rhs, lhs, &self.map); state.insert_place_idx(rhs, lhs, &self.map);
} }
// If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`. // If we expect `lhs ?= A`, we have an opportunity if we assume `constant == A`.
@ -463,7 +485,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
let agg_ty = lhs_place.ty(self.body, self.tcx).ty; let agg_ty = lhs_place.ty(self.body, self.tcx).ty;
let lhs = match kind { let lhs = match kind {
// Do not support unions. // Do not support unions.
AggregateKind::Adt(.., Some(_)) => return, AggregateKind::Adt(.., Some(_)) => return Some(()),
AggregateKind::Adt(_, variant_index, ..) if agg_ty.is_enum() => { AggregateKind::Adt(_, variant_index, ..) if agg_ty.is_enum() => {
if let Some(discr_target) = self.map.apply(lhs, TrackElem::Discriminant) if let Some(discr_target) = self.map.apply(lhs, TrackElem::Discriminant)
&& let Some(discr_value) = self && let Some(discr_value) = self
@ -476,31 +498,31 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
if let Some(idx) = self.map.apply(lhs, TrackElem::Variant(*variant_index)) { if let Some(idx) = self.map.apply(lhs, TrackElem::Variant(*variant_index)) {
idx idx
} else { } else {
return; return Some(());
} }
} }
_ => lhs, _ => lhs,
}; };
for (field_index, operand) in operands.iter_enumerated() { for (field_index, operand) in operands.iter_enumerated() {
if let Some(field) = self.map.apply(lhs, TrackElem::Field(field_index)) { if let Some(field) = self.map.apply(lhs, TrackElem::Field(field_index)) {
self.process_operand(bb, field, operand, state); self.process_operand(bb, field, operand, state)?;
} }
} }
} }
// Transfer the conditions on the copy rhs, after inverting the value of the condition. // Transfer the conditions on the copy rhs, after inverting the value of the condition.
Rvalue::UnaryOp(UnOp::Not, Operand::Move(place) | Operand::Copy(place)) => { Rvalue::UnaryOp(UnOp::Not, Operand::Move(place) | Operand::Copy(place)) => {
let layout = self.ecx.layout_of(place.ty(self.body, self.tcx).ty).unwrap(); let layout = self.ecx.layout_of(place.ty(self.body, self.tcx).ty).unwrap();
let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return }; let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return Some(()) };
let Some(place) = self.map.find(place.as_ref()) else { return }; let Some(place) = self.map.find(place.as_ref()) else { return Some(()) };
let conds = conditions.map(self.arena, |mut cond| { let conds = conditions.map(self.arena, |mut cond| {
cond.value = self cond.value = self
.ecx .ecx
.unary_op(UnOp::Not, &ImmTy::from_scalar_int(cond.value, layout)) .unary_op(UnOp::Not, &ImmTy::from_scalar_int(cond.value, layout))
.unwrap() .discard_err()?
.to_scalar_int() .to_scalar_int()
.unwrap(); .discard_err()?;
cond Some(cond)
}); })?;
state.insert_value_idx(place, conds, &self.map); state.insert_value_idx(place, conds, &self.map);
} }
// We expect `lhs ?= A`. We found `lhs = Eq(rhs, B)`. // We expect `lhs ?= A`. We found `lhs = Eq(rhs, B)`.
@ -510,34 +532,34 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
box (Operand::Move(place) | Operand::Copy(place), Operand::Constant(value)) box (Operand::Move(place) | Operand::Copy(place), Operand::Constant(value))
| box (Operand::Constant(value), Operand::Move(place) | Operand::Copy(place)), | box (Operand::Constant(value), Operand::Move(place) | Operand::Copy(place)),
) => { ) => {
let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return }; let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return Some(()) };
let Some(place) = self.map.find(place.as_ref()) else { return }; let Some(place) = self.map.find(place.as_ref()) else { return Some(()) };
let equals = match op { let equals = match op {
BinOp::Eq => ScalarInt::TRUE, BinOp::Eq => ScalarInt::TRUE,
BinOp::Ne => ScalarInt::FALSE, BinOp::Ne => ScalarInt::FALSE,
_ => return, _ => return Some(()),
}; };
if value.const_.ty().is_floating_point() { if value.const_.ty().is_floating_point() {
// Floating point equality does not follow bit-patterns. // Floating point equality does not follow bit-patterns.
// -0.0 and NaN both have special rules for equality, // -0.0 and NaN both have special rules for equality,
// and therefore we cannot use integer comparisons for them. // and therefore we cannot use integer comparisons for them.
// Avoid handling them, though this could be extended in the future. // Avoid handling them, though this could be extended in the future.
return; return Some(());
} }
let Some(value) = value.const_.try_eval_scalar_int(self.tcx, self.typing_env) let value = value.const_.try_eval_scalar_int(self.tcx, self.typing_env)?;
else { let conds = conditions.map(self.arena, |c| {
return; Some(Condition {
};
let conds = conditions.map(self.arena, |c| Condition {
value, value,
polarity: if c.matches(equals) { Polarity::Eq } else { Polarity::Ne }, polarity: if c.matches(equals) { Polarity::Eq } else { Polarity::Ne },
..c ..c
}); })
})?;
state.insert_value_idx(place, conds, &self.map); state.insert_value_idx(place, conds, &self.map);
} }
_ => {} _ => {}
} }
Some(())
} }
#[instrument(level = "trace", skip(self))] #[instrument(level = "trace", skip(self))]
@ -546,7 +568,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
bb: BasicBlock, bb: BasicBlock,
stmt: &Statement<'tcx>, stmt: &Statement<'tcx>,
state: &mut State<ConditionSet<'a>>, state: &mut State<ConditionSet<'a>>,
) { ) -> Option<()> {
let register_opportunity = |c: Condition| { let register_opportunity = |c: Condition| {
debug!(?bb, ?c.target, "register"); debug!(?bb, ?c.target, "register");
self.opportunities.push(ThreadingOpportunity { chain: vec![bb], target: c.target }) self.opportunities.push(ThreadingOpportunity { chain: vec![bb], target: c.target })
@ -559,30 +581,32 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
// If we expect `discriminant(place) ?= A`, // If we expect `discriminant(place) ?= A`,
// we have an opportunity if `variant_index ?= A`. // we have an opportunity if `variant_index ?= A`.
StatementKind::SetDiscriminant { box place, variant_index } => { StatementKind::SetDiscriminant { box place, variant_index } => {
let Some(discr_target) = self.map.find_discr(place.as_ref()) else { return }; let Some(discr_target) = self.map.find_discr(place.as_ref()) else {
return Some(());
};
let enum_ty = place.ty(self.body, self.tcx).ty; let enum_ty = place.ty(self.body, self.tcx).ty;
// `SetDiscriminant` guarantees that the discriminant is now `variant_index`. // `SetDiscriminant` guarantees that the discriminant is now `variant_index`.
// Even if the discriminant write does nothing due to niches, it is UB to set the // Even if the discriminant write does nothing due to niches, it is UB to set the
// discriminant when the data does not encode the desired discriminant. // discriminant when the data does not encode the desired discriminant.
let Some(discr) = let discr =
self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err() self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()?;
else {
return;
};
self.process_immediate(bb, discr_target, discr, state); self.process_immediate(bb, discr_target, discr, state);
} }
// If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`. // If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`.
StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume( StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(
Operand::Copy(place) | Operand::Move(place), Operand::Copy(place) | Operand::Move(place),
)) => { )) => {
let Some(conditions) = state.try_get(place.as_ref(), &self.map) else { return }; let Some(conditions) = state.try_get(place.as_ref(), &self.map) else {
return Some(());
};
conditions.iter_matches(ScalarInt::TRUE).for_each(register_opportunity); conditions.iter_matches(ScalarInt::TRUE).for_each(register_opportunity);
} }
StatementKind::Assign(box (lhs_place, rhs)) => { StatementKind::Assign(box (lhs_place, rhs)) => {
self.process_assign(bb, lhs_place, rhs, state); self.process_assign(bb, lhs_place, rhs, state)?;
} }
_ => {} _ => {}
} }
Some(())
} }
#[instrument(level = "trace", skip(self, state, cost))] #[instrument(level = "trace", skip(self, state, cost))]
@ -593,7 +617,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
state: impl FnOnce() -> State<ConditionSet<'a>>, state: impl FnOnce() -> State<ConditionSet<'a>>,
cost: &CostChecker<'_, 'tcx>, cost: &CostChecker<'_, 'tcx>,
depth: usize, depth: usize,
) { ) -> Option<()> {
let term = self.body.basic_blocks[bb].terminator(); let term = self.body.basic_blocks[bb].terminator();
let place_to_flood = match term.kind { let place_to_flood = match term.kind {
// We come from a target, so those are not possible. // We come from a target, so those are not possible.
@ -608,9 +632,9 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
| TerminatorKind::FalseUnwind { .. } | TerminatorKind::FalseUnwind { .. }
| TerminatorKind::Yield { .. } => bug!("{term:?} invalid"), | TerminatorKind::Yield { .. } => bug!("{term:?} invalid"),
// Cannot reason about inline asm. // Cannot reason about inline asm.
TerminatorKind::InlineAsm { .. } => return, TerminatorKind::InlineAsm { .. } => return Some(()),
// `SwitchInt` is handled specially. // `SwitchInt` is handled specially.
TerminatorKind::SwitchInt { .. } => return, TerminatorKind::SwitchInt { .. } => return Some(()),
// We can recurse, no thing particular to do. // We can recurse, no thing particular to do.
TerminatorKind::Goto { .. } => None, TerminatorKind::Goto { .. } => None,
// Flood the overwritten place, and progress through. // Flood the overwritten place, and progress through.
@ -625,7 +649,7 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
if let Some(place_to_flood) = place_to_flood { if let Some(place_to_flood) = place_to_flood {
state.flood_with(place_to_flood.as_ref(), &self.map, ConditionSet::BOTTOM); state.flood_with(place_to_flood.as_ref(), &self.map, ConditionSet::BOTTOM);
} }
self.find_opportunity(bb, state, cost.clone(), depth + 1); self.find_opportunity(bb, state, cost.clone(), depth + 1)
} }
#[instrument(level = "trace", skip(self))] #[instrument(level = "trace", skip(self))]