diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/dataflow_const_prop.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/dataflow_const_prop.rs | 150 |
1 files changed, 122 insertions, 28 deletions
diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index c75fe2327..49ded10ba 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -5,6 +5,7 @@ use rustc_const_eval::const_eval::CheckAlignment; use rustc_const_eval::interpret::{ConstValue, ImmTy, Immediate, InterpCx, Scalar}; use rustc_data_structures::fx::FxHashMap; +use rustc_hir::def::DefKind; use rustc_middle::mir::visit::{MutVisitor, Visitor}; use rustc_middle::mir::*; use rustc_middle::ty::{self, Ty, TyCtxt}; @@ -12,6 +13,7 @@ use rustc_mir_dataflow::value_analysis::{Map, State, TrackElem, ValueAnalysis, V use rustc_mir_dataflow::{lattice::FlatSet, Analysis, ResultsVisitor, SwitchIntEdgeEffects}; use rustc_span::DUMMY_SP; use rustc_target::abi::Align; +use rustc_target::abi::VariantIdx; use crate::MirPass; @@ -29,14 +31,12 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp { #[instrument(skip_all level = "debug")] fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + debug!(def_id = ?body.source.def_id()); if tcx.sess.mir_opt_level() < 4 && body.basic_blocks.len() > BLOCK_LIMIT { debug!("aborted dataflow const prop due too many basic blocks"); return; } - // Decide which places to track during the analysis. - let map = Map::from_filter(tcx, body, Ty::is_scalar); - // We want to have a somewhat linear runtime w.r.t. the number of statements/terminators. // Let's call this number `n`. Dataflow analysis has `O(h*n)` transfer function // applications, where `h` is the height of the lattice. Because the height of our lattice @@ -45,10 +45,10 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp { // `O(num_nodes * tracked_places * n)` in terms of time complexity. Since the number of // map nodes is strongly correlated to the number of tracked places, this becomes more or // less `O(n)` if we place a constant limit on the number of tracked places. - if tcx.sess.mir_opt_level() < 4 && map.tracked_places() > PLACE_LIMIT { - debug!("aborted dataflow const prop due to too many tracked places"); - return; - } + let place_limit = if tcx.sess.mir_opt_level() < 4 { Some(PLACE_LIMIT) } else { None }; + + // Decide which places to track during the analysis. + let map = Map::from_filter(tcx, body, Ty::is_scalar, place_limit); // Perform the actual dataflow analysis. let analysis = ConstAnalysis::new(tcx, body, map); @@ -62,14 +62,31 @@ impl<'tcx> MirPass<'tcx> for DataflowConstProp { } } -struct ConstAnalysis<'tcx> { +struct ConstAnalysis<'a, 'tcx> { map: Map, tcx: TyCtxt<'tcx>, + local_decls: &'a LocalDecls<'tcx>, ecx: InterpCx<'tcx, 'tcx, DummyMachine>, param_env: ty::ParamEnv<'tcx>, } -impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> { +impl<'tcx> ConstAnalysis<'_, 'tcx> { + fn eval_discriminant( + &self, + enum_ty: Ty<'tcx>, + variant_index: VariantIdx, + ) -> Option<ScalarTy<'tcx>> { + if !enum_ty.is_enum() { + return None; + } + let discr = enum_ty.discriminant_for_variant(self.tcx, variant_index)?; + let discr_layout = self.tcx.layout_of(self.param_env.and(discr.ty)).ok()?; + let discr_value = Scalar::try_from_uint(discr.val, discr_layout.size)?; + Some(ScalarTy(discr_value, discr.ty)) + } +} + +impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> { type Value = FlatSet<ScalarTy<'tcx>>; const NAME: &'static str = "ConstAnalysis"; @@ -78,6 +95,25 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> { &self.map } + fn handle_statement(&self, statement: &Statement<'tcx>, state: &mut State<Self::Value>) { + match statement.kind { + StatementKind::SetDiscriminant { box ref place, variant_index } => { + state.flood_discr(place.as_ref(), &self.map); + if self.map.find_discr(place.as_ref()).is_some() { + let enum_ty = place.ty(self.local_decls, self.tcx).ty; + if let Some(discr) = self.eval_discriminant(enum_ty, variant_index) { + state.assign_discr( + place.as_ref(), + ValueOrPlace::Value(FlatSet::Elem(discr)), + &self.map, + ); + } + } + } + _ => self.super_statement(statement, state), + } + } + fn handle_assign( &self, target: Place<'tcx>, @@ -85,13 +121,59 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> { state: &mut State<Self::Value>, ) { match rvalue { + Rvalue::Aggregate(kind, operands) => { + // If we assign `target = Enum::Variant#0(operand)`, + // we must make sure that all `target as Variant#i` are `Top`. + state.flood(target.as_ref(), self.map()); + + if let Some(target_idx) = self.map().find(target.as_ref()) { + let (variant_target, variant_index) = match **kind { + AggregateKind::Tuple | AggregateKind::Closure(..) => { + (Some(target_idx), None) + } + AggregateKind::Adt(def_id, variant_index, ..) => { + match self.tcx.def_kind(def_id) { + DefKind::Struct => (Some(target_idx), None), + DefKind::Enum => ( + self.map.apply(target_idx, TrackElem::Variant(variant_index)), + Some(variant_index), + ), + _ => (None, None), + } + } + _ => (None, None), + }; + if let Some(variant_target_idx) = variant_target { + for (field_index, operand) in operands.iter().enumerate() { + if let Some(field) = self.map().apply( + variant_target_idx, + TrackElem::Field(Field::from_usize(field_index)), + ) { + let result = self.handle_operand(operand, state); + state.insert_idx(field, result, self.map()); + } + } + } + if let Some(variant_index) = variant_index + && let Some(discr_idx) = self.map().apply(target_idx, TrackElem::Discriminant) + { + // We are assigning the discriminant as part of an aggregate. + // This discriminant can only alias a variant field's value if the operand + // had an invalid value for that type. + // Using invalid values is UB, so we are allowed to perform the assignment + // without extra flooding. + let enum_ty = target.ty(self.local_decls, self.tcx).ty; + if let Some(discr_val) = self.eval_discriminant(enum_ty, variant_index) { + state.insert_value_idx(discr_idx, FlatSet::Elem(discr_val), &self.map); + } + } + } + } Rvalue::CheckedBinaryOp(op, box (left, right)) => { + // Flood everything now, so we can use `insert_value_idx` directly later. + state.flood(target.as_ref(), self.map()); + let target = self.map().find(target.as_ref()); - if let Some(target) = target { - // We should not track any projections other than - // what is overwritten below, but just in case... - state.flood_idx(target, self.map()); - } let value_target = target .and_then(|target| self.map().apply(target, TrackElem::Field(0_u32.into()))); @@ -102,26 +184,19 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> { let (val, overflow) = self.binary_op(state, *op, left, right); if let Some(value_target) = value_target { - state.assign_idx(value_target, ValueOrPlace::Value(val), self.map()); + // We have flooded `target` earlier. + state.insert_value_idx(value_target, val, self.map()); } if let Some(overflow_target) = overflow_target { let overflow = match overflow { FlatSet::Top => FlatSet::Top, FlatSet::Elem(overflow) => { - if overflow { - // Overflow cannot be reliably propagated. See: https://github.com/rust-lang/rust/pull/101168#issuecomment-1288091446 - FlatSet::Top - } else { - self.wrap_scalar(Scalar::from_bool(false), self.tcx.types.bool) - } + self.wrap_scalar(Scalar::from_bool(overflow), self.tcx.types.bool) } FlatSet::Bottom => FlatSet::Bottom, }; - state.assign_idx( - overflow_target, - ValueOrPlace::Value(overflow), - self.map(), - ); + // We have flooded `target` earlier. + state.insert_value_idx(overflow_target, overflow, self.map()); } } } @@ -170,6 +245,9 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'tcx> { FlatSet::Bottom => ValueOrPlace::Value(FlatSet::Bottom), FlatSet::Top => ValueOrPlace::Value(FlatSet::Top), }, + Rvalue::Discriminant(place) => { + ValueOrPlace::Value(state.get_discr(place.as_ref(), self.map())) + } _ => self.super_rvalue(rvalue, state), } } @@ -243,12 +321,13 @@ impl<'tcx> std::fmt::Debug for ScalarTy<'tcx> { } } -impl<'tcx> ConstAnalysis<'tcx> { - pub fn new(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, map: Map) -> Self { +impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> { + pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, map: Map) -> Self { let param_env = tcx.param_env(body.source.def_id()); Self { map, tcx, + local_decls: &body.local_decls, ecx: InterpCx::new(tcx, DUMMY_SP, param_env, DummyMachine), param_env: param_env, } @@ -441,6 +520,21 @@ impl<'tcx, 'map, 'a> Visitor<'tcx> for OperandCollector<'tcx, 'map, 'a> { _ => (), } } + + fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { + match rvalue { + Rvalue::Discriminant(place) => { + match self.state.get_discr(place.as_ref(), self.visitor.map) { + FlatSet::Top => (), + FlatSet::Elem(value) => { + self.visitor.before_effect.insert((location, *place), value); + } + FlatSet::Bottom => (), + } + } + _ => self.super_rvalue(rvalue, location), + } + } } struct DummyMachine; |