Remove `ValueAnalysis` and `ValueAnalysisWrapper`.

They represent a lot of abstraction and indirection, but they're only
used for `ConstAnalysis`, and apparently won't be used for any other
analyses in the future. This commit inlines and removes them, which
makes `ConstAnalysis` easier to read and understand.

1 files changed, 274 insertions, 59 deletions

diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index c084b20772f..b8e35587b87 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -2,6 +2,9 @@
 //!
 //! Currently, this pass only propagates scalar values.
 
+use std::assert_matches::assert_matches;
+use std::fmt::Formatter;
+
 use rustc_abi::{BackendRepr, FIRST_VARIANT, FieldIdx, Size, VariantIdx};
 use rustc_const_eval::const_eval::{DummyMachine, throw_machine_stop_str};
 use rustc_const_eval::interpret::{
@@ -15,9 +18,10 @@ use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::{HasParamEnv, LayoutOf};
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_mir_dataflow::lattice::FlatSet;
+use rustc_mir_dataflow::fmt::DebugWithContext;
+use rustc_mir_dataflow::lattice::{FlatSet, HasBottom};
 use rustc_mir_dataflow::value_analysis::{
-    Map, PlaceIndex, State, TrackElem, ValueAnalysis, ValueAnalysisWrapper, ValueOrPlace,
+    Map, PlaceIndex, State, TrackElem, ValueOrPlace, debug_with_context,
 };
 use rustc_mir_dataflow::{Analysis, Results, ResultsVisitor};
 use rustc_span::DUMMY_SP;
@@ -58,8 +62,8 @@ impl<'tcx> crate::MirPass<'tcx> for DataflowConstProp {
 
         // Perform the actual dataflow analysis.
         let analysis = ConstAnalysis::new(tcx, body, map);
-        let mut results = debug_span!("analyze")
-            .in_scope(|| analysis.wrap().iterate_to_fixpoint(tcx, body, None));
+        let mut results =
+            debug_span!("analyze").in_scope(|| analysis.iterate_to_fixpoint(tcx, body, None));
 
         // Collect results and patch the body afterwards.
         let mut visitor = Collector::new(tcx, &body.local_decls);
@@ -69,6 +73,10 @@ impl<'tcx> crate::MirPass<'tcx> for DataflowConstProp {
     }
 }
 
+// Note: Currently, places that have their reference taken cannot be tracked. Although this would
+// be possible, it has to rely on some aliasing model, which we are not ready to commit to yet.
+// Because of that, we can assume that the only way to change the value behind a tracked place is
+// by direct assignment.
 struct ConstAnalysis<'a, 'tcx> {
     map: Map<'tcx>,
     tcx: TyCtxt<'tcx>,
@@ -77,20 +85,198 @@ struct ConstAnalysis<'a, 'tcx> {
     param_env: ty::ParamEnv<'tcx>,
 }
 
-impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
-    type Value = FlatSet<Scalar>;
+impl<'tcx> Analysis<'tcx> for ConstAnalysis<'_, 'tcx> {
+    type Domain = State<FlatSet<Scalar>>;
 
     const NAME: &'static str = "ConstAnalysis";
 
-    fn map(&self) -> &Map<'tcx> {
-        &self.map
+    // The bottom state denotes uninitialized memory. Because we are only doing a sound
+    // approximation of the actual execution, we can also use this state for places where access
+    // would be UB.
+    fn bottom_value(&self, _body: &Body<'tcx>) -> Self::Domain {
+        State::Unreachable
+    }
+
+    fn initialize_start_block(&self, body: &Body<'tcx>, state: &mut Self::Domain) {
+        // The initial state maps all tracked places of argument projections to ⊤ and the rest to ⊥.
+        assert_matches!(state, State::Unreachable);
+        *state = State::new_reachable();
+        for arg in body.args_iter() {
+            state.flood(PlaceRef { local: arg, projection: &[] }, &self.map);
+        }
+    }
+
+    fn apply_statement_effect(
+        &mut self,
+        state: &mut Self::Domain,
+        statement: &Statement<'tcx>,
+        _location: Location,
+    ) {
+        if state.is_reachable() {
+            self.handle_statement(statement, state);
+        }
+    }
+
+    fn apply_terminator_effect<'mir>(
+        &mut self,
+        state: &mut Self::Domain,
+        terminator: &'mir Terminator<'tcx>,
+        _location: Location,
+    ) -> TerminatorEdges<'mir, 'tcx> {
+        if state.is_reachable() {
+            self.handle_terminator(terminator, state)
+        } else {
+            TerminatorEdges::None
+        }
+    }
+
+    fn apply_call_return_effect(
+        &mut self,
+        state: &mut Self::Domain,
+        _block: BasicBlock,
+        return_places: CallReturnPlaces<'_, 'tcx>,
+    ) {
+        if state.is_reachable() {
+            self.handle_call_return(return_places, state)
+        }
+    }
+}
+
+impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
+    fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, map: Map<'tcx>) -> Self {
+        let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
+        Self {
+            map,
+            tcx,
+            local_decls: &body.local_decls,
+            ecx: InterpCx::new(tcx, DUMMY_SP, param_env, DummyMachine),
+            param_env,
+        }
+    }
+
+    fn handle_statement(&self, statement: &Statement<'tcx>, state: &mut State<FlatSet<Scalar>>) {
+        match &statement.kind {
+            StatementKind::Assign(box (place, rvalue)) => {
+                self.handle_assign(*place, rvalue, state);
+            }
+            StatementKind::SetDiscriminant { box place, variant_index } => {
+                self.handle_set_discriminant(*place, *variant_index, state);
+            }
+            StatementKind::Intrinsic(box intrinsic) => {
+                self.handle_intrinsic(intrinsic);
+            }
+            StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => {
+                // StorageLive leaves the local in an uninitialized state.
+                // StorageDead makes it UB to access the local afterwards.
+                state.flood_with(
+                    Place::from(*local).as_ref(),
+                    &self.map,
+                    FlatSet::<Scalar>::BOTTOM,
+                );
+            }
+            StatementKind::Deinit(box place) => {
+                // Deinit makes the place uninitialized.
+                state.flood_with(place.as_ref(), &self.map, FlatSet::<Scalar>::BOTTOM);
+            }
+            StatementKind::Retag(..) => {
+                // We don't track references.
+            }
+            StatementKind::ConstEvalCounter
+            | StatementKind::Nop
+            | StatementKind::FakeRead(..)
+            | StatementKind::PlaceMention(..)
+            | StatementKind::Coverage(..)
+            | StatementKind::AscribeUserType(..) => (),
+        }
+    }
+
+    fn handle_intrinsic(&self, intrinsic: &NonDivergingIntrinsic<'tcx>) {
+        match intrinsic {
+            NonDivergingIntrinsic::Assume(..) => {
+                // Could use this, but ignoring it is sound.
+            }
+            NonDivergingIntrinsic::CopyNonOverlapping(CopyNonOverlapping {
+                dst: _,
+                src: _,
+                count: _,
+            }) => {
+                // This statement represents `*dst = *src`, `count` times.
+            }
+        }
+    }
+
+    fn handle_operand(
+        &self,
+        operand: &Operand<'tcx>,
+        state: &mut State<FlatSet<Scalar>>,
+    ) -> ValueOrPlace<FlatSet<Scalar>> {
+        match operand {
+            Operand::Constant(box constant) => {
+                ValueOrPlace::Value(self.handle_constant(constant, state))
+            }
+            Operand::Copy(place) | Operand::Move(place) => {
+                // On move, we would ideally flood the place with bottom. But with the current
+                // framework this is not possible (similar to `InterpCx::eval_operand`).
+                self.map.find(place.as_ref()).map(ValueOrPlace::Place).unwrap_or(ValueOrPlace::TOP)
+            }
+        }
+    }
+
+    /// The effect of a successful function call return should not be
+    /// applied here, see [`Analysis::apply_terminator_effect`].
+    fn handle_terminator<'mir>(
+        &self,
+        terminator: &'mir Terminator<'tcx>,
+        state: &mut State<FlatSet<Scalar>>,
+    ) -> TerminatorEdges<'mir, 'tcx> {
+        match &terminator.kind {
+            TerminatorKind::Call { .. } | TerminatorKind::InlineAsm { .. } => {
+                // Effect is applied by `handle_call_return`.
+            }
+            TerminatorKind::Drop { place, .. } => {
+                state.flood_with(place.as_ref(), &self.map, FlatSet::<Scalar>::BOTTOM);
+            }
+            TerminatorKind::Yield { .. } => {
+                // They would have an effect, but are not allowed in this phase.
+                bug!("encountered disallowed terminator");
+            }
+            TerminatorKind::SwitchInt { discr, targets } => {
+                return self.handle_switch_int(discr, targets, state);
+            }
+            TerminatorKind::TailCall { .. } => {
+                // FIXME(explicit_tail_calls): determine if we need to do something here (probably
+                // not)
+            }
+            TerminatorKind::Goto { .. }
+            | TerminatorKind::UnwindResume
+            | TerminatorKind::UnwindTerminate(_)
+            | TerminatorKind::Return
+            | TerminatorKind::Unreachable
+            | TerminatorKind::Assert { .. }
+            | TerminatorKind::CoroutineDrop
+            | TerminatorKind::FalseEdge { .. }
+            | TerminatorKind::FalseUnwind { .. } => {
+                // These terminators have no effect on the analysis.
+            }
+        }
+        terminator.edges()
+    }
+
+    fn handle_call_return(
+        &self,
+        return_places: CallReturnPlaces<'_, 'tcx>,
+        state: &mut State<FlatSet<Scalar>>,
+    ) {
+        return_places.for_each(|place| {
+            state.flood(place.as_ref(), &self.map);
+        })
     }
 
     fn handle_set_discriminant(
         &self,
         place: Place<'tcx>,
         variant_index: VariantIdx,
-        state: &mut State<Self::Value>,
+        state: &mut State<FlatSet<Scalar>>,
     ) {
         state.flood_discr(place.as_ref(), &self.map);
         if self.map.find_discr(place.as_ref()).is_some() {
@@ -109,17 +295,17 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
         &self,
         target: Place<'tcx>,
         rvalue: &Rvalue<'tcx>,
-        state: &mut State<Self::Value>,
+        state: &mut State<FlatSet<Scalar>>,
     ) {
         match rvalue {
             Rvalue::Use(operand) => {
-                state.flood(target.as_ref(), self.map());
+                state.flood(target.as_ref(), &self.map);
                 if let Some(target) = self.map.find(target.as_ref()) {
                     self.assign_operand(state, target, operand);
                 }
             }
             Rvalue::CopyForDeref(rhs) => {
-                state.flood(target.as_ref(), self.map());
+                state.flood(target.as_ref(), &self.map);
                 if let Some(target) = self.map.find(target.as_ref()) {
                     self.assign_operand(state, target, &Operand::Copy(*rhs));
                 }
@@ -127,9 +313,9 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
             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());
+                state.flood(target.as_ref(), &self.map);
 
-                let Some(target_idx) = self.map().find(target.as_ref()) else { return };
+                let Some(target_idx) = self.map.find(target.as_ref()) else { return };
 
                 let (variant_target, variant_index) = match **kind {
                     AggregateKind::Tuple | AggregateKind::Closure(..) => (Some(target_idx), None),
@@ -148,14 +334,14 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                 if let Some(variant_target_idx) = variant_target {
                     for (field_index, operand) in operands.iter_enumerated() {
                         if let Some(field) =
-                            self.map().apply(variant_target_idx, TrackElem::Field(field_index))
+                            self.map.apply(variant_target_idx, TrackElem::Field(field_index))
                         {
                             self.assign_operand(state, field, operand);
                         }
                     }
                 }
                 if let Some(variant_index) = variant_index
-                    && let Some(discr_idx) = self.map().apply(target_idx, TrackElem::Discriminant)
+                    && 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
@@ -170,23 +356,23 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
             }
             Rvalue::BinaryOp(op, box (left, right)) if op.is_overflowing() => {
                 // Flood everything now, so we can use `insert_value_idx` directly later.
-                state.flood(target.as_ref(), self.map());
+                state.flood(target.as_ref(), &self.map);
 
-                let Some(target) = self.map().find(target.as_ref()) else { return };
+                let Some(target) = self.map.find(target.as_ref()) else { return };
 
-                let value_target = self.map().apply(target, TrackElem::Field(0_u32.into()));
-                let overflow_target = self.map().apply(target, TrackElem::Field(1_u32.into()));
+                let value_target = self.map.apply(target, TrackElem::Field(0_u32.into()));
+                let overflow_target = self.map.apply(target, TrackElem::Field(1_u32.into()));
 
                 if value_target.is_some() || overflow_target.is_some() {
                     let (val, overflow) = self.binary_op(state, *op, left, right);
 
                     if let Some(value_target) = value_target {
                         // We have flooded `target` earlier.
-                        state.insert_value_idx(value_target, val, self.map());
+                        state.insert_value_idx(value_target, val, &self.map);
                     }
                     if let Some(overflow_target) = overflow_target {
                         // We have flooded `target` earlier.
-                        state.insert_value_idx(overflow_target, overflow, self.map());
+                        state.insert_value_idx(overflow_target, overflow, &self.map);
                     }
                 }
             }
@@ -196,27 +382,30 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                 _,
             ) => {
                 let pointer = self.handle_operand(operand, state);
-                state.assign(target.as_ref(), pointer, self.map());
+                state.assign(target.as_ref(), pointer, &self.map);
 
-                if let Some(target_len) = self.map().find_len(target.as_ref())
+                if let Some(target_len) = self.map.find_len(target.as_ref())
                     && let operand_ty = operand.ty(self.local_decls, self.tcx)
                     && let Some(operand_ty) = operand_ty.builtin_deref(true)
                     && let ty::Array(_, len) = operand_ty.kind()
                     && let Some(len) = Const::Ty(self.tcx.types.usize, *len)
                         .try_eval_scalar_int(self.tcx, self.param_env)
                 {
-                    state.insert_value_idx(target_len, FlatSet::Elem(len.into()), self.map());
+                    state.insert_value_idx(target_len, FlatSet::Elem(len.into()), &self.map);
                 }
             }
-            _ => self.super_assign(target, rvalue, state),
+            _ => {
+                let result = self.handle_rvalue(rvalue, state);
+                state.assign(target.as_ref(), result, &self.map);
+            }
         }
     }
 
     fn handle_rvalue(
         &self,
         rvalue: &Rvalue<'tcx>,
-        state: &mut State<Self::Value>,
-    ) -> ValueOrPlace<Self::Value> {
+        state: &mut State<FlatSet<Scalar>>,
+    ) -> ValueOrPlace<FlatSet<Scalar>> {
         let val = match rvalue {
             Rvalue::Len(place) => {
                 let place_ty = place.ty(self.local_decls, self.tcx);
@@ -225,7 +414,7 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                         .try_eval_scalar(self.tcx, self.param_env)
                         .map_or(FlatSet::Top, FlatSet::Elem)
                 } else if let [ProjectionElem::Deref] = place.projection[..] {
-                    state.get_len(place.local.into(), self.map())
+                    state.get_len(place.local.into(), &self.map)
                 } else {
                     FlatSet::Top
                 }
@@ -296,8 +485,24 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                 };
                 FlatSet::Elem(Scalar::from_target_usize(val, &self.tcx))
             }
-            Rvalue::Discriminant(place) => state.get_discr(place.as_ref(), self.map()),
-            _ => return self.super_rvalue(rvalue, state),
+            Rvalue::Discriminant(place) => state.get_discr(place.as_ref(), &self.map),
+            Rvalue::Use(operand) => return self.handle_operand(operand, state),
+            Rvalue::CopyForDeref(place) => {
+                return self.handle_operand(&Operand::Copy(*place), state);
+            }
+            Rvalue::Ref(..) | Rvalue::RawPtr(..) => {
+                // We don't track such places.
+                return ValueOrPlace::TOP;
+            }
+            Rvalue::Repeat(..)
+            | Rvalue::ThreadLocalRef(..)
+            | Rvalue::Cast(..)
+            | Rvalue::BinaryOp(..)
+            | Rvalue::Aggregate(..)
+            | Rvalue::ShallowInitBox(..) => {
+                // No modification is possible through these r-values.
+                return ValueOrPlace::TOP;
+            }
         };
         ValueOrPlace::Value(val)
     }
@@ -305,8 +510,8 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
     fn handle_constant(
         &self,
         constant: &ConstOperand<'tcx>,
-        _state: &mut State<Self::Value>,
-    ) -> Self::Value {
+        _state: &mut State<FlatSet<Scalar>>,
+    ) -> FlatSet<Scalar> {
         constant
             .const_
             .try_eval_scalar(self.tcx, self.param_env)
@@ -317,11 +522,11 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
         &self,
         discr: &'mir Operand<'tcx>,
         targets: &'mir SwitchTargets,
-        state: &mut State<Self::Value>,
+        state: &mut State<FlatSet<Scalar>>,
     ) -> TerminatorEdges<'mir, 'tcx> {
         let value = match self.handle_operand(discr, state) {
             ValueOrPlace::Value(value) => value,
-            ValueOrPlace::Place(place) => state.get_idx(place, self.map()),
+            ValueOrPlace::Place(place) => state.get_idx(place, &self.map),
         };
         match value {
             // We are branching on uninitialized data, this is UB, treat it as unreachable.
@@ -334,19 +539,6 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
             FlatSet::Top => TerminatorEdges::SwitchInt { discr, targets },
         }
     }
-}
-
-impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
-    fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, map: Map<'tcx>) -> Self {
-        let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
-        Self {
-            map,
-            tcx,
-            local_decls: &body.local_decls,
-            ecx: InterpCx::new(tcx, DUMMY_SP, param_env, DummyMachine),
-            param_env,
-        }
-    }
 
     /// The caller must have flooded `place`.
     fn assign_operand(
@@ -537,6 +729,30 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> {
     }
 }
 
+/// This is used to visualize the dataflow analysis.
+impl<'tcx> DebugWithContext<ConstAnalysis<'_, 'tcx>> for State<FlatSet<Scalar>> {
+    fn fmt_with(&self, ctxt: &ConstAnalysis<'_, 'tcx>, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            State::Reachable(values) => debug_with_context(values, None, &ctxt.map, f),
+            State::Unreachable => write!(f, "unreachable"),
+        }
+    }
+
+    fn fmt_diff_with(
+        &self,
+        old: &Self,
+        ctxt: &ConstAnalysis<'_, 'tcx>,
+        f: &mut Formatter<'_>,
+    ) -> std::fmt::Result {
+        match (self, old) {
+            (State::Reachable(this), State::Reachable(old)) => {
+                debug_with_context(this, Some(old), &ctxt.map, f)
+            }
+            _ => Ok(()), // Consider printing something here.
+        }
+    }
+}
+
 pub(crate) struct Patch<'tcx> {
     tcx: TyCtxt<'tcx>,
 
@@ -725,8 +941,7 @@ fn try_write_constant<'tcx>(
     interp_ok(())
 }
 
-impl<'mir, 'tcx>
-    ResultsVisitor<'mir, 'tcx, Results<'tcx, ValueAnalysisWrapper<ConstAnalysis<'_, 'tcx>>>>
+impl<'mir, 'tcx> ResultsVisitor<'mir, 'tcx, Results<'tcx, ConstAnalysis<'_, 'tcx>>>
     for Collector<'_, 'tcx>
 {
     type Domain = State<FlatSet<Scalar>>;
@@ -734,7 +949,7 @@ impl<'mir, 'tcx>
     #[instrument(level = "trace", skip(self, results, statement))]
     fn visit_statement_before_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, ValueAnalysisWrapper<ConstAnalysis<'_, 'tcx>>>,
+        results: &mut Results<'tcx, ConstAnalysis<'_, 'tcx>>,
         state: &Self::Domain,
         statement: &'mir Statement<'tcx>,
         location: Location,
@@ -744,8 +959,8 @@ impl<'mir, 'tcx>
                 OperandCollector {
                     state,
                     visitor: self,
-                    ecx: &mut results.analysis.0.ecx,
-                    map: &results.analysis.0.map,
+                    ecx: &mut results.analysis.ecx,
+                    map: &results.analysis.map,
                 }
                 .visit_rvalue(rvalue, location);
             }
@@ -756,7 +971,7 @@ impl<'mir, 'tcx>
     #[instrument(level = "trace", skip(self, results, statement))]
     fn visit_statement_after_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, ValueAnalysisWrapper<ConstAnalysis<'_, 'tcx>>>,
+        results: &mut Results<'tcx, ConstAnalysis<'_, 'tcx>>,
         state: &Self::Domain,
         statement: &'mir Statement<'tcx>,
         location: Location,
@@ -767,10 +982,10 @@ impl<'mir, 'tcx>
             }
             StatementKind::Assign(box (place, _)) => {
                 if let Some(value) = self.try_make_constant(
-                    &mut results.analysis.0.ecx,
+                    &mut results.analysis.ecx,
                     place,
                     state,
-                    &results.analysis.0.map,
+                    &results.analysis.map,
                 ) {
                     self.patch.assignments.insert(location, value);
                 }
@@ -781,7 +996,7 @@ impl<'mir, 'tcx>
 
     fn visit_terminator_before_primary_effect(
         &mut self,
-        results: &mut Results<'tcx, ValueAnalysisWrapper<ConstAnalysis<'_, 'tcx>>>,
+        results: &mut Results<'tcx, ConstAnalysis<'_, 'tcx>>,
         state: &Self::Domain,
         terminator: &'mir Terminator<'tcx>,
         location: Location,
@@ -789,8 +1004,8 @@ impl<'mir, 'tcx>
         OperandCollector {
             state,
             visitor: self,
-            ecx: &mut results.analysis.0.ecx,
-            map: &results.analysis.0.map,
+            ecx: &mut results.analysis.ecx,
+            map: &results.analysis.map,
         }
         .visit_terminator(terminator, location);
     }