Only allow propagating integers.

Author: cjgillot

compiler/rustc_mir_transform/src/const_prop.rs

@@ -135,7 +135,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp {
                         FlatSet::Top
                     };
 
-                    if let FlatSet::Elem(value) = value {
+                    if let FlatSet::Elem(value) = value && value.can_const_prop() {
                         collector.assignments.insert(location, value);
                     }
                 }

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -354,6 +354,12 @@ impl<'tcx> std::fmt::Debug for ScalarTy<'tcx> {
     }
 }
 
+impl<'tcx> ScalarTy<'tcx> {
+    pub fn can_const_prop(&self) -> bool {
+        self.0.try_to_int().is_ok()
+    }
+}
+
 impl<'a, 'm, 'tcx> ConstAnalysis<'a, 'm, 'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, map: &'m Map) -> Self {
         let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
@@ -527,14 +533,10 @@ impl<'mir, 'tcx>
                 // Don't overwrite the assignment if it already uses a constant (to keep the span).
             }
             StatementKind::Assign(box (place, _)) => {
-                match state.get(place.as_ref(), &results.analysis.0.map) {
-                    FlatSet::Top => (),
-                    FlatSet::Elem(value) => {
-                        self.assignments.insert(location, value);
-                    }
-                    FlatSet::Bottom => {
-                        // This assignment is either unreachable, or an uninitialized value is assigned.
-                    }
+                if let FlatSet::Elem(value) = state.get(place.as_ref(), results.analysis.0.map)
+                    && value.can_const_prop()
+                {
+                    self.assignments.insert(location, value);
                 }
             }
             _ => (),
@@ -560,6 +562,7 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx> {
 
     fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
         if let Some(value) = self.assignments.get(&location) {
+            assert!(value.can_const_prop(), "trying to propagate a pointer");
             match &mut statement.kind {
                 StatementKind::Assign(box (_, rvalue)) => {
                     if !matches!(rvalue, Rvalue::Use(Operand::Constant(_))) {
@@ -578,6 +581,7 @@ impl<'tcx> MutVisitor<'tcx> for CollectAndPatch<'tcx> {
         match operand {
             Operand::Copy(place) | Operand::Move(place) => {
                 if let Some(value) = self.before_effect.get(&(location, *place)) {
+                    assert!(value.can_const_prop(), "trying to propagate a pointer");
                     *operand = self.make_operand(value.clone());
                 } else if !place.projection.is_empty() {
                     self.super_operand(operand, location)
@@ -613,7 +617,9 @@ pub(crate) struct OperandCollector<'tcx, 'map, 'a> {
 impl<'tcx, 'map, 'a> Visitor<'tcx> for OperandCollector<'tcx, 'map, 'a> {
     fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) {
         if let Some(place) = operand.place() {
-            if let FlatSet::Elem(value) = self.state.get(place.as_ref(), self.map) {
+            if let FlatSet::Elem(value) = self.state.get(place.as_ref(), self.map)
+                && value.can_const_prop()
+            {
                 self.visitor.before_effect.insert((location, place), value);
             } else if !place.projection.is_empty() {
                 // Try to propagate into `Index` projections.
@@ -625,6 +631,7 @@ impl<'tcx, 'map, 'a> Visitor<'tcx> for OperandCollector<'tcx, 'map, 'a> {
     fn visit_local(&mut self, local: Local, ctxt: PlaceContext, location: Location) {
         if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy | NonMutatingUseContext::Move) = ctxt
             && let FlatSet::Elem(value) = self.state.get(local.into(), self.map)
+            && value.can_const_prop()
         {
             self.visitor.before_effect.insert((location, local.into()), value);
         }