Fix handling of (in)variance in GenerateConstraintsForAssignment.
PiperOrigin-RevId: 471754088
diff --git a/lifetime_analysis/lifetime_analysis.cc b/lifetime_analysis/lifetime_analysis.cc
index 5ae2d1e..5b8d702 100644
--- a/lifetime_analysis/lifetime_analysis.cc
+++ b/lifetime_analysis/lifetime_analysis.cc
@@ -103,7 +103,8 @@
void GenerateConstraintsForAssignmentImpl(
const ObjectSet& pointers, const ObjectSet& new_pointees,
clang::QualType pointer_type, const ObjectRepository& object_repository,
- PointsToMap& points_to_map, LifetimeConstraints& constraints,
+ const PointsToMap& points_to_map, bool is_in_invariant_context,
+ LifetimeConstraints& constraints,
llvm::DenseSet<std::pair<const Object*, const Object*>>& seen_pairs) {
// Check for cycles.
{
@@ -137,10 +138,9 @@
}
}
- // If this pointer is not const, the objects appear in invariant position,
- // thus we need to insert constraints in the opposite direction too (i.e. we
- // need equality).
- if (!pointer_type.isConstQualified()) {
+ // If we are in an invariant context, we need to insert constraints in the
+ // opposite direction too (i.e. we need equality).
+ if (is_in_invariant_context) {
for (const Object* old : old_pointees) {
for (const Object* newp : new_pointees) {
constraints.AddOutlivesConstraint(newp->GetLifetime(),
@@ -149,6 +149,11 @@
}
}
+ // See https://doc.rust-lang.org/nomicon/subtyping.html for an explanation of
+ // variance; here in particular, we use the fact that the pointee of a pointer
+ // is covariant if the pointer is const-qualified, and invariant otherwise.
+ is_in_invariant_context = !pointer_type.isConstQualified();
+
// Recurse in pointees. As the pointee might be of struct type, we need first
// to extract all field pointers from it.
struct RecursiveVisitInfo {
@@ -190,7 +195,8 @@
GenerateConstraintsForAssignmentImpl(
call.old_pointees,
points_to_map.GetPointerPointsToSet(call.new_pointees), call.type,
- object_repository, points_to_map, constraints, seen_pairs);
+ object_repository, points_to_map, is_in_invariant_context,
+ constraints, seen_pairs);
}
}
}
@@ -202,9 +208,10 @@
PointsToMap& points_to_map,
LifetimeConstraints& constraints) {
llvm::DenseSet<std::pair<const Object*, const Object*>> seen_pairs;
- GenerateConstraintsForAssignmentImpl(pointers, new_pointees, pointer_type,
- object_repository, points_to_map,
- constraints, seen_pairs);
+ // Outer-most pointers are never invariant.
+ GenerateConstraintsForAssignmentImpl(
+ pointers, new_pointees, pointer_type, object_repository, points_to_map,
+ /*is_in_invariant_context=*/false, constraints, seen_pairs);
}
void HandlePointsToSetExtension(const ObjectSet& pointers,
