opt_placeholder_loans.diff

diff --git a/polonius-engine/src/output/datafrog_opt.rs b/polonius-engine/src/output/datafrog_opt.rs
index 8140535..7cd39e0 100644
--- a/polonius-engine/src/output/datafrog_opt.rs
+++ b/polonius-engine/src/output/datafrog_opt.rs
@@ -26,6 +26,11 @@ pub(super) fn compute<T: FactTypes>(
         let cfg_edge_rel = &ctx.cfg_edge;
         let killed_rel = &ctx.killed;
 
+        let cfg_node = ctx.cfg_node;
+        let known_contains = &ctx.known_contains;
+        let placeholder_origin = &ctx.placeholder_origin;
+        let placeholder_loan = &ctx.placeholder_loan;
+
         // Create a new iteration context, ...
         let mut iteration = Iteration::new();
 
@@ -125,6 +130,7 @@ pub(super) fn compute<T: FactTypes>(
 
         // .decl errors(loan, point)
         let errors = iteration.variable("errors");
+        let subset_errors = iteration.variable::<(T::Origin, T::Origin, T::Point)>("subset_errors");
 
         // Make "variable" versions of the relations, needed for joins.
         borrow_region_op.extend(
@@ -157,6 +163,20 @@ pub(super) fn compute<T: FactTypes>(
                 .map(|&(origin, loan, point)| ((origin, point), loan)),
         );
 
+        // Placeholder loans are contained by their placeholder origin at all points of the CFG.
+        //
+        // contains(Origin, Loan, Node) :-
+        //   cfg_node(Node),
+        //   placeholder(Origin, Loan).
+        let mut placeholder_loans = Vec::with_capacity(placeholder_loan.len() * cfg_node.len());
+        for &(loan, origin) in placeholder_loan.iter() {
+            for &node in cfg_node.iter() {
+                placeholder_loans.push(((origin, node), loan));
+            }
+        }
+
+        requires_op.extend(placeholder_loans);
+
         // .. and then start iterating rules!
         while iteration.changed() {
             // Cleanup step: remove symmetries
@@ -372,6 +392,25 @@ pub(super) fn compute<T: FactTypes>(
             errors.from_join(&invalidates, &borrow_live_at, |&(loan, point), _, _| {
                 (loan, point)
             });
+
+            // subset_errors(Origin1, Origin2, Point) :-
+            //   requires(Origin2, Loan1, Point),
+            //   placeholder(Origin2, _),
+            //   placeholder(Origin1, Loan1),
+            //   !known_contains(Origin2, Loan1).
+            subset_errors.from_leapjoin(
+                &requires_op,
+                (
+                    placeholder_origin.filter_with(|&((origin2, _point), _loan1)| (origin2, ())),
+                    placeholder_loan.extend_with(|&((_origin2, _point), loan1)| loan1),
+                    known_contains.filter_anti(|&((origin2, _point), loan1)| (origin2, loan1)),
+                    // remove symmetries:
+                    datafrog::ValueFilter::from(|&((origin2, _point), _loan1), &origin1| {
+                        origin2 != origin1
+                    }),
+                ),
+                |&((origin2, point), _loan1), &origin1| (origin1, origin2, point),
+            );
         }
 
         if result.dump_enabled {