simplify polonius=next

Remove incomplete handling of kills during traversal for loan liveness
to get to a simpler and actionable prototype.

This handles the cases, on sufficiently simple examples, that were
deferred from NLLs (NLL problem case 3, lending iterators), and is still
a good step to put in people's hands without needing to wait for another
full implementation. This is a practical cut in scope, but it also
shows where are the areas of improvement, that we will explore in the
future.

1 files changed, 2 insertions, 4 deletions

diff --git a/compiler/rustc_borrowck/src/polonius/mod.rs b/compiler/rustc_borrowck/src/polonius/mod.rs
index 142ef8ba28e..a9092b1981e 100644
--- a/compiler/rustc_borrowck/src/polonius/mod.rs
+++ b/compiler/rustc_borrowck/src/polonius/mod.rs
@@ -146,8 +146,8 @@ impl PoloniusContext {
     /// - converting NLL typeck constraints to be localized
     /// - encoding liveness constraints
     ///
-    /// Then, this graph is traversed, and combined with kills, reachability is recorded as loan
-    /// liveness, to be used by the loan scope and active loans computations.
+    /// Then, this graph is traversed, reachability is recorded as loan liveness, to be used by the
+    /// loan scope and active loans computations.
     ///
     /// The constraint data will be used to compute errors and diagnostics.
     pub(crate) fn compute_loan_liveness<'tcx>(
@@ -182,8 +182,6 @@ impl PoloniusContext {
         // Now that we have a complete graph, we can compute reachability to trace the liveness of
         // loans for the next step in the chain, the NLL loan scope and active loans computations.
         let live_loans = compute_loan_liveness(
-            tcx,
-            body,
             regioncx.liveness_constraints(),
             regioncx.outlives_constraints(),
             borrow_set,