Auto merge of #50798 - bobtwinkles:nll_facts_invalidate, r=nikomatsakis

Generate "invalidates" facts when -Znll-facts is passed

Most of the new code is copied directly from the heart of the MIR borrowchecker. I was expecting more fundamental structural changes, hence the copying. This appears to work as it stands, but I'd like to submit a follow-up PR to reduce code duplication. I figured that could wait though, since this is blocking a large amount of work in the borrow check repository and I'm out of time for tonight =).

r? @nikomatsakis

src/librustc_mir/borrow_check/nll/facts.rs

@@ -38,6 +38,9 @@
 
     // `region_live_at(R, P)` when the region R appears in a live variable at P
     crate region_live_at: Vec<(RegionVid, LocationIndex)>,
+
+    // `invalidates(P, B)` when the borrow B is invalidated at point P
+    crate invalidates: Vec<(LocationIndex, BorrowIndex)>,
 }
 
 impl AllFacts {
@@ -69,6 +72,7 @@ impl AllFacts {
                 killed,
                 outlives,
                 region_live_at,
+                invalidates,
             ])
         }
         Ok(())

src/librustc_mir/borrow_check/nll/mod.rs

@@ -37,6 +37,7 @@
 mod subtype_constraint_generation;
 crate mod type_check;
 mod universal_regions;
+mod invalidation;
 
 use self::facts::AllFacts;
 use self::region_infer::RegionInferenceContext;
@@ -130,6 +131,14 @@ pub(in borrow_check) fn compute_regions<'cx, 'gcx, 'tcx>(
         &mir,
         borrow_set,
     );
+    invalidation::generate_invalidates(
+        infcx,
+        &mut all_facts,
+        location_table,
+        &mir,
+        def_id,
+        borrow_set
+    );
 
     // Dump facts if requested.
     if let Some(all_facts) = all_facts {