Do not ICE on deeply nested borrows.

1 files changed, 4 insertions, 2 deletions

diff --git a/compiler/rustc_mir_transform/src/ref_prop.rs b/compiler/rustc_mir_transform/src/ref_prop.rs
index b0f89393989..bbd9f76ba5c 100644
--- a/compiler/rustc_mir_transform/src/ref_prop.rs
+++ b/compiler/rustc_mir_transform/src/ref_prop.rs
@@ -363,8 +363,10 @@ impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> {
             if let Some((&PlaceElem::Deref, rest)) = target.projection.split_last() {
                 *place = Place::from(target.local).project_deeper(rest, self.tcx);
                 self.any_replacement = true;
-            } else if self.fully_replacable_locals.contains(place.local) {
-                debuginfo.references += 1;
+            } else if self.fully_replacable_locals.contains(place.local)
+                && let Some(references) = debuginfo.references.checked_add(1)
+            {
+                debuginfo.references = references;
                 *place = target;
                 self.any_replacement = true;
             }