introduce borrowed locals analysis based on liveness analysis

Author: b-naber

Cargo.lock

@@ -3760,6 +3760,7 @@ dependencies = [
 name = "rustc_mir_dataflow"
 version = "0.0.0"
 dependencies = [
+ "either",
  "polonius-engine",
  "regex",
  "rustc_ast",

compiler/rustc_mir_dataflow/Cargo.toml

@@ -22,3 +22,4 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_target = { path = "../rustc_target" }
 rustc_span = { path = "../rustc_span" }
+either = "1"

compiler/rustc_mir_dataflow/src/framework/cursor.rs

@@ -140,7 +140,6 @@ where
     }
 
     /// Allows inspection of unreachable basic blocks even with `debug_assertions` enabled.
-    #[cfg(test)]
     pub(crate) fn allow_unreachable(&mut self) {
         #[cfg(debug_assertions)]
         self.reachable_blocks.insert_all()