Diagnose liveness on MIR.

Author: cjgillot

compiler/rustc_interface/src/passes.rs

@@ -990,6 +990,7 @@ fn run_required_analyses(tcx: TyCtxt<'_>) {
                 tcx.ensure_ok().mir_borrowck(def_id)
             }
             tcx.ensure_ok().has_ffi_unwind_calls(def_id);
+            tcx.ensure_ok().check_liveness(def_id);
 
             // If we need to codegen, ensure that we emit all errors from
             // `mir_drops_elaborated_and_const_checked` now, to avoid discovering

compiler/rustc_middle/src/mir/mod.rs

@@ -937,7 +937,7 @@ pub enum BindingForm<'tcx> {
     /// Binding for a `self`/`&self`/`&mut self` binding where the type is implicit.
     ImplicitSelf(ImplicitSelfKind),
     /// Reference used in a guard expression to ensure immutability.
-    RefForGuard,
+    RefForGuard(Local),
 }
 
 mod binding_form_impl {
@@ -952,7 +952,7 @@ mod binding_form_impl {
             match self {
                 Var(binding) => binding.hash_stable(hcx, hasher),
                 ImplicitSelf(kind) => kind.hash_stable(hcx, hasher),
-                RefForGuard => (),
+                RefForGuard(local) => local.hash_stable(hcx, hasher),
             }
         }
     }
@@ -1163,7 +1163,7 @@ impl<'tcx> LocalDecl<'tcx> {
     /// expression that is used to access said variable for the guard of the
     /// match arm.
     pub fn is_ref_for_guard(&self) -> bool {
-        matches!(self.local_info(), LocalInfo::User(BindingForm::RefForGuard))
+        matches!(self.local_info(), LocalInfo::User(BindingForm::RefForGuard(_)))
     }
 
     /// Returns `Some` if this is a reference to a static item that is used to