and more

warning: this argument is a mutable reference, but not used mutably
    --> compiler\rustc_mir_transform\src\coroutine.rs:1229:11
     |
1229 |     body: &mut Body<'tcx>,
     |           ^^^^^^^^^^^^^^^ help: consider changing to: `&Body<'tcx>`
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut

warning: this argument is a mutable reference, but not used mutably
   --> compiler\rustc_mir_transform\src\nrvo.rs:123:11
    |
123 |     body: &mut mir::Body<'_>,
    |           ^^^^^^^^^^^^^^^^^^ help: consider changing to: `&mir::Body<'_>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut

warning: this argument is a mutable reference, but not used mutably
  --> compiler\rustc_mir_transform\src\nrvo.rs:87:34
   |
87 | fn local_eligible_for_nrvo(body: &mut mir::Body<'_>) -> Option<Local> {
   |                                  ^^^^^^^^^^^^^^^^^^ help: consider changing to: `&mir::Body<'_>`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1595,10 +1595,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// [`Switch`]: TestKind::Switch
     /// [`SwitchInt`]: TestKind::SwitchInt
     /// [`Range`]: TestKind::Range
-    fn pick_test(
+    fn pick_test(&mut self, candidates: &[&mut Candidate<'_, 'tcx>]) -> (Place<'tcx>, Test<'tcx>) {
-        &mut self,
-        candidates: &mut [&mut Candidate<'_, 'tcx>],
-    ) -> (Place<'tcx>, Test<'tcx>) {
         // Extract the match-pair from the highest priority candidate
         let match_pair = &candidates.first().unwrap().match_pairs[0];
         let test = self.test(match_pair);

compiler/rustc_mir_transform/src/coroutine.rs

@@ -1226,7 +1226,7 @@ fn create_coroutine_drop_shim<'tcx>(
     tcx: TyCtxt<'tcx>,
     transform: &TransformVisitor<'tcx>,
     coroutine_ty: Ty<'tcx>,
-    body: &mut Body<'tcx>,
+    body: &Body<'tcx>,
     drop_clean: BasicBlock,
 ) -> Body<'tcx> {
     let mut body = body.clone();

compiler/rustc_mir_transform/src/nrvo.rs

@@ -84,7 +84,7 @@ impl<'tcx> MirPass<'tcx> for RenameReturnPlace {
 ///
 /// If the MIR fulfills both these conditions, this function returns the `Local` that is assigned
 /// to the return place along all possible paths through the control-flow graph.
-fn local_eligible_for_nrvo(body: &mut mir::Body<'_>) -> Option<Local> {
+fn local_eligible_for_nrvo(body: &mir::Body<'_>) -> Option<Local> {
     if IsReturnPlaceRead::run(body) {
         return None;
     }
@@ -118,10 +118,7 @@ fn local_eligible_for_nrvo(body: &mut mir::Body<'_>) -> Option<Local> {
     copied_to_return_place
 }
 
-fn find_local_assigned_to_return_place(
+fn find_local_assigned_to_return_place(start: BasicBlock, body: &mir::Body<'_>) -> Option<Local> {
-    start: BasicBlock,
-    body: &mut mir::Body<'_>,
-) -> Option<Local> {
     let mut block = start;
     let mut seen = BitSet::new_empty(body.basic_blocks.len());