Auto merge of #99667 - ouz-a:some_branch, r=oli-obk

Optimize `UnDerefer`

Addresses the performance [issues](https://github.com/rust-lang/rust/pull/98145#issuecomment-1183548597) faced here.

r? `@oli-obk`

compiler/rustc_borrowck/src/lib.rs

@@ -215,7 +215,7 @@ fn do_mir_borrowck<'a, 'tcx>(
 
     let (move_data, move_errors): (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>) =
         match MoveData::gather_moves(&body, tcx, param_env) {
-            Ok(move_data) => (move_data, Vec::new()),
+            Ok((_, move_data)) => (move_data, Vec::new()),
             Err((move_data, move_errors)) => (move_data, move_errors),
         };
     let promoted_errors = promoted

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -1,3 +1,4 @@
+use crate::move_paths::FxHashMap;
 use crate::un_derefer::UnDerefer;
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::tcx::RvalueInitializationState;
@@ -206,10 +207,13 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
     }
 }
 
+pub type MoveDat<'tcx> = Result<
+    (FxHashMap<Local, Place<'tcx>>, MoveData<'tcx>),
+    (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>),
+>;
+
 impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
-    fn finalize(
-        self,
-    ) -> Result<MoveData<'tcx>, (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>)> {
+    fn finalize(self) -> MoveDat<'tcx> {
         debug!("{}", {
             debug!("moves for {:?}:", self.body.span);
             for (j, mo) in self.data.moves.iter_enumerated() {
@@ -222,7 +226,11 @@ impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
             "done dumping moves"
         });
 
-        if !self.errors.is_empty() { Err((self.data, self.errors)) } else { Ok(self.data) }
+        if self.errors.is_empty() {
+            Ok((self.un_derefer.derefer_sidetable, self.data))
+        } else {
+            Err((self.data, self.errors))
+        }
     }
 }
 
@@ -230,7 +238,7 @@ pub(super) fn gather_moves<'tcx>(
     body: &Body<'tcx>,
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-) -> Result<MoveData<'tcx>, (MoveData<'tcx>, Vec<(Place<'tcx>, MoveError<'tcx>)>)> {
+) -> MoveDat<'tcx> {
     let mut builder = MoveDataBuilder::new(body, tcx, param_env);
 
     builder.gather_args();

compiler/rustc_mir_dataflow/src/move_paths/mod.rs

@@ -1,3 +1,4 @@
+use crate::move_paths::builder::MoveDat;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_index::vec::IndexVec;
 use rustc_middle::mir::*;
@@ -386,7 +387,7 @@ impl<'tcx> MoveData<'tcx> {
         body: &Body<'tcx>,
         tcx: TyCtxt<'tcx>,
         param_env: ParamEnv<'tcx>,
-    ) -> Result<Self, (Self, Vec<(Place<'tcx>, MoveError<'tcx>)>)> {
+    ) -> MoveDat<'tcx> {
         builder::gather_moves(body, tcx, param_env)
     }
 

compiler/rustc_mir_dataflow/src/rustc_peek.rs

@@ -30,7 +30,7 @@ impl<'tcx> MirPass<'tcx> for SanityCheck {
         }
 
         let param_env = tcx.param_env(def_id);
-        let move_data = MoveData::gather_moves(body, tcx, param_env).unwrap();
+        let (_, move_data) = MoveData::gather_moves(body, tcx, param_env).unwrap();
         let mdpe = MoveDataParamEnv { move_data, param_env };
 
         if has_rustc_mir_with(tcx, def_id, sym::rustc_peek_maybe_init).is_some() {

compiler/rustc_mir_dataflow/src/un_derefer.rs

@@ -9,6 +9,7 @@ pub struct UnDerefer<'tcx> {
 }
 
 impl<'tcx> UnDerefer<'tcx> {
+    #[inline]
     pub fn derefer(&self, place: PlaceRef<'tcx>, body: &Body<'tcx>) -> Option<Place<'tcx>> {
         let reffed = self.derefer_sidetable.get(&place.local)?;
 
@@ -18,19 +19,4 @@ impl<'tcx> UnDerefer<'tcx> {
         }
         Some(new_place)
     }
-
-    pub fn ref_finder(&mut self, body: &Body<'tcx>) {
-        for (_bb, data) in body.basic_blocks().iter_enumerated() {
-            for stmt in data.statements.iter() {
-                match stmt.kind {
-                    StatementKind::Assign(box (place, Rvalue::CopyForDeref(reffed))) => {
-                        if body.local_decls[place.local].is_deref_temp() {
-                            self.derefer_sidetable.insert(place.local, reffed);
-                        }
-                    }
-                    _ => (),
-                }
-            }
-        }
-    }
 }

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -28,20 +28,19 @@ impl<'tcx> MirPass<'tcx> for ElaborateDrops {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         debug!("elaborate_drops({:?} @ {:?})", body.source, body.span);
 
-        let mut un_derefer = UnDerefer { tcx: tcx, derefer_sidetable: Default::default() };
-        un_derefer.ref_finder(body);
         let def_id = body.source.def_id();
         let param_env = tcx.param_env_reveal_all_normalized(def_id);
-        let move_data = match MoveData::gather_moves(body, tcx, param_env) {
+        let (side_table, move_data) = match MoveData::gather_moves(body, tcx, param_env) {
             Ok(move_data) => move_data,
             Err((move_data, _)) => {
                 tcx.sess.delay_span_bug(
                     body.span,
                     "No `move_errors` should be allowed in MIR borrowck",
                 );
-                move_data
+                (Default::default(), move_data)
             }
         };
+        let un_derefer = UnDerefer { tcx: tcx, derefer_sidetable: side_table };
         let elaborate_patch = {
             let body = &*body;
             let env = MoveDataParamEnv { move_data, param_env };

compiler/rustc_mir_transform/src/remove_uninit_drops.rs

@@ -21,7 +21,7 @@ pub struct RemoveUninitDrops;
 impl<'tcx> MirPass<'tcx> for RemoveUninitDrops {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         let param_env = tcx.param_env(body.source.def_id());
-        let Ok(move_data) = MoveData::gather_moves(body, tcx, param_env) else {
+        let Ok((_,move_data)) = MoveData::gather_moves(body, tcx, param_env) else {
             // We could continue if there are move errors, but there's not much point since our
             // init data isn't complete.
             return;