optimization round 2

- moved work from `find_local` to `gather_statement`
- created custom iterator for `iter_projections`
- reverted change from `IndexVec` to `FxIndexMap`

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -39,18 +39,18 @@ impl<'a, 'tcx> MoveDataBuilder<'a, 'tcx> {
                     locals: body
                         .local_decls
                         .iter_enumerated()
-                        .filter(|(_, l)| !l.is_deref_temp())
-                        .map(|(i, _)| {
-                            (
-                                i,
+                        .map(|(i, l)| {
+                            if l.is_deref_temp() {
+                                MovePathIndex::MAX
+                            } else {
                                 Self::new_move_path(
                                     &mut move_paths,
                                     &mut path_map,
                                     &mut init_path_map,
                                     None,
                                     Place::from(i),
-                                ),
-                            )
+                                )
+                            }
                         })
                         .collect(),
                     projections: Default::default(),
@@ -285,8 +285,14 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
     fn gather_statement(&mut self, stmt: &Statement<'tcx>) {
         match &stmt.kind {
             StatementKind::Assign(box (place, Rvalue::CopyForDeref(reffed))) => {
-                assert!(self.builder.body.local_decls[place.local].is_deref_temp());
-                self.builder.data.rev_lookup.un_derefer.insert(place.as_local().unwrap(), *reffed);
+                let local = place.as_local().unwrap();
+                assert!(self.builder.body.local_decls[local].is_deref_temp());
+
+                let rev_lookup = &mut self.builder.data.rev_lookup;
+
+                rev_lookup.un_derefer.insert(local, reffed.as_ref());
+                let base_local = rev_lookup.un_derefer.deref_chain(local).first().unwrap().local;
+                rev_lookup.locals[local] = rev_lookup.locals[base_local];
             }
             StatementKind::Assign(box (place, rval)) => {
                 self.create_move_path(*place);

compiler/rustc_mir_dataflow/src/move_paths/mod.rs

@@ -1,6 +1,6 @@
 use crate::move_paths::builder::MoveDat;
 use crate::un_derefer::UnDerefer;
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
+use rustc_data_structures::fx::FxHashMap;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
@@ -291,7 +291,7 @@ impl Init {
 /// Tables mapping from a place to its MovePathIndex.
 #[derive(Debug)]
 pub struct MovePathLookup<'tcx> {
-    locals: FxIndexMap<Local, MovePathIndex>,
+    locals: IndexVec<Local, MovePathIndex>,
 
     /// projections are made from a base-place and a projection
     /// elem. The base-place will have a unique MovePathIndex; we use
@@ -331,17 +331,9 @@ impl<'tcx> MovePathLookup<'tcx> {
         LookupResult::Exact(result)
     }
 
+    #[inline]
     pub fn find_local(&self, local: Local) -> MovePathIndex {
-        let deref_chain = self.un_derefer.deref_chain(local);
-
-        let local = match deref_chain.first() {
-            Some(place) => place.local,
-            None => local,
-        };
-
-        *self.locals.get(&local).unwrap_or_else(|| {
-            bug!("base local ({local:?}) of deref_chain should not be a deref temp")
-        })
+        self.locals[local]
     }
 
     /// An enumerated iterator of `local`s and their associated
@@ -349,7 +341,7 @@ impl<'tcx> MovePathLookup<'tcx> {
     pub fn iter_locals_enumerated(
         &self,
     ) -> impl DoubleEndedIterator<Item = (Local, MovePathIndex)> + ExactSizeIterator + '_ {
-        self.locals.iter().map(|(&l, &idx)| (l, idx))
+        self.locals.iter_enumerated().map(|(l, &idx)| (l, idx))
     }
 }