Add MIR move elimination pass

Author: Amanieu

compiler/rustc_index/src/interval.rs

@@ -374,6 +374,12 @@ impl<R: Idx, C: Step + Idx> SparseIntervalMatrix<R, C> {
         self.rows.iter_enumerated()
     }
 
+    pub fn clear_row(&mut self, row: R) {
+        if let Some(row) = self.rows.get_mut(row) {
+            row.clear();
+        }
+    }
+
     fn ensure_row(&mut self, row: R) -> &mut IntervalSet<C> {
         self.rows.ensure_contains_elem(row, || IntervalSet::new(self.column_size))
     }
@@ -397,6 +403,16 @@ impl<R: Idx, C: Step + Idx> SparseIntervalMatrix<R, C> {
         write_row.union(read_row)
     }
 
+    pub fn disjoint_rows(&self, a: R, b: R) -> bool
+    where
+        C: Step,
+    {
+        let (Some(a), Some(b)) = (self.rows.get(a), self.rows.get(b)) else {
+            return true;
+        };
+        a.disjoint(b)
+    }
+
     pub fn insert_all_into_row(&mut self, row: R) {
         self.ensure_row(row).insert_all();
     }

compiler/rustc_mir_transform/src/dest_prop.rs

@@ -155,7 +155,9 @@ pub(super) struct DestinationPropagation;
 
 impl<'tcx> crate::MirPass<'tcx> for DestinationPropagation {
     fn policy(&self, ctx: &crate::PassCtx<'_>) -> PassPolicy {
-        PassPolicy::optional(ctx.mir_opt_level() >= 2)
+        PassPolicy::optional(
+            ctx.mir_opt_level() >= 2 && !ctx.opts.unstable_opts.mir_move_elimination,
+        )
     }
 
     #[tracing::instrument(level = "trace", skip(self, tcx, body))]

compiler/rustc_mir_transform/src/lib.rs

@@ -164,6 +164,7 @@ declare_passes! {
     mod lower_slice_len : LowerSliceLenCalls;
     mod match_branches : MatchBranchSimplification;
     mod mentioned_items : MentionedItems;
+    mod move_elimination : MoveElimination;
     mod multiple_return_terminators : MultipleReturnTerminators;
     mod post_drop_elaboration : CheckLiveDrops;
     mod prettify : ReorderBasicBlocks, ReorderLocals;
@@ -763,6 +764,7 @@ pub(crate) fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
             &dead_store_elimination::DeadStoreElimination::Final,
             &dest_prop::DestinationPropagation,
             &tail_copy_to_move::TailCopyToMove,
+            &move_elimination::MoveElimination,
             &simplify::SimplifyLocals::Final,
             &multiple_return_terminators::MultipleReturnTerminators,
             // Some cleanup necessary at least for LLVM and potentially other codegen backends.