update comment, rename fn record_operand_moved

the previous name made it seem as if the operand was moved while it's
actually just looking at all `Move` operands.

Author: lcnr

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -197,7 +197,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     )
                 );
                 let result_operand = Operand::Move(Place::from(result));
-                this.record_operands_moved(slice::from_ref(&result_operand));
+                this.record_move_operands(slice::from_ref(&result_operand));
                 block.and(Rvalue::Use(result_operand))
             }
             ExprKind::Cast { source } => {
@@ -366,7 +366,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     })
                     .collect();
 
-                this.record_operands_moved(&fields.raw);
+                this.record_move_operands(&fields.raw);
                 block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(el_ty)), fields))
             }
             ExprKind::Tuple { ref fields } => {
@@ -388,7 +388,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     })
                     .collect();
 
-                this.record_operands_moved(&fields.raw);
+                this.record_move_operands(&fields.raw);
                 block.and(Rvalue::Aggregate(Box::new(AggregateKind::Tuple), fields))
             }
             ExprKind::Closure(box ClosureExpr {
@@ -491,7 +491,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         Box::new(AggregateKind::CoroutineClosure(closure_id.to_def_id(), args))
                     }
                 };
-                this.record_operands_moved(&operands.raw);
+                this.record_move_operands(&operands.raw);
                 block.and(Rvalue::Aggregate(result, operands))
             }
             ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => {
@@ -747,7 +747,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 this.diverge_from(block);
                 block = success;
             }
-            this.record_operands_moved(&[value_operand]);
+            this.record_move_operands(&[value_operand]);
         }
         block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(elem_ty)), IndexVec::new()))
     }

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -314,11 +314,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 );
                 this.diverge_from(block);
 
-                // This is here and not before `diverge_from` to avoid breaking
-                // the example in #80949.
+                // By only recording the moved operands after `diverge_from`, we emit redundant
+                // drop calls for the arguments of the call. While these should be unnecessary,
+                // they cause borrowck to shrink the required lifetime of some borrows which is
+                // necessary to avoid breaking the example in #80949.
                 // FIXME(matthewjasper): Look at this again if Polonius is
                 // stabilized.
-                this.record_operands_moved(&args);
+                this.record_move_operands(&args);
                 schedule_drop(this);
                 success.unit()
             }
@@ -419,7 +421,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     user_ty,
                     active_field_index,
                 ));
-                this.record_operands_moved(&fields.raw);
+                this.record_move_operands(&fields.raw);
                 this.cfg.push_assign(
                     block,
                     source_info,
@@ -602,7 +604,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     )
                 );
                 let resume = this.cfg.start_new_block();
-                this.record_operands_moved(slice::from_ref(&value));
+                this.record_move_operands(slice::from_ref(&value));
                 this.cfg.terminate(
                     block,
                     source_info,

compiler/rustc_mir_build/src/build/expr/stmt.rs

@@ -116,7 +116,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         .collect();
                     let args: Vec<_> = spanned_args.iter().map(|arg| arg.node.clone()).collect();
 
-                    this.record_operands_moved(&args);
+                    this.record_move_operands(&args);
 
                     debug!("expr_into_dest: fn_span={:?}", fn_span);
 

compiler/rustc_mir_build/src/build/scope.rs

@@ -1009,13 +1009,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         region_scope: region::Scope,
         local: Local,
     ) {
+        // We first drop the value and then the underlying storage.
         self.schedule_drop(span, region_scope, local, DropKind::Storage);
         self.schedule_drop(span, region_scope, local, DropKind::Value);
     }
 
-    /// Indicates that `place` should be dropped on exit from `region_scope`.
+    /// Indicates that `local` should be dropped on exit from `region_scope`.
     ///
-    /// When called with `DropKind::Storage`, `place` shouldn't be the return
+    /// When called with `DropKind::Storage`, `local` shouldn't be the return
     /// place, or a function parameter.
     pub(crate) fn schedule_drop(
         &mut self,
@@ -1121,7 +1122,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     }
 
     /// Unschedule a drop. Used for `break`, `return` and `match` expressions,
-    /// where `record_operands_moved` is not powerful enough.
+    /// where `record_move_operands` is not powerful enough.
     ///
     /// The given local is expected to have a value drop scheduled in the given
     /// scope and for that drop to be the most recent thing scheduled in that
@@ -1146,8 +1147,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     // type does not need drop.
                     None if self.local_decls[local].ty.has_opaque_types() => return,
                     _ => bug!(
-                        "found wrong drop, expected value drop of {:?}, found {:?}",
+                        "found wrong drop, expected value drop of {:?} in scope {:?}, found {:?}",
                         local,
+                        region_scope,
                         drop,
                     ),
                 }
@@ -1192,7 +1194,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// spurious borrow-check errors -- the problem, ironically, is
     /// not the `DROP(_X)` itself, but the (spurious) unwind pathways
     /// that it creates. See #64391 for an example.
-    pub(crate) fn record_operands_moved(&mut self, operands: &[Operand<'tcx>]) {
+    pub(crate) fn record_move_operands(&mut self, operands: &[Operand<'tcx>]) {
         let local_scope = self.local_scope();
         let scope = self.scopes.scopes.last_mut().unwrap();