Introduce drop range tracking to generator interior analysis

Cargo.lock

@@ -4388,13 +4388,15 @@ dependencies = [
  "rustc_attr",
  "rustc_data_structures",
  "rustc_errors",
+ "rustc_graphviz",
  "rustc_hir",
  "rustc_hir_pretty",
  "rustc_index",
  "rustc_infer",
  "rustc_lint",
  "rustc_macros",
  "rustc_middle",
+ "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_middle/src/middle/region.rs

@@ -308,7 +308,7 @@ pub struct ScopeTree {
     /// The reason is that semantically, until the `box` expression returns,
     /// the values are still owned by their containing expressions. So
     /// we'll see that `&x`.
-    pub yield_in_scope: FxHashMap<Scope, YieldData>,
+    pub yield_in_scope: FxHashMap<Scope, Vec<YieldData>>,
 
     /// The number of visit_expr and visit_pat calls done in the body.
     /// Used to sanity check visit_expr/visit_pat call count when
@@ -423,8 +423,8 @@ impl ScopeTree {
 
     /// Checks whether the given scope contains a `yield`. If so,
     /// returns `Some(YieldData)`. If not, returns `None`.
-    pub fn yield_in_scope(&self, scope: Scope) -> Option<YieldData> {
-        self.yield_in_scope.get(&scope).cloned()
+    pub fn yield_in_scope(&self, scope: Scope) -> Option<&Vec<YieldData>> {
+        self.yield_in_scope.get(&scope)
     }
 
     /// Gives the number of expressions visited in a body.

compiler/rustc_passes/src/region.rs

@@ -366,7 +366,8 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
             let target_scopes = visitor.fixup_scopes.drain(start_point..);
 
             for scope in target_scopes {
-                let mut yield_data = visitor.scope_tree.yield_in_scope.get_mut(&scope).unwrap();
+                let mut yield_data =
+                    visitor.scope_tree.yield_in_scope.get_mut(&scope).unwrap().last_mut().unwrap();
                 let count = yield_data.expr_and_pat_count;
                 let span = yield_data.span;
 
@@ -429,7 +430,13 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
             };
             let data =
                 YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source };
-            visitor.scope_tree.yield_in_scope.insert(scope, data);
+            match visitor.scope_tree.yield_in_scope.get_mut(&scope) {
+                Some(yields) => yields.push(data),
+                None => {
+                    visitor.scope_tree.yield_in_scope.insert(scope, vec![data]);
+                }
+            }
+
             if visitor.pessimistic_yield {
                 debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope);
                 visitor.fixup_scopes.push(scope);

compiler/rustc_typeck/Cargo.toml

@@ -15,6 +15,7 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_attr = { path = "../rustc_attr" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
+rustc_graphviz = { path = "../rustc_graphviz" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_target = { path = "../rustc_target" }
@@ -27,3 +28,4 @@ rustc_infer = { path = "../rustc_infer" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_ty_utils = { path = "../rustc_ty_utils" }
 rustc_lint = { path = "../rustc_lint" }
+rustc_serialize = { path = "../rustc_serialize" }

compiler/rustc_typeck/src/check/generator_interior.rs

@@ -3,6 +3,7 @@
 //! is calculated in `rustc_const_eval::transform::generator` and may be a subset of the
 //! types computed here.
 
+use self::drop_ranges::DropRanges;
 use super::FnCtxt;
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::pluralize;
@@ -19,6 +20,8 @@ use rustc_span::Span;
 use smallvec::SmallVec;
 use tracing::debug;
 
+mod drop_ranges;
+
 struct InteriorVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     types: FxIndexSet<ty::GeneratorInteriorTypeCause<'tcx>>,
@@ -34,6 +37,7 @@ struct InteriorVisitor<'a, 'tcx> {
     guard_bindings: SmallVec<[SmallVec<[HirId; 4]>; 1]>,
     guard_bindings_set: HirIdSet,
     linted_values: HirIdSet,
+    drop_ranges: DropRanges,
 }
 
 impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
@@ -48,9 +52,11 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
     ) {
         use rustc_span::DUMMY_SP;
 
+        let ty = self.fcx.resolve_vars_if_possible(ty);
+
         debug!(
-            "generator_interior: attempting to record type {:?} {:?} {:?} {:?}",
-            ty, scope, expr, source_span
+            "attempting to record type ty={:?}; hir_id={:?}; scope={:?}; expr={:?}; source_span={:?}; expr_count={:?}",
+            ty, hir_id, scope, expr, source_span, self.expr_count,
         );
 
         let live_across_yield = scope
@@ -63,29 +69,34 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
                     //
                     // See the mega-comment at `yield_in_scope` for a proof.
 
-                    debug!(
-                        "comparing counts yield: {} self: {}, source_span = {:?}",
-                        yield_data.expr_and_pat_count, self.expr_count, source_span
-                    );
+                    yield_data
+                        .iter()
+                        .find(|yield_data| {
+                            debug!(
+                                "comparing counts yield: {} self: {}, source_span = {:?}",
+                                yield_data.expr_and_pat_count, self.expr_count, source_span
+                            );
+
+                            if self.drop_ranges.is_dropped_at(hir_id, yield_data.expr_and_pat_count)
+                            {
+                                debug!("value is dropped at yield point; not recording");
+                                return false;
+                            }
 
-                    // If it is a borrowing happening in the guard,
-                    // it needs to be recorded regardless because they
-                    // do live across this yield point.
-                    if guard_borrowing_from_pattern
-                        || yield_data.expr_and_pat_count >= self.expr_count
-                    {
-                        Some(yield_data)
-                    } else {
-                        None
-                    }
+                            // If it is a borrowing happening in the guard,
+                            // it needs to be recorded regardless because they
+                            // do live across this yield point.
+                            guard_borrowing_from_pattern
+                                || yield_data.expr_and_pat_count >= self.expr_count
+                        })
+                        .cloned()
                 })
             })
             .unwrap_or_else(|| {
                 Some(YieldData { span: DUMMY_SP, expr_and_pat_count: 0, source: self.kind.into() })
             });
 
         if let Some(yield_data) = live_across_yield {
-            let ty = self.fcx.resolve_vars_if_possible(ty);
             debug!(
                 "type in expr = {:?}, scope = {:?}, type = {:?}, count = {}, yield_span = {:?}",
                 expr, scope, ty, self.expr_count, yield_data.span
@@ -154,7 +165,6 @@ impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
                 self.expr_count,
                 expr.map(|e| e.span)
             );
-            let ty = self.fcx.resolve_vars_if_possible(ty);
             if let Some((unresolved_type, unresolved_type_span)) =
                 self.fcx.unresolved_type_vars(&ty)
             {
@@ -186,6 +196,7 @@ pub fn resolve_interior<'a, 'tcx>(
         guard_bindings: <_>::default(),
         guard_bindings_set: <_>::default(),
         linted_values: <_>::default(),
+        drop_ranges: drop_ranges::compute_drop_ranges(fcx, def_id, body),
     };
     intravisit::walk_body(&mut visitor, body);
 
@@ -313,6 +324,7 @@ impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
 
     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
         let mut guard_borrowing_from_pattern = false;
+
         match &expr.kind {
             ExprKind::Call(callee, args) => match &callee.kind {
                 ExprKind::Path(qpath) => {