[drop tracking] Visit break expressions

This fixes #102383 by remembering to visit the expression in
`break expr` when building the drop tracking CFG. Missing this step was
causing an off-by-one error which meant after a number of awaits we'd be
looking for dropped values at the wrong point in the code.

Additionally, this changes the order of traversal for assignment
expressions to visit the rhs and then the lhs. This matches what is done
elsewhere.

diff --git a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_build.rs b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_build.rs
index 16806fdba4fbc2113c766be2ed489c032b5f1fda..b3dd3031db2a98d75780d00288364133be6041f4 100644 (file)
--- a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_build.rs
+++ b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_build.rs
@@ -304,8 +304,8 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
         let mut reinit = None;
         match expr.kind {
             ExprKind::Assign(lhs, rhs, _) => {
-                self.visit_expr(lhs);
                 self.visit_expr(rhs);
+                self.visit_expr(lhs);
 
                 reinit = Some(lhs);
             }
@@ -433,7 +433,7 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
                     self.drop_ranges.add_control_edge(self.expr_index, *target)
                 }),
 
-            ExprKind::Break(destination, ..) => {
+            ExprKind::Break(destination, value) => {
                 // destination either points to an expression or to a block. We use
                 // find_target_expression_from_destination to use the last expression of the block
                 // if destination points to a block.
@@ -443,7 +443,11 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
                 // will refer to the end of the block due to the post order traversal.
                 self.find_target_expression_from_destination(destination).map_or((), |target| {
                     self.drop_ranges.add_control_edge_hir_id(self.expr_index, target)
-                })
+                });
+
+                if let Some(value) = value {
+                    self.visit_expr(value);
+                }
             }
 
             ExprKind::Call(f, args) => {
@@ -465,6 +469,12 @@ fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
 
             ExprKind::AddrOf(..)
             | ExprKind::Array(..)
+            // FIXME(eholk): We probably need special handling for AssignOps. The ScopeTree builder
+            // in region.rs runs both lhs then rhs and rhs then lhs and then sets all yields to be
+            // the latest they show up in either traversal. With the older scope-based
+            // approximation, this was fine, but it's probably not right now. What we probably want
+            // to do instead is still run both orders, but consider anything that showed up as a
+            // yield in either order.
             | ExprKind::AssignOp(..)
             | ExprKind::Binary(..)
             | ExprKind::Block(..)
@@ -502,6 +512,9 @@ fn visit_pat(&mut self, pat: &'tcx hir::Pat<'tcx>) {
 
         // Increment expr_count here to match what InteriorVisitor expects.
         self.expr_index = self.expr_index + 1;
+
+        // Save a node mapping to get better CFG visualization
+        self.drop_ranges.add_node_mapping(pat.hir_id, self.expr_index);
     }
 }
 
@@ -521,7 +534,7 @@ fn new(
                 }
             });
         }
-        debug!("hir_id_map: {:?}", tracked_value_map);
+        debug!("hir_id_map: {:#?}", tracked_value_map);
         let num_values = tracked_value_map.len();
         Self {
             tracked_value_map,

diff --git a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_visualize.rs b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_visualize.rs
index c0a0bfe8e1c00a98cb53dd41b5d1e6e9bb7ba82c..e8d31be79d9c9fccff6d6722db6cadf044cbb7a8 100644 (file)
--- a/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_visualize.rs
+++ b/compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_visualize.rs
@@ -2,6 +2,7 @@
 //! flow graph when needed for debugging.
 
 use rustc_graphviz as dot;
+use rustc_hir::{Expr, ExprKind, Node};
 use rustc_middle::ty::TyCtxt;
 
 use super::{DropRangesBuilder, PostOrderId};
@@ -80,10 +81,14 @@ fn node_label(&'a self, n: &Self::Node) -> dot::LabelText<'a> {
                     .post_order_map
                     .iter()
                     .find(|(_hir_id, &post_order_id)| post_order_id == *n)
-                    .map_or("<unknown>".into(), |(hir_id, _)| self
-                        .tcx
-                        .hir()
-                        .node_to_string(*hir_id))
+                    .map_or("<unknown>".into(), |(hir_id, _)| format!(
+                        "{}{}",
+                        self.tcx.hir().node_to_string(*hir_id),
+                        match self.tcx.hir().find(*hir_id) {
+                            Some(Node::Expr(Expr { kind: ExprKind::Yield(..), .. })) => " (yield)",
+                            _ => "",
+                        }
+                    ))
             )
             .into(),
         )

diff --git a/compiler/rustc_hir_typeck/src/generator_interior/mod.rs b/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
index 7990d95310be59489989d8d4753c74b39aaa7eb1..7af5260538568c0d873ad2767cdbb903e5a6517e 100644 (file)
--- a/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
+++ b/compiler/rustc_hir_typeck/src/generator_interior/mod.rs
@@ -71,10 +71,8 @@ fn record(
                                 yield_data.expr_and_pat_count, self.expr_count, source_span
                             );
 
-                            if self.fcx.sess().opts.unstable_opts.drop_tracking
-                                && self
-                                    .drop_ranges
-                                    .is_dropped_at(hir_id, yield_data.expr_and_pat_count)
+                            if self
+                                .is_dropped_at_yield_location(hir_id, yield_data.expr_and_pat_count)
                             {
                                 debug!("value is dropped at yield point; not recording");
                                 return false;
@@ -173,6 +171,18 @@ fn record(
             }
         }
     }
+
+    /// If drop tracking is enabled, consult drop_ranges to see if a value is
+    /// known to be dropped at a yield point and therefore can be omitted from
+    /// the generator witness.
+    fn is_dropped_at_yield_location(&self, value_hir_id: HirId, yield_location: usize) -> bool {
+        // short-circuit if drop tracking is not enabled.
+        if !self.fcx.sess().opts.unstable_opts.drop_tracking {
+            return false;
+        }
+
+        self.drop_ranges.is_dropped_at(value_hir_id, yield_location)
+    }
 }
 
 pub fn resolve_interior<'a, 'tcx>(