[PERF] further drop changes

src/librustc_mir/dataflow/move_paths/builder.rs

@@ -361,17 +361,14 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
     fn gather_terminator(&mut self, term: &Terminator<'tcx>) {
         match term.kind {
             TerminatorKind::Goto { target: _ }
+            | TerminatorKind::Return
             | TerminatorKind::Resume
             | TerminatorKind::Abort
             | TerminatorKind::GeneratorDrop
             | TerminatorKind::FalseEdges { .. }
             | TerminatorKind::FalseUnwind { .. }
             | TerminatorKind::Unreachable => {}
 
-            TerminatorKind::Return => {
-                self.gather_move(&Place::return_place());
-            }
-
             TerminatorKind::Assert { ref cond, .. } => {
                 self.gather_operand(cond);
             }

src/librustc_mir/util/elaborate_drops.rs

@@ -163,8 +163,6 @@ where
                     .patch_terminator(bb, TerminatorKind::Goto { target: self.succ });
             }
             DropStyle::Static => {
-                let loc = self.terminator_loc(bb);
-                self.elaborator.clear_drop_flag(loc, self.path, DropFlagMode::Deep);
                 self.elaborator.patch().patch_terminator(
                     bb,
                     TerminatorKind::Drop {
@@ -175,9 +173,7 @@ where
                 );
             }
             DropStyle::Conditional => {
-                let unwind = self.unwind; // FIXME(#43234)
-                let succ = self.succ;
-                let drop_bb = self.complete_drop(Some(DropFlagMode::Deep), succ, unwind);
+                let drop_bb = self.complete_drop(self.succ, self.unwind);
                 self.elaborator
                     .patch()
                     .patch_terminator(bb, TerminatorKind::Goto { target: drop_bb });
@@ -249,7 +245,7 @@ where
                 // our own drop flag.
                 path: self.path,
             }
-            .complete_drop(None, succ, unwind)
+            .complete_drop(succ, unwind)
         }
     }
 
@@ -280,13 +276,7 @@ where
         // Clear the "master" drop flag at the end. This is needed
         // because the "master" drop protects the ADT's discriminant,
         // which is invalidated after the ADT is dropped.
-        let (succ, unwind) = (self.succ, self.unwind); // FIXME(#43234)
-        (
-            self.drop_flag_reset_block(DropFlagMode::Shallow, succ, unwind),
-            unwind.map(|unwind| {
-                self.drop_flag_reset_block(DropFlagMode::Shallow, unwind, Unwind::InCleanup)
-            }),
-        )
+        (self.drop_flag_reset_block(DropFlagMode::Shallow, self.succ, self.unwind), self.unwind)
     }
 
     /// Creates a full drop ladder, consisting of 2 connected half-drop-ladders
@@ -813,11 +803,7 @@ where
                     self.open_drop_for_adt(def, substs)
                 }
             }
-            ty::Dynamic(..) => {
-                let unwind = self.unwind; // FIXME(#43234)
-                let succ = self.succ;
-                self.complete_drop(Some(DropFlagMode::Deep), succ, unwind)
-            }
+            ty::Dynamic(..) => self.complete_drop(self.succ, self.unwind),
             ty::Array(ety, size) => {
                 let size = size.try_eval_usize(self.tcx(), self.elaborator.param_env());
                 self.open_drop_for_array(ety, size)
@@ -829,26 +815,14 @@ where
     }
 
     /// Returns a basic block that drop a place using the context
-    /// and path in `c`. If `mode` is something, also clear `c`
-    /// according to it.
+    /// and path in `c`.
     ///
     /// if FLAG(self.path)
-    ///     if let Some(mode) = mode: FLAG(self.path)[mode] = false
     ///     drop(self.place)
-    fn complete_drop(
-        &mut self,
-        drop_mode: Option<DropFlagMode>,
-        succ: BasicBlock,
-        unwind: Unwind,
-    ) -> BasicBlock {
-        debug!("complete_drop({:?},{:?})", self, drop_mode);
+    fn complete_drop(&mut self, succ: BasicBlock, unwind: Unwind) -> BasicBlock {
+        debug!("complete_drop(succ={:?}, unwind={:?})", succ, unwind);
 
         let drop_block = self.drop_block(succ, unwind);
-        let drop_block = if let Some(mode) = drop_mode {
-            self.drop_flag_reset_block(mode, drop_block, unwind)
-        } else {
-            drop_block
-        };
 
         self.drop_flag_test_block(drop_block, succ, unwind)
     }
@@ -861,6 +835,11 @@ where
     ) -> BasicBlock {
         debug!("drop_flag_reset_block({:?},{:?})", self, mode);
 
+        if unwind.is_cleanup() {
+            // The drop flag isn't read again on the unwind path, so don't
+            // bother setting it.
+            return succ;
+        }
         let block = self.new_block(unwind, TerminatorKind::Goto { target: succ });
         let block_start = Location { block: block, statement_index: 0 };
         self.elaborator.clear_drop_flag(block_start, self.path, mode);
@@ -964,11 +943,6 @@ where
         self.elaborator.patch().new_temp(ty, self.source_info.span)
     }
 
-    fn terminator_loc(&mut self, bb: BasicBlock) -> Location {
-        let body = self.elaborator.body();
-        self.elaborator.patch().terminator_loc(body, bb)
-    }
-
     fn constant_usize(&self, val: u16) -> Operand<'tcx> {
         Operand::Constant(box Constant {
             span: self.source_info.span,

src/librustc_mir/util/graphviz.rs

@@ -97,12 +97,17 @@ where
     write!(w, r#"<table border="0" cellborder="1" cellspacing="0">"#)?;
 
     // Basic block number at the top.
+    let (blk, color) = if data.is_cleanup {
+        (format!("{} (cleanup)", block.index()), "lightblue")
+    } else {
+        (format!("{}", block.index()), "gray")
+    };
     write!(
         w,
-        r#"<tr><td {attrs} colspan="{colspan}">{blk}</td></tr>"#,
-        attrs = r#"bgcolor="gray" align="center""#,
+        r#"<tr><td bgcolor="{color}" align="center" colspan="{colspan}">{blk}</td></tr>"#,
         colspan = num_cols,
-        blk = block.index()
+        blk = blk,
+        color = color
     )?;
 
     init(w)?;

src/librustc_mir_build/build/block.rs

@@ -2,6 +2,7 @@ use crate::build::matches::ArmHasGuard;
 use crate::build::ForGuard::OutsideGuard;
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 use crate::hair::*;
+use rustc::middle::region;
 use rustc::mir::*;
 use rustc_hir as hir;
 use rustc_span::Span;
@@ -10,6 +11,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     crate fn ast_block(
         &mut self,
         destination: &Place<'tcx>,
+        scope: Option<region::Scope>,
         block: BasicBlock,
         ast_block: &'tcx hir::Block<'tcx>,
         source_info: SourceInfo,
@@ -26,16 +28,19 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         self.in_opt_scope(opt_destruction_scope.map(|de| (de, source_info)), move |this| {
             this.in_scope((region_scope, source_info), LintLevel::Inherited, move |this| {
                 if targeted_by_break {
-                    // This is a `break`-able block
-                    let exit_block = this.cfg.start_new_block();
-                    let block_exit =
-                        this.in_breakable_scope(None, exit_block, destination.clone(), |this| {
-                            this.ast_block_stmts(destination, block, span, stmts, expr, safety_mode)
-                        });
-                    this.cfg.goto(unpack!(block_exit), source_info, exit_block);
-                    exit_block.unit()
+                    this.in_breakable_scope(None, destination.clone(), scope, span, |this| {
+                        Some(this.ast_block_stmts(
+                            destination,
+                            scope,
+                            block,
+                            span,
+                            stmts,
+                            expr,
+                            safety_mode,
+                        ))
+                    })
                 } else {
-                    this.ast_block_stmts(destination, block, span, stmts, expr, safety_mode)
+                    this.ast_block_stmts(destination, scope, block, span, stmts, expr, safety_mode)
                 }
             })
         })
@@ -44,6 +49,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     fn ast_block_stmts(
         &mut self,
         destination: &Place<'tcx>,
+        scope: Option<region::Scope>,
         mut block: BasicBlock,
         span: Span,
         stmts: Vec<StmtRef<'tcx>>,
@@ -175,7 +181,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 destination_ty.is_unit() || this.block_context.currently_ignores_tail_results();
             this.block_context.push(BlockFrame::TailExpr { tail_result_is_ignored });
 
-            unpack!(block = this.into(destination, block, expr));
+            unpack!(block = this.into(destination, scope, block, expr));
             let popped = this.block_context.pop();
 
             assert!(popped.map_or(false, |bf| bf.is_tail_expr()));

src/librustc_mir_build/build/expr/as_rvalue.rs

@@ -111,12 +111,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
                 this.cfg.push_assign(block, source_info, &Place::from(result), box_);
 
-                // initialize the box contents:
+                // Initialize the box contents. No scope is needed since the
+                // `Box` is already scheduled to be dropped.
                 unpack!(
                     block = this.into(
                         &this.hir.tcx().mk_place_deref(Place::from(result)),
+                        None,
                         block,
-                        value
+                        value,
                     )
                 );
                 block.and(Rvalue::Use(Operand::Move(Place::from(result))))

src/librustc_mir_build/build/expr/as_temp.rs

@@ -100,11 +100,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
         }
 
-        unpack!(block = this.into(temp_place, block, expr));
-
-        if let Some(temp_lifetime) = temp_lifetime {
-            this.schedule_drop(expr_span, temp_lifetime, temp, DropKind::Value);
-        }
+        unpack!(block = this.into(temp_place, temp_lifetime, block, expr));
 
         block.and(temp)
     }