Revert "Defer creating drop trees in MIR lowering until leaving that scope"

This reverts commit 6119885.

Author: pnkfelix

src/librustc_mir/util/graphviz.rs

@@ -97,17 +97,12 @@ 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 bgcolor="{color}" align="center" colspan="{colspan}">{blk}</td></tr>"#,
+        r#"<tr><td {attrs} colspan="{colspan}">{blk}</td></tr>"#,
+        attrs = r#"bgcolor="gray" align="center""#,
         colspan = num_cols,
-        blk = blk,
-        color = color
+        blk = block.index()
     )?;
 
     init(w)?;

src/librustc_mir_build/build/block.rs

@@ -28,16 +28,14 @@ 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.in_breakable_scope(None, destination, span, |this| {
-                        Some(this.ast_block_stmts(
-                            destination,
-                            block,
-                            span,
-                            stmts,
-                            expr,
-                            safety_mode,
-                        ))
-                    })
+                    // 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, |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()
                 } else {
                     this.ast_block_stmts(destination, block, span, stmts, expr, safety_mode)
                 }

src/librustc_mir_build/build/expr/into.rs

@@ -135,30 +135,32 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // body, even when the exact code in the body cannot unwind
 
                 let loop_block = this.cfg.start_new_block();
+                let exit_block = this.cfg.start_new_block();
 
                 // Start the loop.
                 this.cfg.goto(block, source_info, loop_block);
 
-                this.in_breakable_scope(Some(loop_block), destination, expr_span, move |this| {
+                this.in_breakable_scope(Some(loop_block), exit_block, destination, move |this| {
                     // conduct the test, if necessary
                     let body_block = this.cfg.start_new_block();
+                    let diverge_cleanup = this.diverge_cleanup();
                     this.cfg.terminate(
                         loop_block,
                         source_info,
-                        TerminatorKind::FalseUnwind { real_target: body_block, unwind: None },
+                        TerminatorKind::FalseUnwind {
+                            real_target: body_block,
+                            unwind: Some(diverge_cleanup),
+                        },
                     );
-                    this.diverge_from(loop_block);
 
                     // The “return” value of the loop body must always be an unit. We therefore
                     // introduce a unit temporary as the destination for the loop body.
                     let tmp = this.get_unit_temp();
                     // Execute the body, branching back to the test.
                     let body_block_end = unpack!(this.into(tmp, body_block, body));
                     this.cfg.goto(body_block_end, source_info, loop_block);
-
-                    // Loops are only exited by `break` expressions.
-                    None
-                })
+                });
+                exit_block.unit()
             }
             ExprKind::Call { ty, fun, args, from_hir_call } => {
                 let intrinsic = match ty.kind {
@@ -200,6 +202,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         .collect();
 
                     let success = this.cfg.start_new_block();
+                    let cleanup = this.diverge_cleanup();
 
                     this.record_operands_moved(&args);
 
@@ -209,7 +212,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         TerminatorKind::Call {
                             func: fun,
                             args,
-                            cleanup: None,
+                            cleanup: Some(cleanup),
                             // FIXME(varkor): replace this with an uninhabitedness-based check.
                             // This requires getting access to the current module to call
                             // `tcx.is_ty_uninhabited_from`, which is currently tricky to do.
@@ -221,7 +224,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             from_hir_call,
                         },
                     );
-                    this.diverge_from(block);
                     success.unit()
                 }
             }
@@ -425,12 +427,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let scope = this.local_scope();
                 let value = unpack!(block = this.as_operand(block, scope, value));
                 let resume = this.cfg.start_new_block();
+                let cleanup = this.generator_drop_cleanup();
                 this.cfg.terminate(
                     block,
                     source_info,
-                    TerminatorKind::Yield { value, resume, resume_arg: destination, drop: None },
+                    TerminatorKind::Yield { value, resume, resume_arg: destination, drop: cleanup },
                 );
-                this.generator_drop_cleanup(block);
                 resume.unit()
             }
 

src/librustc_mir_build/build/matches/mod.rs

@@ -225,6 +225,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         outer_source_info: SourceInfo,
         fake_borrow_temps: Vec<(Place<'tcx>, Local)>,
     ) -> BlockAnd<()> {
+        let match_scope = self.scopes.topmost();
+
         let arm_end_blocks: Vec<_> = arm_candidates
             .into_iter()
             .map(|(arm, candidate)| {
@@ -245,7 +247,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let arm_block = this.bind_pattern(
                         outer_source_info,
                         candidate,
-                        arm.guard.as_ref(),
+                        arm.guard.as_ref().map(|g| (g, match_scope)),
                         &fake_borrow_temps,
                         scrutinee_span,
                         Some(arm.scope),
@@ -282,7 +284,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         &mut self,
         outer_source_info: SourceInfo,
         candidate: Candidate<'_, 'tcx>,
-        guard: Option<&Guard<'tcx>>,
+        guard: Option<(&Guard<'tcx>, region::Scope)>,
         fake_borrow_temps: &Vec<(Place<'tcx>, Local)>,
         scrutinee_span: Span,
         arm_scope: Option<region::Scope>,
@@ -1588,7 +1590,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         &mut self,
         candidate: Candidate<'pat, 'tcx>,
         parent_bindings: &[(Vec<Binding<'tcx>>, Vec<Ascription<'tcx>>)],
-        guard: Option<&Guard<'tcx>>,
+        guard: Option<(&Guard<'tcx>, region::Scope)>,
         fake_borrows: &Vec<(Place<'tcx>, Local)>,
         scrutinee_span: Span,
         schedule_drops: bool,
@@ -1700,7 +1702,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         //      the reference that we create for the arm.
         //    * So we eagerly create the reference for the arm and then take a
         //      reference to that.
-        if let Some(guard) = guard {
+        if let Some((guard, region_scope)) = guard {
             let tcx = self.hir.tcx();
             let bindings = parent_bindings
                 .iter()
@@ -1744,7 +1746,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 unreachable
             });
             let outside_scope = self.cfg.start_new_block();
-            self.exit_top_scope(otherwise_post_guard_block, outside_scope, source_info);
+            self.exit_scope(
+                source_info.span,
+                region_scope,
+                otherwise_post_guard_block,
+                outside_scope,
+            );
             self.false_edges(
                 outside_scope,
                 otherwise_block,

src/librustc_mir_build/build/matches/test.rs

@@ -423,6 +423,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let bool_ty = self.hir.bool_ty();
         let eq_result = self.temp(bool_ty, source_info.span);
         let eq_block = self.cfg.start_new_block();
+        let cleanup = self.diverge_cleanup();
         self.cfg.terminate(
             block,
             source_info,
@@ -439,12 +440,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     literal: method,
                 }),
                 args: vec![val, expect],
-                destination: Some((eq_result.clone(), eq_block)),
-                cleanup: None,
+                destination: Some((eq_result, eq_block)),
+                cleanup: Some(cleanup),
                 from_hir_call: false,
             },
         );
-        self.diverge_from(block);
 
         if let [success_block, fail_block] = *make_target_blocks(self) {
             // check the result

src/librustc_mir_build/build/mod.rs

@@ -327,6 +327,11 @@ struct Builder<'a, 'tcx> {
 
     var_debug_info: Vec<VarDebugInfo<'tcx>>,
 
+    /// Cached block with the `RESUME` terminator; this is created
+    /// when first set of cleanups are built.
+    cached_resume_block: Option<BasicBlock>,
+    /// Cached block with the `RETURN` terminator.
+    cached_return_block: Option<BasicBlock>,
     /// Cached block with the `UNREACHABLE` terminator.
     cached_unreachable_block: Option<BasicBlock>,
 }
@@ -585,34 +590,50 @@ where
         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::CallSite };
     let arg_scope =
         region::Scope { id: body.value.hir_id.local_id, data: region::ScopeData::Arguments };
+    let mut block = START_BLOCK;
     let source_info = builder.source_info(span);
     let call_site_s = (call_site_scope, source_info);
-    unpack!(builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {
-        let arg_scope_s = (arg_scope, source_info);
-        // Attribute epilogue to function's closing brace
-        let fn_end = span.shrink_to_hi();
-        let return_block =
-            unpack!(builder.in_breakable_scope(None, Place::return_place(), fn_end, |builder| {
-                Some(builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
-                    builder.args_and_body(
-                        START_BLOCK,
-                        fn_def_id.to_def_id(),
-                        &arguments,
-                        arg_scope,
-                        &body.value,
-                    )
-                }))
-            }));
-        let source_info = builder.source_info(fn_end);
-        builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
-        let should_abort = should_abort_on_panic(tcx, fn_def_id, abi);
-        builder.build_drop_trees(should_abort);
-        // Attribute any unreachable codepaths to the function's closing brace
-        if let Some(unreachable_block) = builder.cached_unreachable_block {
-            builder.cfg.terminate(unreachable_block, source_info, TerminatorKind::Unreachable);
-        }
-        return_block.unit()
-    }));
+    unpack!(
+        block = builder.in_scope(call_site_s, LintLevel::Inherited, |builder| {
+            if should_abort_on_panic(tcx, fn_def_id, abi) {
+                builder.schedule_abort();
+            }
+
+            let arg_scope_s = (arg_scope, source_info);
+            // `return_block` is called when we evaluate a `return` expression, so
+            // we just use `START_BLOCK` here.
+            unpack!(
+                block = builder.in_breakable_scope(
+                    None,
+                    START_BLOCK,
+                    Place::return_place(),
+                    |builder| {
+                        builder.in_scope(arg_scope_s, LintLevel::Inherited, |builder| {
+                            builder.args_and_body(
+                                block,
+                                fn_def_id.to_def_id(),
+                                &arguments,
+                                arg_scope,
+                                &body.value,
+                            )
+                        })
+                    },
+                )
+            );
+            // Attribute epilogue to function's closing brace
+            let fn_end = span.shrink_to_hi();
+            let source_info = builder.source_info(fn_end);
+            let return_block = builder.return_block();
+            builder.cfg.goto(block, source_info, return_block);
+            builder.cfg.terminate(return_block, source_info, TerminatorKind::Return);
+            // Attribute any unreachable codepaths to the function's closing brace
+            if let Some(unreachable_block) = builder.cached_unreachable_block {
+                builder.cfg.terminate(unreachable_block, source_info, TerminatorKind::Unreachable);
+            }
+            return_block.unit()
+        })
+    );
+    assert_eq!(block, builder.return_block());
 
     let spread_arg = if abi == Abi::RustCall {
         // RustCall pseudo-ABI untuples the last argument.
@@ -646,7 +667,8 @@ fn construct_const<'a, 'tcx>(
     let source_info = builder.source_info(span);
     builder.cfg.terminate(block, source_info, TerminatorKind::Return);
 
-    builder.build_drop_trees(false);
+    // Constants can't `return` so a return block should not be created.
+    assert_eq!(builder.cached_return_block, None);
 
     // Constants may be match expressions in which case an unreachable block may
     // be created, so terminate it properly.
@@ -713,7 +735,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             fn_span: span,
             arg_count,
             generator_kind,
-            scopes: scope::Scopes::new(),
+            scopes: Default::default(),
             block_context: BlockContext::new(),
             source_scopes: IndexVec::new(),
             source_scope: OUTERMOST_SOURCE_SCOPE,
@@ -726,6 +748,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             var_indices: Default::default(),
             unit_temp: None,
             var_debug_info: vec![],
+            cached_resume_block: None,
+            cached_return_block: None,
             cached_unreachable_block: None,
         };
 
@@ -957,6 +981,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
         }
     }
+
+    fn return_block(&mut self) -> BasicBlock {
+        match self.cached_return_block {
+            Some(rb) => rb,
+            None => {
+                let rb = self.cfg.start_new_block();
+                self.cached_return_block = Some(rb);
+                rb
+            }
+        }
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////