how much do the tricolor dfs + sccs cost?

Author: lqd

compiler/rustc_borrowck/src/lib.rs

@@ -438,13 +438,24 @@ fn do_mir_borrowck<'tcx>(
 
     let (mut flow_analysis, flow_entry_states) =
         get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
-    visit_results(
-        body,
-        traversal::reverse_postorder(body).map(|(bb, _)| bb),
-        &mut flow_analysis,
-        &flow_entry_states,
-        &mut mbcx,
-    );
+    if body.basic_blocks.is_cfg_cyclic() {
+        let _sccs = body.basic_blocks.sccs();
+        visit_results(
+            body,
+            traversal::reverse_postorder(body).map(|(bb, _)| bb),
+            &mut flow_analysis,
+            &flow_entry_states,
+            &mut mbcx,
+        );
+    } else {
+        visit_results(
+            body,
+            traversal::reverse_postorder(body).map(|(bb, _)| bb),
+            &mut flow_analysis,
+            &flow_entry_states,
+            &mut mbcx,
+        );
+    }
 
     mbcx.report_move_errors();
 

compiler/rustc_mir_dataflow/src/framework/mod.rs

@@ -240,14 +240,7 @@ pub trait Analysis<'tcx> {
         Self: Sized,
         Self::Domain: DebugWithContext<Self>,
     {
-        // Computing dataflow over the SCCs is only supported in forward analyses. It's also
-        // unnecessary to use it on acyclic graphs, as the condensation graph is of course the same
-        // as the CFG itself.
-        if Self::Direction::IS_BACKWARD || !body.basic_blocks.is_cfg_cyclic() {
-            self.iterate_to_fixpoint_per_block(tcx, body, pass_name)
-        } else {
-            self.iterate_to_fixpoint_per_scc(tcx, body, pass_name)
-        }
+        self.iterate_to_fixpoint_per_block(tcx, body, pass_name)
     }
 
     /* Extension methods */