cleanup cfg after optimization

Author: simonvandel

compiler/rustc_mir/src/transform/remove_unneeded_drops.rs

@@ -6,6 +6,8 @@ use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 
+use super::simplify::simplify_cfg;
+
 pub struct RemoveUnneededDrops;
 
 impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
@@ -18,11 +20,18 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
             def_id: source.def_id().expect_local(),
         };
         opt_finder.visit_body(body);
+        let should_simplify = !opt_finder.optimizations.is_empty();
         for (loc, target) in opt_finder.optimizations {
             let terminator = body.basic_blocks_mut()[loc.block].terminator_mut();
             debug!("SUCCESS: replacing `drop` with goto({:?})", target);
             terminator.kind = TerminatorKind::Goto { target };
         }
+
+        // if we applied optimizations, we potentially have some cfg to cleanup to
+        // make it easier for further passes
+        if should_simplify {
+            simplify_cfg(body);
+        }
     }
 }
 

src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff

@@ -16,10 +16,9 @@
           _3 = _1;                         // scope 0 at $DIR/remove_unneeded_drops.rs:3:10: 3:11
           _2 = const ();                   // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
 -         drop(_3) -> bb1;                 // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
-+         goto -> bb1;                     // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
-      }
-  
-      bb1: {
+-     }
+- 
+-     bb1: {
           StorageDead(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:3:11: 3:12
           StorageDead(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:3:12: 3:13
           _0 = const ();                   // scope 0 at $DIR/remove_unneeded_drops.rs:2:17: 4:2

src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff

@@ -16,10 +16,9 @@
           _3 = _1;                         // scope 0 at $DIR/remove_unneeded_drops.rs:13:10: 13:11
           _2 = const ();                   // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
 -         drop(_3) -> bb1;                 // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
-+         goto -> bb1;                     // scope 1 at $SRC_DIR/core/src/mem/mod.rs:LL:COL
-      }
-  
-      bb1: {
+-     }
+- 
+-     bb1: {
           StorageDead(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:13:11: 13:12
           StorageDead(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:13:12: 13:13
           _0 = const ();                   // scope 0 at $DIR/remove_unneeded_drops.rs:12:36: 14:2