remove_dead_drops: run simplify_cfg if anything changed

Author: tmandry

compiler/rustc_mir_transform/src/remove_dead_drops.rs

@@ -4,6 +4,8 @@ use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::{LookupResult, MoveData};
 use rustc_mir_dataflow::{Analysis, MaybeReachable};
 
+use super::simplify::simplify_cfg;
+
 pub(crate) struct RemoveDeadDrops;
 
 impl<'tcx> crate::MirPass<'tcx> for RemoveDeadDrops {
@@ -42,10 +44,15 @@ impl<'tcx> crate::MirPass<'tcx> for RemoveDeadDrops {
             }
         }
 
-        for (block, target) in dead_drops {
-            if let Some(terminator) = &mut body.basic_blocks.as_mut()[block].terminator {
-                terminator.kind = TerminatorKind::Goto { target };
+        if !dead_drops.is_empty() {
+            for (block, target) in dead_drops {
+                if let Some(terminator) = &mut body.basic_blocks.as_mut()[block].terminator {
+                    terminator.kind = TerminatorKind::Goto { target };
+                }
             }
+
+            // Removing drop terminators may simplify the CFG, so run cleanup.
+            simplify_cfg(tcx, body);
         }
     }
 }

tests/mir-opt/building/uniform_array_move_out.move_out_by_subslice.CleanupPostBorrowck.after.mir

@@ -16,53 +16,45 @@ fn move_out_by_subslice() -> () {
     bb0: {
         StorageLive(_1);
         StorageLive(_2);
-        _2 = Box::<i32>::new(const 1_i32) -> [return: bb1, unwind: bb9];
+        _2 = Box::<i32>::new(const 1_i32) -> [return: bb1, unwind: bb7];
     }
 
     bb1: {
         StorageLive(_3);
-        _3 = Box::<i32>::new(const 2_i32) -> [return: bb2, unwind: bb8];
+        _3 = Box::<i32>::new(const 2_i32) -> [return: bb2, unwind: bb6];
     }
 
     bb2: {
         _1 = [move _2, move _3];
-        goto -> bb3;
-    }
-
-    bb3: {
         StorageDead(_3);
-        goto -> bb4;
-    }
-
-    bb4: {
         StorageDead(_2);
         nop;
         PlaceMention(_1);
         StorageLive(_4);
         _4 = move _1[0..2];
         _0 = const ();
-        drop(_4) -> [return: bb5, unwind: bb7];
+        drop(_4) -> [return: bb3, unwind: bb5];
     }
 
-    bb5: {
+    bb3: {
         StorageDead(_4);
-        drop(_1) -> [return: bb6, unwind: bb9];
+        drop(_1) -> [return: bb4, unwind: bb7];
     }
 
-    bb6: {
+    bb4: {
         StorageDead(_1);
         return;
     }
 
-    bb7 (cleanup): {
-        drop(_1) -> [return: bb9, unwind terminate(cleanup)];
+    bb5 (cleanup): {
+        drop(_1) -> [return: bb7, unwind terminate(cleanup)];
     }
 
-    bb8 (cleanup): {
-        drop(_2) -> [return: bb9, unwind terminate(cleanup)];
+    bb6 (cleanup): {
+        drop(_2) -> [return: bb7, unwind terminate(cleanup)];
     }
 
-    bb9 (cleanup): {
+    bb7 (cleanup): {
         resume;
     }
 }

tests/mir-opt/building/uniform_array_move_out.move_out_from_end.CleanupPostBorrowck.after.mir

@@ -16,53 +16,45 @@ fn move_out_from_end() -> () {
     bb0: {
         StorageLive(_1);
         StorageLive(_2);
-        _2 = Box::<i32>::new(const 1_i32) -> [return: bb1, unwind: bb9];
+        _2 = Box::<i32>::new(const 1_i32) -> [return: bb1, unwind: bb7];
     }
 
     bb1: {
         StorageLive(_3);
-        _3 = Box::<i32>::new(const 2_i32) -> [return: bb2, unwind: bb8];
+        _3 = Box::<i32>::new(const 2_i32) -> [return: bb2, unwind: bb6];
     }
 
     bb2: {
         _1 = [move _2, move _3];
-        goto -> bb3;
-    }
-
-    bb3: {
         StorageDead(_3);
-        goto -> bb4;
-    }
-
-    bb4: {
         StorageDead(_2);
         nop;
         PlaceMention(_1);
         StorageLive(_4);
         _4 = move _1[1 of 2];
         _0 = const ();
-        drop(_4) -> [return: bb5, unwind: bb7];
+        drop(_4) -> [return: bb3, unwind: bb5];
     }
 
-    bb5: {
+    bb3: {
         StorageDead(_4);
-        drop(_1) -> [return: bb6, unwind: bb9];
+        drop(_1) -> [return: bb4, unwind: bb7];
     }
 
-    bb6: {
+    bb4: {
         StorageDead(_1);
         return;
     }
 
-    bb7 (cleanup): {
-        drop(_1) -> [return: bb9, unwind terminate(cleanup)];
+    bb5 (cleanup): {
+        drop(_1) -> [return: bb7, unwind terminate(cleanup)];
     }
 
-    bb8 (cleanup): {
-        drop(_2) -> [return: bb9, unwind terminate(cleanup)];
+    bb6 (cleanup): {
+        drop(_2) -> [return: bb7, unwind terminate(cleanup)];
     }
 
-    bb9 (cleanup): {
+    bb7 (cleanup): {
         resume;
     }
 }

tests/mir-opt/building/write_box_via_move.box_new.CleanupPostBorrowck.after.mir

@@ -13,7 +13,7 @@ fn box_new(_1: T) -> Box<[T; 1024]> {
 
     bb0: {
         StorageLive(_2);
-        _2 = Box::<[T; 1024]>::new_uninit() -> [return: bb1, unwind: bb7];
+        _2 = Box::<[T; 1024]>::new_uninit() -> [return: bb1, unwind: bb4];
     }
 
     bb1: {
@@ -26,33 +26,21 @@ fn box_new(_1: T) -> Box<[T; 1024]> {
         ((((*_4).1: std::mem::ManuallyDrop<[T; 1024]>).0: std::mem::MaybeDangling<[T; 1024]>).0: [T; 1024]) = [move _5; 1024];
         StorageDead(_5);
         _3 = move _4;
-        goto -> bb2;
-    }
-
-    bb2: {
         StorageDead(_4);
-        _0 = Box::<MaybeUninit<[T; 1024]>>::assume_init(move _3) -> [return: bb3, unwind: bb5];
+        _0 = Box::<MaybeUninit<[T; 1024]>>::assume_init(move _3) -> [return: bb2, unwind: bb3];
     }
 
-    bb3: {
+    bb2: {
         StorageDead(_3);
-        goto -> bb4;
-    }
-
-    bb4: {
         StorageDead(_2);
         return;
     }
 
-    bb5 (cleanup): {
-        drop(_3) -> [return: bb6, unwind terminate(cleanup)];
-    }
-
-    bb6 (cleanup): {
-        goto -> bb7;
+    bb3 (cleanup): {
+        drop(_3) -> [return: bb4, unwind terminate(cleanup)];
     }
 
-    bb7 (cleanup): {
+    bb4 (cleanup): {
         resume;
     }
 }

tests/mir-opt/building/write_box_via_move.vec_macro.CleanupPostBorrowck.after.mir

@@ -8,30 +8,26 @@ fn vec_macro() -> Vec<i32> {
     bb0: {
         StorageLive(_1);
         StorageLive(_2);
-        _2 = Box::<[i32; 8]>::new_uninit() -> [return: bb1, unwind: bb5];
+        _2 = Box::<[i32; 8]>::new_uninit() -> [return: bb1, unwind: bb4];
     }
 
     bb1: {
         ((((*_2).1: std::mem::ManuallyDrop<[i32; 8]>).0: std::mem::MaybeDangling<[i32; 8]>).0: [i32; 8]) = [const 0_i32, const 1_i32, const 2_i32, const 3_i32, const 4_i32, const 5_i32, const 6_i32, const 7_i32];
         _1 = move _2;
-        goto -> bb2;
-    }
-
-    bb2: {
         StorageDead(_2);
-        _0 = std::boxed::box_assume_init_into_vec_unsafe::<i32, 8>(move _1) -> [return: bb3, unwind: bb4];
+        _0 = std::boxed::box_assume_init_into_vec_unsafe::<i32, 8>(move _1) -> [return: bb2, unwind: bb3];
     }
 
-    bb3: {
+    bb2: {
         StorageDead(_1);
         return;
     }
 
-    bb4 (cleanup): {
-        drop(_1) -> [return: bb5, unwind terminate(cleanup)];
+    bb3 (cleanup): {
+        drop(_1) -> [return: bb4, unwind terminate(cleanup)];
     }
 
-    bb5 (cleanup): {
+    bb4 (cleanup): {
         resume;
     }
 }

tests/mir-opt/building/write_via_move.box_new.CleanupPostBorrowck.after.mir

@@ -20,7 +20,7 @@ fn box_new(_1: T) -> Box<[T; 1024]> {
 
     bb0: {
         StorageLive(_2);
-        _2 = Box::<[T; 1024]>::new_uninit() -> [return: bb1, unwind: bb7];
+        _2 = Box::<[T; 1024]>::new_uninit() -> [return: bb1, unwind: bb5];
     }
 
     bb1: {
@@ -30,7 +30,7 @@ fn box_new(_1: T) -> Box<[T; 1024]> {
         StorageLive(_5);
         _5 = &mut (*_2);
         _4 = &mut (*_5);
-        _3 = MaybeUninit::<[T; 1024]>::as_mut_ptr(move _4) -> [return: bb2, unwind: bb6];
+        _3 = MaybeUninit::<[T; 1024]>::as_mut_ptr(move _4) -> [return: bb2, unwind: bb4];
     }
 
     bb2: {
@@ -48,29 +48,21 @@ fn box_new(_1: T) -> Box<[T; 1024]> {
         StorageDead(_6);
         StorageLive(_9);
         _9 = move _2;
-        _0 = Box::<MaybeUninit<[T; 1024]>>::assume_init(move _9) -> [return: bb3, unwind: bb5];
+        _0 = Box::<MaybeUninit<[T; 1024]>>::assume_init(move _9) -> [return: bb3, unwind: bb4];
     }
 
     bb3: {
         StorageDead(_9);
         StorageDead(_3);
-        goto -> bb4;
-    }
-
-    bb4: {
         StorageDead(_2);
         return;
     }
 
-    bb5 (cleanup): {
-        goto -> bb6;
-    }
-
-    bb6 (cleanup): {
-        drop(_2) -> [return: bb7, unwind terminate(cleanup)];
+    bb4 (cleanup): {
+        drop(_2) -> [return: bb5, unwind terminate(cleanup)];
     }
 
-    bb7 (cleanup): {
+    bb5 (cleanup): {
         resume;
     }
 }