Use PlaceMention for match scrutinees.

Author: cjgillot

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -223,6 +223,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let fake_borrow_temps = self.lower_match_tree(
             block,
             scrutinee_span,
+            &scrutinee_place,
             match_start_span,
             match_has_guard,
             &mut candidates,
@@ -246,26 +247,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         scrutinee_span: Span,
     ) -> BlockAnd<PlaceBuilder<'tcx>> {
         let scrutinee_place_builder = unpack!(block = self.as_place_builder(block, scrutinee));
-        // Matching on a `scrutinee_place` with an uninhabited type doesn't
-        // generate any memory reads by itself, and so if the place "expression"
-        // contains unsafe operations like raw pointer dereferences or union
-        // field projections, we wouldn't know to require an `unsafe` block
-        // around a `match` equivalent to `std::intrinsics::unreachable()`.
-        // See issue #47412 for this hole being discovered in the wild.
-        //
-        // HACK(eddyb) Work around the above issue by adding a dummy inspection
-        // of `scrutinee_place`, specifically by applying `ReadForMatch`.
-        //
-        // NOTE: ReadForMatch also checks that the scrutinee is initialized.
-        // This is currently needed to not allow matching on an uninitialized,
-        // uninhabited value. If we get never patterns, those will check that
-        // the place is initialized, and so this read would only be used to
-        // check safety.
-        let cause_matched_place = FakeReadCause::ForMatchedPlace(None);
-        let source_info = self.source_info(scrutinee_span);
-
         if let Some(scrutinee_place) = scrutinee_place_builder.try_to_place(self) {
-            self.cfg.push_fake_read(block, source_info, cause_matched_place, scrutinee_place);
+            let source_info = self.source_info(scrutinee_span);
+            self.cfg.push_place_mention(block, source_info, scrutinee_place);
         }
 
         block.and(scrutinee_place_builder)
@@ -304,6 +288,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         &mut self,
         block: BasicBlock,
         scrutinee_span: Span,
+        scrutinee_place_builder: &PlaceBuilder<'tcx>,
         match_start_span: Span,
         match_has_guard: bool,
         candidates: &mut [&mut Candidate<'pat, 'tcx>],
@@ -331,6 +316,33 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // otherwise block. Match checking will ensure this is actually
             // unreachable.
             let source_info = self.source_info(scrutinee_span);
+
+            // Matching on a `scrutinee_place` with an uninhabited type doesn't
+            // generate any memory reads by itself, and so if the place "expression"
+            // contains unsafe operations like raw pointer dereferences or union
+            // field projections, we wouldn't know to require an `unsafe` block
+            // around a `match` equivalent to `std::intrinsics::unreachable()`.
+            // See issue #47412 for this hole being discovered in the wild.
+            //
+            // HACK(eddyb) Work around the above issue by adding a dummy inspection
+            // of `scrutinee_place`, specifically by applying `ReadForMatch`.
+            //
+            // NOTE: ReadForMatch also checks that the scrutinee is initialized.
+            // This is currently needed to not allow matching on an uninitialized,
+            // uninhabited value. If we get never patterns, those will check that
+            // the place is initialized, and so this read would only be used to
+            // check safety.
+            let cause_matched_place = FakeReadCause::ForMatchedPlace(None);
+
+            if let Some(scrutinee_place) = scrutinee_place_builder.try_to_place(self) {
+                self.cfg.push_fake_read(
+                    otherwise_block,
+                    source_info,
+                    cause_matched_place,
+                    scrutinee_place,
+                );
+            }
+
             self.cfg.terminate(otherwise_block, source_info, TerminatorKind::Unreachable);
         }
 
@@ -599,13 +611,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
 
             _ => {
-                let place_builder = unpack!(block = self.as_place_builder(block, initializer));
-
-                if let Some(place) = place_builder.try_to_place(self) {
-                    let source_info = self.source_info(initializer.span);
-                    self.cfg.push_place_mention(block, source_info, place);
-                }
-
+                let place_builder =
+                    unpack!(block = self.lower_scrutinee(block, initializer, initializer.span));
                 self.place_into_pattern(block, &irrefutable_pat, place_builder, true)
             }
         }
@@ -622,6 +629,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let fake_borrow_temps = self.lower_match_tree(
             block,
             irrefutable_pat.span,
+            &initializer,
             irrefutable_pat.span,
             false,
             &mut [&mut candidate],
@@ -1837,6 +1845,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let fake_borrow_temps = self.lower_match_tree(
             block,
             pat.span,
+            &expr_place_builder,
             pat.span,
             false,
             &mut [&mut guard_candidate, &mut otherwise_candidate],
@@ -2338,6 +2347,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             let fake_borrow_temps = this.lower_match_tree(
                 block,
                 initializer_span,
+                &scrutinee,
                 pattern.span,
                 false,
                 &mut [&mut candidate, &mut wildcard],

tests/mir-opt/building/async_await.b-{closure#0}.coroutine_resume.0.mir

@@ -127,6 +127,7 @@ fn b::{closure#0}(_1: Pin<&mut {async fn body@$DIR/async_await.rs:15:18: 18:2}>,
 
     bb3: {
         StorageDead(_5);
+        PlaceMention(_4);
         nop;
         (((*(_1.0: &mut {async fn body@$DIR/async_await.rs:15:18: 18:2})) as variant#3).0: {async fn body@$DIR/async_await.rs:12:14: 12:16}) = move _4;
         goto -> bb4;
@@ -162,6 +163,7 @@ fn b::{closure#0}(_1: Pin<&mut {async fn body@$DIR/async_await.rs:15:18: 18:2}>,
     bb7: {
         StorageDead(_13);
         StorageDead(_10);
+        PlaceMention(_9);
         _16 = discriminant(_9);
         switchInt(move _16) -> [0: bb10, 1: bb8, otherwise: bb9];
     }
@@ -223,6 +225,7 @@ fn b::{closure#0}(_1: Pin<&mut {async fn body@$DIR/async_await.rs:15:18: 18:2}>,
 
     bb15: {
         StorageDead(_22);
+        PlaceMention(_21);
         nop;
         (((*(_1.0: &mut {async fn body@$DIR/async_await.rs:15:18: 18:2})) as variant#4).0: {async fn body@$DIR/async_await.rs:12:14: 12:16}) = move _21;
         goto -> bb16;
@@ -258,6 +261,7 @@ fn b::{closure#0}(_1: Pin<&mut {async fn body@$DIR/async_await.rs:15:18: 18:2}>,
     bb19: {
         StorageDead(_29);
         StorageDead(_26);
+        PlaceMention(_25);
         _32 = discriminant(_25);
         switchInt(move _32) -> [0: bb21, 1: bb20, otherwise: bb9];
     }

tests/mir-opt/building/issue_101867.main.built.after.mir

@@ -25,7 +25,7 @@ fn main() -> () {
         FakeRead(ForLet(None), _1);
         AscribeUserType(_1, o, UserTypeProjection { base: UserType(1), projs: [] });
         StorageLive(_5);
-        FakeRead(ForMatchedPlace(None), _1);
+        PlaceMention(_1);
         _6 = discriminant(_1);
         switchInt(move _6) -> [1: bb4, otherwise: bb3];
     }

tests/mir-opt/building/issue_49232.main.built.after.mir

@@ -24,7 +24,7 @@ fn main() -> () {
         StorageLive(_2);
         StorageLive(_3);
         _3 = const true;
-        FakeRead(ForMatchedPlace(None), _3);
+        PlaceMention(_3);
         switchInt(_3) -> [0: bb3, otherwise: bb4];
     }
 

tests/mir-opt/building/logical_or_in_conditional.test_complex.built.after.mir

@@ -23,7 +23,7 @@ fn test_complex() -> () {
     }
 
     bb1: {
-        FakeRead(ForMatchedPlace(None), _2);
+        PlaceMention(_2);
         _3 = discriminant(_2);
         switchInt(move _3) -> [0: bb2, otherwise: bb3];
     }
@@ -151,7 +151,7 @@ fn test_complex() -> () {
     }
 
     bb25: {
-        FakeRead(ForMatchedPlace(None), _12);
+        PlaceMention(_12);
         _13 = discriminant(_12);
         switchInt(move _13) -> [1: bb27, otherwise: bb26];
     }

tests/mir-opt/building/match_false_edges.full_tested_match.built.after.mir

@@ -26,7 +26,7 @@ fn full_tested_match() -> () {
         StorageLive(_1);
         StorageLive(_2);
         _2 = Option::<i32>::Some(const 42_i32);
-        FakeRead(ForMatchedPlace(None), _2);
+        PlaceMention(_2);
         _3 = discriminant(_2);
         switchInt(move _3) -> [0: bb1, 1: bb2, otherwise: bb4];
     }
@@ -45,6 +45,7 @@ fn full_tested_match() -> () {
     }
 
     bb4: {
+        FakeRead(ForMatchedPlace(None), _2);
         unreachable;
     }
 

tests/mir-opt/building/match_false_edges.full_tested_match2.built.after.mir

@@ -26,7 +26,7 @@ fn full_tested_match2() -> () {
         StorageLive(_1);
         StorageLive(_2);
         _2 = Option::<i32>::Some(const 42_i32);
-        FakeRead(ForMatchedPlace(None), _2);
+        PlaceMention(_2);
         _3 = discriminant(_2);
         switchInt(move _3) -> [0: bb1, 1: bb2, otherwise: bb4];
     }
@@ -51,6 +51,7 @@ fn full_tested_match2() -> () {
     }
 
     bb4: {
+        FakeRead(ForMatchedPlace(None), _2);
         unreachable;
     }
 

tests/mir-opt/building/match_false_edges.main.built.after.mir

@@ -37,7 +37,7 @@ fn main() -> () {
         StorageLive(_1);
         StorageLive(_2);
         _2 = Option::<i32>::Some(const 1_i32);
-        FakeRead(ForMatchedPlace(None), _2);
+        PlaceMention(_2);
         _4 = discriminant(_2);
         switchInt(move _4) -> [1: bb2, otherwise: bb1];
     }

tests/mir-opt/building/simple_match.match_bool.built.after.mir

@@ -5,7 +5,7 @@ fn match_bool(_1: bool) -> usize {
     let mut _0: usize;
 
     bb0: {
-        FakeRead(ForMatchedPlace(None), _1);
+        PlaceMention(_1);
         switchInt(_1) -> [0: bb2, otherwise: bb1];
     }
 

tests/mir-opt/const_prop/transmute.unreachable_box.ConstProp.32bit.diff

@@ -4,6 +4,7 @@
   fn unreachable_box() -> ! {
       let mut _0: !;
       let _1: std::boxed::Box<Never>;
+      let mut _2: *const Never;
       scope 1 {
           debug x => _1;
       }
@@ -13,7 +14,9 @@
       bb0: {
           StorageLive(_1);
 -         _1 = const 1_usize as std::boxed::Box<Never> (Transmute);
+-         _2 = (((_1.0: std::ptr::Unique<Never>).0: std::ptr::NonNull<Never>).0: *const Never);
 +         _1 = const Box::<Never>(Unique::<Never> {{ pointer: NonNull::<Never> {{ pointer: {0x1 as *const Never} }}, _marker: PhantomData::<Never> }}, std::alloc::Global);
++         _2 = const {0x1 as *const Never};
           unreachable;
       }
   }