stacked borrows tests: add those that fail under TB

Author: RalfJung

src/tools/miri/tests/fail/tree_borrows/write-during-2phase.rs

@@ -8,8 +8,8 @@
 
 struct Foo(u64);
 impl Foo {
-    #[rustfmt::skip] // rustfmt is wrong about which line contains an error
-    fn add(&mut self, n: u64) -> u64 { //~ ERROR: /reborrow through .* is forbidden/
+    fn add(&mut self, n: u64) -> u64 {
+        //~^ ERROR: /reborrow through .* is forbidden/
         self.0 + n
     }
 }

src/tools/miri/tests/pass/stacked-borrows/2phase.rs

@@ -1,3 +1,6 @@
+// FIXME: this miscompiles with optimizations, see <https://github.com/rust-lang/rust/issues/132898>.
+//@compile-flags: -Zmir-opt-level=0
+
 trait S: Sized {
     fn tpb(&mut self, _s: Self) {}
 }
@@ -75,6 +78,25 @@ fn with_interior_mutability() {
     });
 }
 
+// This one really shouldn't be accepted, but since we treat 2phase as raw, we do accept it.
+// Tree Borrows rejects it.
+fn aliasing_violation() {
+    struct Foo(u64);
+    impl Foo {
+        fn add(&mut self, n: u64) -> u64 {
+            self.0 + n
+        }
+    }
+
+    let mut f = Foo(0);
+    let alias = &mut f.0 as *mut u64;
+    let res = f.add(unsafe {
+        *alias = 42;
+        0
+    });
+    assert_eq!(res, 42);
+}
+
 fn main() {
     two_phase1();
     two_phase2();
@@ -84,4 +106,5 @@ fn main() {
     with_interior_mutability();
     two_phase_overlapping1();
     two_phase_overlapping2();
+    aliasing_violation();
 }

src/tools/miri/tests/pass/stacked-borrows/stacked-borrows.rs

@@ -8,6 +8,7 @@ fn main() {
     mut_raw_then_mut_shr();
     mut_shr_then_mut_raw();
     mut_raw_mut();
+    mut_raw_mut2();
     partially_invalidate_mut();
     drop_after_sharing();
     // direct_mut_to_const_raw();
@@ -96,6 +97,18 @@ fn mut_raw_mut() {
     assert_eq!(x, 4);
 }
 
+// A variant of `mut_raw_mut` that does *not* get accepted by Tree Borrows.
+// It's kind of an accident that we accept it in Stacked Borrows...
+fn mut_raw_mut2() {
+    unsafe {
+        let mut root = 0;
+        let to = &mut root as *mut i32;
+        *to = 0;
+        let _val = root;
+        *to = 0;
+    }
+}
+
 fn partially_invalidate_mut() {
     let data = &mut (0u8, 0u8);
     let reborrow = &mut *data as *mut (u8, u8);