1 files changed, 280 insertions, 0 deletions
diff --git a/src/tools/miri/tests/pass/tree-borrows/tree-borrows.rs b/src/tools/miri/tests/pass/tree-borrows/tree-borrows.rs
new file mode 100644
index 00000000000..aa6f7078890
--- /dev/null
+++ b/src/tools/miri/tests/pass/tree-borrows/tree-borrows.rs
@@ -0,0 +1,280 @@
+//@compile-flags: -Zmiri-tree-borrows
+#![feature(allocator_api)]
+
+use std::mem;
+use std::ptr;
+
+fn main() {
+    aliasing_read_only_mutable_refs();
+    string_as_mut_ptr();
+
+    // Stacked Borrows tests
+    read_does_not_invalidate1();
+    read_does_not_invalidate2();
+    mut_raw_then_mut_shr();
+    mut_shr_then_mut_raw();
+    mut_raw_mut();
+    partially_invalidate_mut();
+    drop_after_sharing();
+    direct_mut_to_const_raw();
+    two_raw();
+    shr_and_raw();
+    disjoint_mutable_subborrows();
+    raw_ref_to_part();
+    array_casts();
+    mut_below_shr();
+    wide_raw_ptr_in_tuple();
+    not_unpin_not_protected();
+}
+
+// Tree Borrows has no issue with several mutable references existing
+// at the same time, as long as they are used only immutably.
+// I.e. multiple Reserved can coexist.
+pub fn aliasing_read_only_mutable_refs() {
+    unsafe {
+        let base = &mut 42u64;
+        let r1 = &mut *(base as *mut u64);
+        let r2 = &mut *(base as *mut u64);
+        let _l = *r1;
+        let _l = *r2;
+    }
+}
+
+pub fn string_as_mut_ptr() {
+    // This errors in Stacked Borrows since as_mut_ptr restricts the provenance,
+    // but with Tree Borrows it should work.
+    unsafe {
+        let mut s = String::from("hello");
+        s.reserve(1); // make the `str` that `s` derefs to not cover the entire `s`.
+
+        // Prevent automatically dropping the String's data
+        let mut s = mem::ManuallyDrop::new(s);
+
+        let ptr = s.as_mut_ptr();
+        let len = s.len();
+        let capacity = s.capacity();
+
+        let s = String::from_raw_parts(ptr, len, capacity);
+
+        assert_eq!(String::from("hello"), s);
+    }
+}
+
+// ----- The tests below were taken from Stacked Borrows ----
+
+// Make sure that reading from an `&mut` does, like reborrowing to `&`,
+// NOT invalidate other reborrows.
+fn read_does_not_invalidate1() {
+    fn foo(x: &mut (i32, i32)) -> &i32 {
+        let xraw = x as *mut (i32, i32);
+        let ret = unsafe { &(*xraw).1 };
+        let _val = x.1; // we just read, this does NOT invalidate the reborrows.
+        ret
+    }
+    assert_eq!(*foo(&mut (1, 2)), 2);
+}
+// Same as above, but this time we first create a raw, then read from `&mut`
+// and then freeze from the raw.
+fn read_does_not_invalidate2() {
+    fn foo(x: &mut (i32, i32)) -> &i32 {
+        let xraw = x as *mut (i32, i32);
+        let _val = x.1; // we just read, this does NOT invalidate the raw reborrow.
+        let ret = unsafe { &(*xraw).1 };
+        ret
+    }
+    assert_eq!(*foo(&mut (1, 2)), 2);
+}
+
+// Escape a mut to raw, then share the same mut and use the share, then the raw.
+// That should work.
+fn mut_raw_then_mut_shr() {
+    let mut x = 2;
+    let xref = &mut x;
+    let xraw = &mut *xref as *mut _;
+    let xshr = &*xref;
+    assert_eq!(*xshr, 2);
+    unsafe {
+        *xraw = 4;
+    }
+    assert_eq!(x, 4);
+}
+
+// Create first a shared reference and then a raw pointer from a `&mut`
+// should permit mutation through that raw pointer.
+fn mut_shr_then_mut_raw() {
+    let xref = &mut 2;
+    let _xshr = &*xref;
+    let xraw = xref as *mut _;
+    unsafe {
+        *xraw = 3;
+    }
+    assert_eq!(*xref, 3);
+}
+
+// Ensure that if we derive from a mut a raw, and then from that a mut,
+// and then read through the original mut, that does not invalidate the raw.
+// This shows that the read-exception for `&mut` applies even if the `Shr` item
+// on the stack is not at the top.
+fn mut_raw_mut() {
+    let mut x = 2;
+    {
+        let xref1 = &mut x;
+        let xraw = xref1 as *mut _;
+        let _xref2 = unsafe { &mut *xraw };
+        let _val = *xref1;
+        unsafe {
+            *xraw = 4;
+        }
+        // we can now use both xraw and xref1, for reading
+        assert_eq!(*xref1, 4);
+        assert_eq!(unsafe { *xraw }, 4);
+        assert_eq!(*xref1, 4);
+        assert_eq!(unsafe { *xraw }, 4);
+        // we cannot use xref2; see `compile-fail/stacked-borrows/illegal_read4.rs`
+    }
+    assert_eq!(x, 4);
+}
+
+fn partially_invalidate_mut() {
+    let data = &mut (0u8, 0u8);
+    let reborrow = &mut *data as *mut (u8, u8);
+    let shard = unsafe { &mut (*reborrow).0 };
+    data.1 += 1; // the deref overlaps with `shard`, but that is ok; the access does not overlap.
+    *shard += 1; // so we can still use `shard`.
+    assert_eq!(*data, (1, 1));
+}
+
+// Make sure that we can handle the situation where a location is frozen when being dropped.
+fn drop_after_sharing() {
+    let x = String::from("hello!");
+    let _len = x.len();
+}
+
+// Make sure that coercing &mut T to *const T produces a writeable pointer.
+fn direct_mut_to_const_raw() {
+    // TODO: This is currently disabled, waiting on a decision on <https://github.com/rust-lang/rust/issues/56604>
+    /*let x = &mut 0;
+    let y: *const i32 = x;
+    unsafe { *(y as *mut i32) = 1; }
+    assert_eq!(*x, 1);
+    */
+}
+
+// Make sure that we can create two raw pointers from a mutable reference and use them both.
+fn two_raw() {
+    unsafe {
+        let x = &mut 0;
+        let y1 = x as *mut _;
+        let y2 = x as *mut _;
+        *y1 += 2;
+        *y2 += 1;
+    }
+}
+
+// Make sure that creating a *mut does not invalidate existing shared references.
+fn shr_and_raw() {
+    unsafe {
+        let x = &mut 0;
+        let y1: &i32 = mem::transmute(&*x); // launder lifetimes
+        let y2 = x as *mut _;
+        let _val = *y1;
+        *y2 += 1;
+    }
+}
+
+fn disjoint_mutable_subborrows() {
+    struct Foo {
+        a: String,
+        b: Vec<u32>,
+    }
+
+    unsafe fn borrow_field_a<'a>(this: *mut Foo) -> &'a mut String {
+        &mut (*this).a
+    }
+
+    unsafe fn borrow_field_b<'a>(this: *mut Foo) -> &'a mut Vec<u32> {
+        &mut (*this).b
+    }
+
+    let mut foo = Foo { a: "hello".into(), b: vec![0, 1, 2] };
+
+    let ptr = &mut foo as *mut Foo;
+
+    let a = unsafe { borrow_field_a(ptr) };
+    let b = unsafe { borrow_field_b(ptr) };
+    b.push(4);
+    a.push_str(" world");
+    assert_eq!(format!("{:?} {:?}", a, b), r#""hello world" [0, 1, 2, 4]"#);
+}
+
+fn raw_ref_to_part() {
+    struct Part {
+        _lame: i32,
+    }
+
+    #[repr(C)]
+    struct Whole {
+        part: Part,
+        extra: i32,
+    }
+
+    let it = Box::new(Whole { part: Part { _lame: 0 }, extra: 42 });
+    let whole = ptr::addr_of_mut!(*Box::leak(it));
+    let part = unsafe { ptr::addr_of_mut!((*whole).part) };
+    let typed = unsafe { &mut *(part as *mut Whole) };
+    assert!(typed.extra == 42);
+    drop(unsafe { Box::from_raw(whole) });
+}
+
+/// When casting an array reference to a raw element ptr, that should cover the whole array.
+fn array_casts() {
+    let mut x: [usize; 2] = [0, 0];
+    let p = &mut x as *mut usize;
+    unsafe {
+        *p.add(1) = 1;
+    }
+
+    let x: [usize; 2] = [0, 1];
+    let p = &x as *const usize;
+    assert_eq!(unsafe { *p.add(1) }, 1);
+}
+
+/// Transmuting &&i32 to &&mut i32 is fine.
+fn mut_below_shr() {
+    let x = 0;
+    let y = &x;
+    let p = unsafe { core::mem::transmute::<&&i32, &&mut i32>(&y) };
+    let r = &**p;
+    let _val = *r;
+}
+
+fn wide_raw_ptr_in_tuple() {
+    let mut x: Box<dyn std::any::Any> = Box::new("ouch");
+    let r = &mut *x as *mut dyn std::any::Any;
+    // This triggers the visitor-based recursive retagging. It is *not* supposed to retag raw
+    // pointers, but then the visitor might recurse into the "fields" of a wide raw pointer and
+    // finds a reference (to a vtable) there that it wants to retag... and that would be Wrong.
+    let pair = (r, &0);
+    let r = unsafe { &mut *pair.0 };
+    // Make sure the fn ptr part of the vtable is still fine.
+    r.type_id();
+}
+
+fn not_unpin_not_protected() {
+    // `&mut !Unpin`, at least for now, does not get `noalias` nor `dereferenceable`, so we also
+    // don't add protectors. (We could, but until we have a better idea for where we want to go with
+    // the self-referential-generator situation, it does not seem worth the potential trouble.)
+    use std::marker::PhantomPinned;
+
+    pub struct NotUnpin(i32, PhantomPinned);
+
+    fn inner(x: &mut NotUnpin, f: fn(&mut NotUnpin)) {
+        // `f` may mutate, but it may not deallocate!
+        f(x)
+    }
+
+    inner(Box::leak(Box::new(NotUnpin(0, PhantomPinned))), |x| {
+        let raw = x as *mut _;
+        drop(unsafe { Box::from_raw(raw) });
+    });
+}