From 15d8c008203208402bd234aec66b07dbe2824ec7 Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Fri, 13 May 2022 11:25:51 -0700
Subject: Test RefCell aliasing

---
 src/test/codegen/noalias-refcell.rs | 14 ++++++++++++++
 src/test/ui/issues/issue-63787.rs   | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 src/test/codegen/noalias-refcell.rs
 create mode 100644 src/test/ui/issues/issue-63787.rs

(limited to 'src')

diff --git a/src/test/codegen/noalias-refcell.rs b/src/test/codegen/noalias-refcell.rs
new file mode 100644
index 00000000000..dba73937abf
--- /dev/null
+++ b/src/test/codegen/noalias-refcell.rs
@@ -0,0 +1,14 @@
+// compile-flags: -O -C no-prepopulate-passes -Z mutable-noalias=yes
+
+#![crate_type = "lib"]
+
+use std::cell::{Ref, RefCell, RefMut};
+
+// Make sure that none of the arguments get a `noalias` attribute, because
+// the `RefCell` might alias writes after either `Ref`/`RefMut` is dropped.
+
+// CHECK-LABEL: @maybe_aliased(
+// CHECK-NOT: noalias
+// CHECK-SAME: %_refcell
+#[no_mangle]
+pub unsafe fn maybe_aliased(_: Ref<'_, i32>, _: RefMut<'_, i32>, _refcell: &RefCell<i32>) {}
diff --git a/src/test/ui/issues/issue-63787.rs b/src/test/ui/issues/issue-63787.rs
new file mode 100644
index 00000000000..cba079b2315
--- /dev/null
+++ b/src/test/ui/issues/issue-63787.rs
@@ -0,0 +1,36 @@
+// run-pass
+// compile-flags: -O
+
+// Make sure that `Ref` and `RefMut` do not make false promises about aliasing,
+// because once they drop, their reference/pointer can alias other writes.
+
+// Adapted from comex's proof of concept:
+// https://github.com/rust-lang/rust/issues/63787#issuecomment-523588164
+
+use std::cell::RefCell;
+use std::ops::Deref;
+
+pub fn break_if_r_is_noalias(rc: &RefCell<i32>, r: impl Deref<Target = i32>) -> i32 {
+    let ptr1 = &*r as *const i32;
+    let a = *r;
+    drop(r);
+    *rc.borrow_mut() = 2;
+    let r2 = rc.borrow();
+    let ptr2 = &*r2 as *const i32;
+    if ptr2 != ptr1 {
+        panic!();
+    }
+    // If LLVM knows the pointers are the same, and if `r` was `noalias`,
+    // then it may replace this with `a + a`, ignoring the earlier write.
+    a + *r2
+}
+
+fn main() {
+    let mut rc = RefCell::new(1);
+    let res = break_if_r_is_noalias(&rc, rc.borrow());
+    assert_eq!(res, 3);
+
+    *rc.get_mut() = 1;
+    let res = break_if_r_is_noalias(&rc, rc.borrow_mut());
+    assert_eq!(res, 3);
+}
-- 
cgit 1.4.1-3-g733a5


From 1c3921fa43ecc6438a1f4d5365d2f99caad7b847 Mon Sep 17 00:00:00 2001
From: Josh Stone <jistone@redhat.com>
Date: Mon, 16 May 2022 17:39:34 -0700
Subject: Read the Ref/RefMut pointer in natvis

---
 src/etc/natvis/libcore.natvis | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

(limited to 'src')

diff --git a/src/etc/natvis/libcore.natvis b/src/etc/natvis/libcore.natvis
index 643590fc977..a4e8a57e4b1 100644
--- a/src/etc/natvis/libcore.natvis
+++ b/src/etc/natvis/libcore.natvis
@@ -7,15 +7,15 @@
     </Expand>
   </Type>
   <Type Name="core::cell::Ref&lt;*&gt;">
-    <DisplayString>{value}</DisplayString>
+    <DisplayString>{value.pointer}</DisplayString>
     <Expand>
-      <ExpandedItem>value</ExpandedItem>
+      <ExpandedItem>value.pointer</ExpandedItem>
     </Expand>
   </Type>
   <Type Name="core::cell::RefMut&lt;*&gt;">
-    <DisplayString>{value}</DisplayString>
+    <DisplayString>{value.pointer}</DisplayString>
     <Expand>
-      <ExpandedItem>value</ExpandedItem>
+      <ExpandedItem>value.pointer</ExpandedItem>
     </Expand>
   </Type>
   <Type Name="core::cell::RefCell&lt;*&gt;">
-- 
cgit 1.4.1-3-g733a5