Insert null checks for pointer dereferences when debug assertions are enabled

Similar to how the alignment is already checked, this adds a check
for null pointer dereferences in debug mode. It is implemented similarly
to the alignment check as a MirPass.

This is related to a 2025H1 project goal for better UB checks in debug
mode: https://github.com/rust-lang/rust-project-goals/pull/177.

10 files changed, 104 insertions, 0 deletions

diff --git a/tests/mir-opt/null_check_references.rs b/tests/mir-opt/null_check_references.rs
new file mode 100644
index 00000000000..85f98865646
--- /dev/null
+++ b/tests/mir-opt/null_check_references.rs
@@ -0,0 +1,16 @@
+//@ compile-flags: -C debug-assertions
+
+struct Null {
+    a: u32,
+}
+
+fn main() {
+    // CHECK-LABEL: fn main(
+    // CHECK-NOT: {{assert.*}}
+    let val: u32 = 42;
+    let val_ref: &u32 = &val;
+    let _access1: &u32 = &*val_ref;
+
+    let val = Null { a: 42 };
+    let _access2: &u32 = &val.a;
+}
diff --git a/tests/ui/abi/segfault-no-out-of-stack.rs b/tests/ui/abi/segfault-no-out-of-stack.rs
index b5af13ebfb5..5e8b4e0dbf2 100644
--- a/tests/ui/abi/segfault-no-out-of-stack.rs
+++ b/tests/ui/abi/segfault-no-out-of-stack.rs
@@ -1,5 +1,6 @@
 //@ run-pass
 //@ needs-subprocess
+//@ compile-flags: -Zub-checks=no -Zmir-enable-passes=-CheckNull
 //@ ignore-fuchsia must translate zircon signal to SIGSEGV/SIGBUS, FIXME (#58590)
 
 #![feature(rustc_private)]
diff --git a/tests/ui/mir/null/addrof_null.rs b/tests/ui/mir/null/addrof_null.rs
new file mode 100644
index 00000000000..0d0b7edeef6
--- /dev/null
+++ b/tests/ui/mir/null/addrof_null.rs
@@ -0,0 +1,14 @@
+// Make sure that we don't insert a check for `addr_of!`.
+//@ run-pass
+//@ compile-flags: -C debug-assertions
+
+struct Field {
+    a: u32,
+}
+
+fn main() {
+    unsafe {
+        let ptr: *const Field = std::ptr::null();
+        let _ptr = core::ptr::addr_of!((*ptr).a);
+    }
+}
diff --git a/tests/ui/mir/null/borrowed_mut_null.rs b/tests/ui/mir/null/borrowed_mut_null.rs
new file mode 100644
index 00000000000..437955c452b
--- /dev/null
+++ b/tests/ui/mir/null/borrowed_mut_null.rs
@@ -0,0 +1,8 @@
+//@ run-fail
+//@ compile-flags: -C debug-assertions
+//@ error-pattern: null pointer dereference occured
+
+fn main() {
+    let ptr: *mut u32 = std::ptr::null_mut();
+    let _ptr: &mut u32 = unsafe { &mut *ptr };
+}
diff --git a/tests/ui/mir/null/borrowed_null.rs b/tests/ui/mir/null/borrowed_null.rs
new file mode 100644
index 00000000000..eb0794efaa5
--- /dev/null
+++ b/tests/ui/mir/null/borrowed_null.rs
@@ -0,0 +1,8 @@
+//@ run-fail
+//@ compile-flags: -C debug-assertions
+//@ error-pattern: null pointer dereference occured
+
+fn main() {
+    let ptr: *const u32 = std::ptr::null();
+    let _ptr: &u32 = unsafe { &*ptr };
+}
diff --git a/tests/ui/mir/null/null_lhs.rs b/tests/ui/mir/null/null_lhs.rs
new file mode 100644
index 00000000000..fd3bc3a78b8
--- /dev/null
+++ b/tests/ui/mir/null/null_lhs.rs
@@ -0,0 +1,10 @@
+//@ run-fail
+//@ compile-flags: -C debug-assertions
+//@ error-pattern: null pointer dereference occured
+
+fn main() {
+    let ptr: *mut u32 = std::ptr::null_mut();
+    unsafe {
+        *(ptr) = 42;
+    }
+}
diff --git a/tests/ui/mir/null/null_rhs.rs b/tests/ui/mir/null/null_rhs.rs
new file mode 100644
index 00000000000..45c8beb3fe8
--- /dev/null
+++ b/tests/ui/mir/null/null_rhs.rs
@@ -0,0 +1,10 @@
+//@ run-fail
+//@ compile-flags: -C debug-assertions
+//@ error-pattern: null pointer dereference occured
+
+fn main() {
+    let ptr: *mut u32 = std::ptr::null_mut();
+    unsafe {
+        let _v = *ptr;
+    }
+}
diff --git a/tests/ui/mir/null/place_without_read.rs b/tests/ui/mir/null/place_without_read.rs
new file mode 100644
index 00000000000..d6bfb089b01
--- /dev/null
+++ b/tests/ui/mir/null/place_without_read.rs
@@ -0,0 +1,10 @@
+// Make sure that we don't insert a check for places that do not read.
+//@ run-pass
+//@ compile-flags: -C debug-assertions
+
+fn main() {
+    let ptr: *const u16 = std::ptr::null();
+    unsafe {
+        let _ = *ptr;
+    }
+}
diff --git a/tests/ui/mir/null/two_pointers.rs b/tests/ui/mir/null/two_pointers.rs
new file mode 100644
index 00000000000..d9f0687fe0d
--- /dev/null
+++ b/tests/ui/mir/null/two_pointers.rs
@@ -0,0 +1,12 @@
+//@ run-fail
+//@ compile-flags: -C debug-assertions
+//@ error-pattern: null pointer dereference occured
+
+fn main() {
+    let ptr = std::ptr::null();
+    let mut dest = 0u32;
+    let dest_ptr = &mut dest as *mut u32;
+    unsafe {
+        *dest_ptr = *(ptr);
+    }
+}
diff --git a/tests/ui/mir/null/zero_sized_access.rs b/tests/ui/mir/null/zero_sized_access.rs
new file mode 100644
index 00000000000..e8aaf820c49
--- /dev/null
+++ b/tests/ui/mir/null/zero_sized_access.rs
@@ -0,0 +1,15 @@
+// Make sure that we don't insert a check for zero-sized reads or writes to
+// null, because they are allowed.
+//@ run-pass
+//@ compile-flags: -C debug-assertions
+
+fn main() {
+    let ptr: *mut () = std::ptr::null_mut();
+    unsafe {
+        *(ptr) = ();
+    }
+    let ptr1: *const () = std::ptr::null_mut();
+    unsafe {
+        let _ptr = *ptr1;
+    }
+}