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.

1 files changed, 16 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;
+}