Rollup merge of #93649 - WaffleLapkin:regression_test_80309, r=oli-obk

Add regression tests for issue 80309

Closes #80309 😝

I'm not sure where to put the tests, is `ui/issues` the right place for this kind of tests?

src/test/ui/ptr_ops/issue-80309-safe.rs

@@ -0,0 +1,17 @@
+// run-pass
+// min-llvm-version: 13.0
+// compiler-flags: -O
+
+// Regression test for issue #80309
+
+pub fn zero(x: usize) -> usize {
+    std::ptr::null::<i8>().wrapping_add(x) as usize - x
+}
+pub fn qux(x: &[i8]) -> i8 {
+    x[zero(x.as_ptr() as usize)]
+}
+
+fn main() {
+    let z = vec![42, 43];
+    println!("{}", qux(&z));
+}

src/test/ui/ptr_ops/issue-80309.rs

@@ -0,0 +1,14 @@
+// run-pass
+// min-llvm-version: 13.0
+// compiler-flags: -O
+
+// Regression test for issue #80309
+
+pub unsafe fn foo(x: *const i8) -> i8 {
+    *x.wrapping_sub(x as _).wrapping_add(x as _)
+}
+
+fn main() {
+    let x = 42;
+    println!("{}", unsafe { foo(&x) });
+}