Rollup merge of #115591 - djkoloski:issue_115385, r=cuviper

Add regression test for LLVM 17-rc3 miscompile

Closes #115385, see that issue for more details.

tests/codegen/issues/issue-115385-llvm-jump-threading.rs

@@ -0,0 +1,46 @@
+// compile-flags: -O -Ccodegen-units=1
+
+#![crate_type = "lib"]
+
+#[repr(i64)]
+pub enum Boolean {
+    False = 0,
+    True = 1,
+}
+
+impl Clone for Boolean {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl Copy for Boolean {}
+
+extern "C" {
+    fn set_value(foo: *mut i64);
+    fn bar();
+}
+
+pub fn foo(x: bool) {
+    let mut foo = core::mem::MaybeUninit::<i64>::uninit();
+    unsafe {
+        set_value(foo.as_mut_ptr());
+    }
+
+    if x {
+        let l1 = unsafe { *foo.as_mut_ptr().cast::<Boolean>() };
+        if matches!(l1, Boolean::False) {
+            unsafe {
+                *foo.as_mut_ptr() = 0;
+            }
+        }
+    }
+
+    let l2 = unsafe { *foo.as_mut_ptr() };
+    if l2 == 2 {
+        // CHECK: call void @bar
+        unsafe {
+            bar();
+        }
+    }
+}