Add regression test for issue 144329

tests/codegen-llvm/issues/issue-144329-niched-option-check.rs

@@ -0,0 +1,64 @@
+//! Ensure that redundant null checks on `&mut T` from `Option<(_, &mut T)>` are eliminated.
+
+//@ compile-flags: -Copt-level=3
+
+#![crate_type = "lib"]
+
+type T = [u64; 4];
+
+// CHECK-LABEL: @f0(
+#[no_mangle]
+pub fn f0(stack: &mut Stack, f: fn(&T)) -> bool {
+    // CHECK-NOT: icmp eq ptr.*null.*
+    f_impl::<0>(stack, f)
+}
+
+// CHECK-LABEL: @f1(
+#[no_mangle]
+pub fn f1(stack: &mut Stack, f: fn(&T)) -> bool {
+    // CHECK-NOT: icmp eq ptr.*null.*
+    f_impl::<1>(stack, f)
+}
+
+// CHECK-LABEL: @f2(
+#[no_mangle]
+pub fn f2(stack: &mut Stack, f: fn(&T)) -> bool {
+    // CHECK-NOT: icmp eq ptr.*null.*
+    f_impl::<2>(stack, f)
+}
+
+#[inline(always)]
+fn f_impl<const N: usize>(stack: &mut Stack, f: fn(&T)) -> bool {
+    let Some((a, b)) = stack.popn_top::<N>() else {
+        return false;
+    };
+    a.iter().for_each(f);
+    f(b);
+    true
+}
+
+pub struct Stack {
+    data: Vec<T>,
+}
+
+impl Stack {
+    #[inline]
+    fn popn_top<const N: usize>(&mut self) -> Option<([T; N], &mut T)> {
+        if self.data.len() < N + 1 {
+            return None;
+        }
+        unsafe { Some((self.popn_unchecked(), self.top_unchecked())) }
+    }
+
+    unsafe fn popn_unchecked<const N: usize>(&mut self) -> [T; N] {
+        core::array::from_fn(|_| unsafe { self.pop_unchecked() })
+    }
+
+    unsafe fn pop_unchecked(&mut self) -> T {
+        self.data.pop().unwrap_unchecked()
+    }
+
+    unsafe fn top_unchecked(&mut self) -> &mut T {
+        self.data.last_mut().unwrap_unchecked()
+    }
+}