add tracking UI test for upstream LLVM issue

Author: Ezrashaw

src/tools/tidy/src/ui_tests.rs

@@ -10,7 +10,7 @@ use std::path::{Path, PathBuf};
 const ENTRY_LIMIT: usize = 900;
 // FIXME: The following limits should be reduced eventually.
 const ISSUES_ENTRY_LIMIT: usize = 1953;
-const ROOT_ENTRY_LIMIT: usize = 894;
+const ROOT_ENTRY_LIMIT: usize = 895;
 
 fn check_entries(tests_path: &Path, bad: &mut bool) {
     let mut directories: HashMap<PathBuf, usize> = HashMap::new();

tests/ui/upstream-llvm/issue-110743-debug-output.rs

@@ -0,0 +1,20 @@
+// this test tracks superfluous debug output from LLVM which we can't control
+
+// build-pass
+// min-llvm-version: 16
+// known-bug: #110743
+
+const SZ: usize = 64_000_000;
+type BigDrop = [String; SZ];
+
+fn f(from_fn: BigDrop) {}
+
+fn f2(_moveme: BigDrop) -> String {
+    let [a, ..] = _moveme;
+    a
+}
+
+fn main() {
+    f(std::array::from_fn(|_| String::new()));
+    f2(std::array::from_fn(|_| String::new()));
+}

tests/ui/upstream-llvm/issue-110743-debug-output.stderr

@@ -0,0 +1,2 @@
+80/7680000120 (0.00%) spills, 7680000040/7680000120 (100.00%) variables
+80/7680000120 (0.00%) spills, 7680000040/7680000120 (100.00%) variables