diff --git a/Cargo.lock b/Cargo.lock
index f9ad78e3795..a30ab648c3f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2543,9 +2543,6 @@ dependencies = [
 [[package]]
 name = "miropt-test-tools"
 version = "0.1.0"
-dependencies = [
- "regex",
-]
 
 [[package]]
 name = "native-tls"
diff --git a/src/tools/miropt-test-tools/Cargo.toml b/src/tools/miropt-test-tools/Cargo.toml
index 8589a44cf1b..09b4c7d16dc 100644
--- a/src/tools/miropt-test-tools/Cargo.toml
+++ b/src/tools/miropt-test-tools/Cargo.toml
@@ -4,4 +4,3 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-regex = "1.0"
diff --git a/src/tools/miropt-test-tools/src/lib.rs b/src/tools/miropt-test-tools/src/lib.rs
index 7d60033c3e8..4317f23a822 100644
--- a/src/tools/miropt-test-tools/src/lib.rs
+++ b/src/tools/miropt-test-tools/src/lib.rs
@@ -100,14 +100,19 @@ pub fn files_for_miropt_test(
             } else {
                 // Allow-list for file extensions that can be produced by MIR dumps.
                 // Other extensions can be added here, as needed by new dump flags.
-                let ext_re = regex::Regex::new(r#"(\.(mir|dot))$"#).unwrap();
-                let cap = ext_re.captures_iter(test_name).next().unwrap_or_else(|| {
-                    panic!("in {testfile:?}:\nEMIT_MIR has an unrecognized extension: {test_name}")
-                });
-                let extension = cap.get(1).unwrap().as_str();
+                static ALLOWED_EXT: &[&str] = &["mir", "dot"];
+                let Some((test_name_wo_ext, test_name_ext)) = test_name.rsplit_once('.') else {
+                    panic!(
+                        "in {testfile:?}:\nEMIT_MIR has an unrecognized extension: {test_name}, expected one of {ALLOWED_EXT:?}"
+                    )
+                };
+                if !ALLOWED_EXT.contains(&test_name_ext) {
+                    panic!(
+                        "in {testfile:?}:\nEMIT_MIR has an unrecognized extension: {test_name}, expected one of {ALLOWED_EXT:?}"
+                    )
+                }
 
-                expected_file =
-                    format!("{}{}{}", test_name.trim_end_matches(extension), suffix, extension,);
+                expected_file = format!("{}{}.{}", test_name_wo_ext, suffix, test_name_ext);
                 from_file = test_name.to_string();
                 assert!(test_names.next().is_none(), "two mir pass names specified for MIR dump");
                 to_file = None;
diff --git a/src/tools/tidy/src/style.rs b/src/tools/tidy/src/style.rs
index a8aae6f5bc9..28d70b4454c 100644
--- a/src/tools/tidy/src/style.rs
+++ b/src/tools/tidy/src/style.rs
@@ -130,16 +130,20 @@ fn should_ignore(line: &str) -> bool {
     // Matches test annotations like `//~ ERROR text`.
     // This mirrors the regex in src/tools/compiletest/src/runtest.rs, please
     // update both if either are changed.
-    let re = Regex::new("\\s*//(\\[.*\\])?~.*").unwrap();
+    lazy_static::lazy_static! {
+        static ref ANNOTATION_RE: Regex = Regex::new("\\s*//(\\[.*\\])?~.*").unwrap();
+    }
     // For `ui_test`-style UI test directives, also ignore
     // - `//@[rev] compile-flags`
     // - `//@[rev] normalize-stderr-test`
-    let ui_test_long_directives =
+    lazy_static::lazy_static! {
+        static ref UI_TEST_LONG_DIRECTIVES_RE: Regex =
         Regex::new("\\s*//@(\\[.*\\]) (compile-flags|normalize-stderr-test|error-pattern).*")
             .unwrap();
-    re.is_match(line)
+    }
+    ANNOTATION_RE.is_match(line)
         || ANNOTATIONS_TO_IGNORE.iter().any(|a| line.contains(a))
-        || ui_test_long_directives.is_match(line)
+        || UI_TEST_LONG_DIRECTIVES_RE.is_match(line)
 }
 
 /// Returns `true` if `line` is allowed to be longer than the normal limit.