Format timer labels only when recording is enabled

src/driver.rs

@@ -823,11 +823,12 @@ fn run_tasks<E: Arch>(
 
     work.into_par_iter().for_each(|(task, mut bufs)| {
         let name = ctx.chunk_header(task.chunk).name;
-        let _t = timer.child(&if name.is_empty() {
-            "(header)".to_string()
+        let name = if name.is_empty() {
+            bstr::BStr::new("(header)")
         } else {
-            name.to_string()
-        });
+            name
+        };
+        let _t = timer.child(name);
         let mut bufs = bufs.drain(..);
         let own = bufs.next().unwrap();
         match task.chunk {

src/util/perf.rs

@@ -183,7 +183,7 @@ impl Timers {
         self.start_child(name, parent)
     }
 
-    fn start_child(&self, name: &str, parent: Option<usize>) -> Timer {
+    fn start_child(&self, name: impl std::fmt::Display, parent: Option<usize>) -> Timer {
         let Some(records) = &self.records else {
             return self.inactive();
         };
@@ -265,7 +265,7 @@ impl Timer {
     /// Starts a timer nested in this one. Timers started from parallel
     /// tasks name their parent this way, since which timer started last
     /// says nothing about nesting then.
-    pub fn child(&self, name: &str) -> Timer {
+    pub fn child(&self, name: impl std::fmt::Display) -> Timer {
         self.timers.start_child(name, Some(self.index))
     }
 
@@ -285,7 +285,7 @@ impl Timer {
 }
 
 impl TimerHandle {
-    pub fn child(&self, name: &str) -> Timer {
+    pub fn child(&self, name: impl std::fmt::Display) -> Timer {
         self.timers.start_child(name, Some(self.parent))
     }
 }