Optimize Label parsing calls

core/src/main/java/hudson/model/Label.java

@@ -592,10 +592,16 @@ public static Set<LabelAtom> parse(@CheckForNull String labels) {
         final Set<LabelAtom> r = new TreeSet<>();
         labels = fixNull(labels);
         if (labels.length() > 0) {
-            final QuotedStringTokenizer tokenizer = new QuotedStringTokenizer(labels);
-            while (tokenizer.hasMoreTokens())
-                r.add(Jenkins.get().getLabelAtom(tokenizer.nextToken()));
+            Jenkins j = Jenkins.get();
+            LabelAtom labelAtom = j.tryGetLabelAtom(labels);
+            if (labelAtom == null) {
+                final QuotedStringTokenizer tokenizer = new QuotedStringTokenizer(labels);
+                while (tokenizer.hasMoreTokens())
+                    r.add(j.getLabelAtom(tokenizer.nextToken()));
+            } else {
+                r.add(labelAtom);
             }
+        }
         return r;
     }
 

core/src/main/java/jenkins/model/Jenkins.java

@@ -2114,6 +2114,16 @@ public Label getLabel(String expr) {
         }
     }
 
+    /**
+     * Returns the label atom of the given name, only if it already exists.
+     * @return non-null if the label atom already exists.
+     */
+    public @Nullable LabelAtom tryGetLabelAtom(@CheckForNull String name) {
+        if (name == null)  return null;
+        return (LabelAtom) labels.get(name);
+    }
+
+
     /**
      * Gets all the active labels in the current system.
      */

test/src/test/java/hudson/model/labels/LabelBenchmark.java

@@ -0,0 +1,23 @@
+package hudson.model.labels;
+
+import hudson.model.Label;
+import jenkins.benchmark.jmh.JmhBenchmark;
+import jenkins.benchmark.jmh.JmhBenchmarkState;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.infra.Blackhole;
+
+@JmhBenchmark
+public class LabelBenchmark {
+    public static class MyState extends JmhBenchmarkState {
+    }
+
+    @Benchmark
+    public void simpleLabel(MyState state, Blackhole blackhole) {
+        blackhole.consume(Label.parse("some-label"));
+    }
+
+    @Benchmark
+    public void complexLabel(MyState state, Blackhole blackhole) {
+        blackhole.consume(Label.parse("label1 && label2"));
+    }
+}

test/src/test/java/hudson/model/labels/LabelBenchmarkTest.java

@@ -0,0 +1,38 @@
+package hudson.model.labels;
+
+import static org.junit.Assert.assertTrue;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.concurrent.TimeUnit;
+import org.junit.Ignore;
+import org.junit.Test;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.results.format.ResultFormatType;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.ChainedOptionsBuilder;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+public class LabelBenchmarkTest {
+    @Test
+    @Ignore(value="This is a benchmark, not a test")
+    public void runBenchmark() throws Exception {
+        // run the minimum possible number of iterations
+        ChainedOptionsBuilder options = new OptionsBuilder()
+                .mode(Mode.AverageTime)
+                .forks(1)
+                .result("jmh-report.json")
+                .resultFormat(ResultFormatType.JSON)
+                .operationsPerInvocation(1)
+                .threads(1)
+                .warmupForks(0)
+                .warmupIterations(0)
+                .measurementBatchSize(1)
+                .measurementIterations(1)
+                .timeUnit(TimeUnit.NANOSECONDS)
+                .shouldFailOnError(true)
+                .include(LabelBenchmark.class.getName() + ".*");
+        new Runner(options.build()).run();
+        assertTrue(Files.exists(Paths.get("jmh-report.json")));
+    }
+}