simpler_variable_search.diff

diff --git a/core/src/main/java/org/jruby/parser/StaticScope.java b/core/src/main/java/org/jruby/parser/StaticScope.java
index 66c9b71c61..32c644f730 100644
--- a/core/src/main/java/org/jruby/parser/StaticScope.java
+++ b/core/src/main/java/org/jruby/parser/StaticScope.java
@@ -37,6 +37,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.Map;
 import java.util.function.BiConsumer;
 import java.util.function.IntFunction;
 
@@ -93,6 +94,10 @@ public class StaticScope implements Serializable {
     // as key to Symbol table for actual encoded versions].
     private String[] variableNames;
 
+    // A set containing all known variable names, to quickly check for existing definitions.
+    // This is only used at parse/construction time.
+    private Map<String, Integer> knownVariables;
+
     private int variableNamesLength;
 
     // Arity of this scope if there is one
@@ -365,10 +370,11 @@ public class StaticScope implements Serializable {
     }
 
     private int findVariableName(String name) {
-        for (int i = 0; i < variableNames.length; i++) {
-            if (name.equals(variableNames[i])) return i;
+        Integer index;
+        if (knownVariables == null || (index = knownVariables.get(name)) == null) {
+            return -1;
         }
-        return -1;
+        return index;
     }
 
     /**
@@ -635,7 +641,10 @@ public class StaticScope implements Serializable {
         System.arraycopy(variableNames, 0, newVariableNames, 0, variableNames.length);
         variableNames = newVariableNames;
         variableNamesLength = newVariableNames.length;
-        variableNames[variableNames.length - 1] = name;
+        int newIndex = variableNames.length - 1;
+        variableNames[newIndex] = name;
+        if (knownVariables == null) knownVariables = new HashMap<>();
+        knownVariables.put(name, newIndex);
     }
 
     /**