[Skylark] Optimize UserDefinedFunction.

Java's iterator overhead is significant (2X slower than using indices), so
it's worthwhile to use indices for hot code.

Closes #5737.

PiperOrigin-RevId: 207088309

1 files changed, 3 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java b/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
index a892bda51b..8410dd7653 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/UserDefinedFunction.java
@@ -71,9 +71,9 @@ public class UserDefinedFunction extends BaseFunction {
       env.enterScope(this, lexicalFrame, ast, definitionGlobals);
 
       // Registering the functions's arguments as variables in the local Environment
-      int i = 0;
-      for (String name : names) {
-        env.update(name, arguments[i++]);
+      // foreach loop is not used to avoid iterator overhead
+      for (int i = 0; i < names.size(); ++i) {
+        env.update(names.get(i), arguments[i]);
       }
 
       Eval eval = Eval.fromEnvironment(env);