Optimize each helper and section iteration

Author: theodorejb

src/HelperOptions.php

@@ -159,20 +159,28 @@ public function iterate(array $items): string
         $ret = '';
         $i = 0;
         $outerFrame = $cx->frame;
-        // Fast path: when only root is in the frame, skip array_replace.
-        $simpleFrame = count($outerFrame) === 1;
         // Pre-allocate bpStack once; mutate [0][0] and [0][1] per iteration.
         // PHP COW ensures the inner array's refcount returns to 1 after $cb() returns,
         // so the next iteration's assignment is an in-place mutation, not a copy.
         $bpStack = [[null, null], ...$this->outerBlockParams];
 
+        // Pre-allocate the iteration frame once; only the 4 per-iteration keys mutate each loop.
+        // Reduces per-iteration allocations from 2 (iterData + COW-on-root-assign) to 1 (COW copy
+        // on the first mutation after $cx->frame = $newFrame shares the array). For non-simple
+        // frames, also eliminates the per-iteration array_replace call.
+        $iterKeys = ['key' => null, 'index' => null, 'first' => null, 'last' => null, '_parent' => $outerFrame];
+        $newFrame = count($outerFrame) === 1
+            ? $iterKeys
+            : array_replace($outerFrame, $iterKeys);
+        // Reference so @root lookups work and root mutations from inside the block are visible
+        // outside it — matches HBS.js shallow-copy semantics for object properties.
+        $newFrame['root'] = &$cx->data['root'];
+
         foreach ($items as $index => $value) {
-            $iterData = ['key' => $index, 'index' => $i, 'first' => $i === 0, 'last' => $i === $last];
-            $newFrame = $simpleFrame ? $iterData : array_replace($outerFrame, $iterData);
-            // Reference so @root lookups work and root mutations from inside the block are visible
-            // outside it — matches HBS.js shallow-copy semantics for object properties.
-            $newFrame['root'] = &$cx->data['root'];
-            $newFrame['_parent'] = $outerFrame;
+            $newFrame['key'] = $index;
+            $newFrame['index'] = $i;
+            $newFrame['first'] = $i === 0;
+            $newFrame['last'] = $i === $last;
             $cx->frame = $newFrame;
 
             $bpStack[0][0] = $value;