Zend: add_function_array() fast paths for an empty operand.

Zend/tests/array_addition_empty_operand.phpt

@@ -0,0 +1,125 @@
+--TEST--
+Array addition with an empty operand
+--FILE--
+<?php
+
+function show(string $label, array $result): void
+{
+    $current = key($result);
+    $result[-5] = 'negative';
+    $result[] = 'appended';
+    echo $label, ': current=', json_encode($current), ' keys=', json_encode(array_keys($result)), PHP_EOL;
+}
+
+$empty = [];
+
+echo '-- empty right operand', PHP_EOL;
+$hash = ['x' => 1, 'y' => 2];
+show('hash', $hash + $empty);
+next($hash);
+show('hash, moved pointer', $hash + $empty);
+next($hash);
+show('hash, exhausted pointer', $hash + $empty);
+$list = [1, 2, 3];
+unset($list[2]);
+show('list, stale next index', $list + $empty);
+$emptied = [1];
+unset($emptied[0]);
+show('emptied list', $emptied + $empty);
+
+echo '-- empty left operand', PHP_EOL;
+$hash = ['x' => 1, 'y' => 2];
+show('hash', $empty + $hash);
+next($hash);
+show('hash, moved pointer', $empty + $hash);
+$hash = ['x' => 1, 5 => 2];
+show('hash, integer key', $empty + $hash);
+unset($hash[5]);
+show('hash, removed integer key', $empty + $hash);
+$list = [1, 2, 3];
+show('list', $empty + $list);
+next($list);
+show('list, moved pointer', $empty + $list);
+unset($list[2]);
+show('list, stale next index', $empty + $list);
+$list = [1, 2, 3];
+unset($list[0]);
+show('list, leading hole', $empty + $list);
+show('emptied list on the left', $emptied + ['x' => 1]);
+
+echo '-- both empty', PHP_EOL;
+$popped = [1];
+array_pop($popped);
+show('empty + popped', $empty + $popped);
+show('popped + empty', $popped + $empty);
+show('empty + emptied', $empty + $emptied);
+show('emptied + empty', $emptied + $empty);
+
+echo '-- compound assignment', PHP_EOL;
+$target = [];
+$target += $popped;
+show('empty += popped', $target);
+$target = [];
+$target += ['x' => 1, 'y' => 2];
+show('empty += hash', $target);
+$target = ['x' => 1];
+$target += $empty;
+show('hash += empty', $target);
+
+echo '-- the operands are left untouched', PHP_EOL;
+const DEFAULTS = ['a' => 1, 'b' => 2];
+$result = $empty + DEFAULTS;
+$result['c'] = 3;
+$other = DEFAULTS + $empty;
+$other['c'] = 3;
+$target = [];
+$target += DEFAULTS;
+$target['c'] = 3;
+echo json_encode(DEFAULTS), ' ', json_encode($result), ' ', json_encode($other), ' ', json_encode($target), PHP_EOL;
+
+$source = ['k' => 'v'];
+$source['l'] = 'w';
+$copy = $source;
+$source += $empty;
+$source['m'] = 'x';
+$result = $empty + $copy;
+$result['k'] = 'changed';
+echo json_encode($copy), ' ', json_encode($source), ' ', json_encode($result), PHP_EOL;
+
+$value = 1;
+$withReference = ['r' => &$value];
+$result = $empty + $withReference;
+$result['r'] = 2;
+echo $value, PHP_EOL;
+
+?>
+--EXPECT--
+-- empty right operand
+hash: current="x" keys=["x","y",-5,-4]
+hash, moved pointer: current="y" keys=["x","y",-5,-4]
+hash, exhausted pointer: current="x" keys=["x","y",-5,-4]
+list, stale next index: current=0 keys=[0,1,-5,3]
+emptied list: current=null keys=[-5,1]
+-- empty left operand
+hash: current="x" keys=["x","y",-5,-4]
+hash, moved pointer: current="x" keys=["x","y",-5,-4]
+hash, integer key: current="x" keys=["x",5,-5,6]
+hash, removed integer key: current="x" keys=["x",-5,-4]
+list: current=0 keys=[0,1,2,-5,3]
+list, moved pointer: current=0 keys=[0,1,2,-5,3]
+list, stale next index: current=0 keys=[0,1,-5,2]
+list, leading hole: current=1 keys=[1,2,-5,3]
+emptied list on the left: current="x" keys=["x",-5,1]
+-- both empty
+empty + popped: current=null keys=[-5,-4]
+popped + empty: current=null keys=[-5,0]
+empty + emptied: current=null keys=[-5,-4]
+emptied + empty: current=null keys=[-5,1]
+-- compound assignment
+empty += popped: current=null keys=[-5,-4]
+empty += hash: current="x" keys=["x","y",-5,-4]
+hash += empty: current="x" keys=["x",-5,-4]
+-- the operands are left untouched
+{"a":1,"b":2} {"a":1,"b":2,"c":3} {"a":1,"b":2,"c":3} {"a":1,"b":2,"c":3}
+{"k":"v","l":"w"} {"k":"v","l":"w","m":"x"} {"k":"changed","l":"w"}
+2

Zend/zend_operators.c

@@ -1198,6 +1198,34 @@ static zend_never_inline void ZEND_FASTCALL add_function_array(zval *result, con
 		/* $a += $a */
 		return;
 	}
+	if (zend_hash_num_elements(Z_ARRVAL_P(op2)) == 0 &&
+		Z_ARRVAL_P(op1)->nInternalPointer < Z_ARRVAL_P(op1)->nNumUsed) {
+		/* $a += [] or $a + [], unless the internal pointer is past the
+		 * end as zend_array_dup() would reset it */
+		if (result != op1) {
+			ZVAL_COPY(result, op1);
+		}
+		return;
+	}
+	if (zend_hash_num_elements(Z_ARRVAL_P(op1)) == 0 &&
+		zend_hash_num_elements(Z_ARRVAL_P(op2)) != 0) {
+		/* [] + $a or $a += $b with an empty $a, $b is shared only if a
+		 * merge would give the same array: op1 never had an integer key,
+		 * $b has its pointer on the first element and its next free
+		 * index is not stale */
+		const HashTable *src = Z_ARRVAL_P(op2);
+		zend_long next_free = HT_IS_PACKED(src) ? (zend_long) src->nNumUsed : ZEND_LONG_MIN;
+		if (Z_ARRVAL_P(op1)->nNextFreeElement == ZEND_LONG_MIN &&
+			src->nInternalPointer == 0 &&
+			src->nNextFreeElement == next_free) {
+			zend_array *old = result == op1 ? Z_ARR_P(result) : NULL;
+			ZVAL_COPY(result, op2);
+			if (old) {
+				zend_array_release(old);
+			}
+			return;
+		}
+	}
 	if (result != op1) {
 		ZVAL_ARR(result, zend_array_dup(Z_ARR_P(op1)));
 	} else {