Support FREE dce with T = QM_ASSIGN src

Author: iluuu1994

Zend/Optimizer/block_pass.c

@@ -289,6 +289,17 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 								MAKE_NOP(opline);
 								++(*opt_count);
 								break;
+							case ZEND_QM_ASSIGN:
+								src->result_type = IS_UNUSED;
+								VAR_SOURCE(opline->op1) = NULL;
+								MAKE_NOP(opline);
+								++(*opt_count);
+								if (src->op1_type & (IS_VAR|IS_TMP_VAR)) {
+									src->opcode = ZEND_FREE;
+								} else {
+									MAKE_NOP(src);
+								}
+								break;
 							default:
 								if (!zend_op_may_elide_result(src->opcode)) {
 									break;