On Mon, Mar 23, 2015 at 11:41 PM, Dmitry Stogov <dmi...@zend.com> wrote:
> Hi, > > Recently, Xinchen and me worked on optimization that eliminates useless > reallocations and copying during string concatenation (ZEND_ADD_STRING and > family + ZEND_CONCAT). > > The idea comes from ropes, but adopted especially for our needs. > Rope is popular data structure in languages with immutable strings. > http://en.wikipedia.org/wiki/Rope_%28data_structure%29 > > We don't try to use ropes everywhere in the engine (at least it's too > later for 7.0), only for concatenation. > > The first branch uses ropes only instead of ZEND_ADD_STRING and family. > This must be safe. The only problem is possible memory leaks on exception > (but we already have this problem anyway). The simplest way to understand > the patch - read code for new opcodes in zend_vm_def.h. > > https://github.com/php/php-src/pull/1194/files > > The second branch in addition uses ropes for series of ZEND_CONCAT. It > disables calls to do_operation(ZEND_CONCAT) handler of custom internal > classes. > > https://github.com/php/php-src/pull/1195/files > > Both make slight speed improvement (first +0.3%, second +0.6% on wordpress > home page). > > We don't currently use ability to override CONCAT behavior in internal > classes, and I'm not sure if it may be useful at all. (For example Lua > doesn't provide concat meta-method). May be remove it? > Overloading concat operator will be useful in the future for the implementation of the UString class, for example. Nikita
