> Am 17.02.2015 um 00:30 schrieb Rasmus Lerdorf <ras...@lerdorf.com>: > > On 02/16/2015 03:04 PM, Bob Weinand wrote: >> I'd like to show you my recent work on a jumptable optimization for switches. >> >> https://github.com/php/php-src/pull/1048 >> <https://github.com/php/php-src/pull/1048> >> >> It is a fully transparent optimization of switches, by putting a new >> ZEND_SWITCH opcode at the top of the switch in case we can build a >> jumptable, which is the case if the cases are only scalars (no doubles) or >> evaluate to them at compile-time. >> >> Switches tend to be big sometimes with a lot of static (literals or >> constants usually) cases, which was a comparison for each case, and now just >> a simple hashtable lookup is needed, which greatly improves performance. In >> case where the result of the switch can be determined at compile-time, it >> even replaces the comparisons with a simple ZEND_JMP opcode. >> >> In synthetic benchmarks the results are mind blowing, but in practice, >> benefits mostly are stateful userland parsers (often called with sometimes >> big switches), where it makes it a few percent faster. (For more concrete >> numbers see https://github.com/php/php-src/pull/1048#issuecomment-73032647) >> >> As the optimization is only done if there are 3 or more cases, the lookup is >> always faster than the single comparisons. So there's no negative >> performance impact. >> >> It already works, except with opcache where the CFG optimization pass still >> lacks support. Dmitry or Laruence volunteered to add support for opcache. >> >> I'd like to know if there are any technical objections to the PR. If not, >> they will add opcache support and merge it in. > > It looks ok to me if Xinchen or Dmitry gets the opcache support working > for it and the feature is stabilized in time. I gave it a try and it is > segfaulting for me (no opcache): > > ==5612== Command: sapi/cli/php -n jump.php > ==5612== > ==5612== Invalid read of size 4 > ==5612== at 0xA64637: _zend_is_inconsistent (zend_hash.c:44) > ==5612== by 0xA65749: _zend_hash_add_or_update_i (zend_hash.c:427) > ==5612== by 0xA65AF9: _zend_hash_add (zend_hash.c:489) > ==5612== by 0xA37E28: zend_hash_add_ptr (zend_hash.h:458) > ==5612== by 0xA39B0A: zend_hash_add_constant (zend_constants.c:486) > ==5612== by 0xA39D01: zend_register_constant (zend_constants.c:523) > ==5612== by 0xA389E9: zend_register_long_constant (zend_constants.c:194) > ==5612== by 0xA3855C: zend_register_standard_constants > (zend_constants.c:116) > ==5612== by 0xA52D6E: zend_startup (zend.c:671) > ==5612== by 0x9C7FAA: php_module_startup (main.c:2099) > ==5612== by 0xAFA460: php_cli_startup (php_cli.c:421) > ==5612== by 0xAFC4D6: main (php_cli.c:1335) > ==5612== Address 0x8 is not stack'd, malloc'd or (recently) free'd > > And jump.php is: > > <?php > $a = 1; > switch($a) { > case 0: echo 0; break; > case 1: echo 1; break; > case 2: echo 1; break; > case 3: echo 1; break; > case 4: echo 1; break; > case 5: echo 1; break; > case 6: echo 1; break; > case 7: echo 1; break; > case 8: echo 1; break; > case 9: echo 1; break; > } > > -Rasmus
Hey, this doesn't really look related to my patch. Did you do something wrong when cloning my branch? Or forget a make clean or similar? Locally it works for me and echoes 1 as expected. Bob
