I noticed some time ago, while browsing around ZE sources that as of 5.1, constants are resolved to literals at compile time when possible. What I didn't notice was that this is only done if the constant in question has the CONST_CT_SUBST flag set (which *NO* constants in the stock distribution have set). Tossing this constant onto an assortment of internal constants yields just the result I'd expect; i.e. given a script like:
echo M_PI; The resulting opcodes go from: ZEND_FETCH_CONSTANT ~0 'M_PI' ZEND_ECHO ~0 to: ZEND_ECHO 3.1415926535 All well and good, but it begs the question: Why isn't CT substitution treated as the default for persistent (internal) constants, with an optional NOSUBST flag given as an option? The performance difference between the two wouldn't be large, but every little bit helps. The one problem I see with CT substitution is encoders where the meaning of certain (important) constants would change from system to system, but that sort of exception rule sound more like a job for an INI switch than a general disabling... While y'all kibitz about that, here's another one: Class constant resolution isn't happening during compile time at all currently (with the exception of static initializers). Since class constant resolution requires not one but two hash table lookups, this is actually more useful than normal constant's would be. One of the tricky bits to making this work is the way that class constants are picked up in the parser: fully_qualified_class_name T_PAAMAYIM_NEKUDOTAYIM T_STRING where fully_qualified_class_name reduces from a rule that generates a ZEND_FETCH_CLASS opline. To be able to perform compile-time resolution of class constants, it'd need to be possible to rewind the prior op from within zend_do_fetch_constant() when resolution succeeds (a messy and not-nice approach). The compromise I came up with was to delay the invocation of zend_do_fetch_class() by turning the parser rule into simply: T_STRING T_PAAMAYIM_NEKUDOTAYIM T_STRING Then dispatching from zend_do_fetch_constant() back to zend_do_fetch_class() only when necessary. Here's a diff for review: http://www.libssh2.org/patches/ct_class_constants.diff (I didn't include the .c translation so you'll need bison to build this) -Sara -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
