On 04/05/2016 12:04 PM, Derick Rethans wrote:
On Tue, 5 Apr 2016, Dmitry Stogov wrote:
I propose a micro optimization for RETURN statement.
Currently "return $x" increments reference counter of $x, then in
zend_leave_helper() we perform zval_ptr_dtor() on the same $x.
The patch sets the original value of $x to null in first place, so
zval_ptr_dtor() is not going to be called.
https://gist.github.com/dstogov/36f68b206242a39691ac539c2fc85d40
the performance impact is invisible (0.1% less instruction retired on
Wordpress).
It breaks sapi/phpdbg/tests/breakpoints_005.phpt, but this is probably
not a big deal.
BTW: this change may affect debuggers in some other way.
I'd like to know why this breaks before saying something. It'd be a PITA
if this micro optimisation wouldn't actually do a lot performance wise,
but makes some debugging not possible.
Actually, the patch has a bug.
It doesn't take into account that "return $x;" might be used in global
scope.
Setting $x to NULL in this case isn't right, of course.
Introducing another check would probably negate the effect of
micro-optimization.
So, ignore this for now, and sorry for noise.
Thanks. Dmitry.
cheers,
Derick
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