Re: Does PHP ever stack allocate?

Hi Olle, > Thanks Sara! I realize I should have been more precise: Can PHP > allocate non-reference counted memory that automatically is freed when > leaving scope, similar to what Go does with escape analysis? > > Article describing the Go mechanism: > > https://segment.com/blog/allocation-efficiency-in-high-performance-go-services/ Could you give some concrete examples of what type of code you're talking about? As Sara Golemon said, scalars (null, bool, int, float) are allocated on a php call frame, and the call frames go on a stack. That stack is separate from the C stack, but still a stack The call frame is "freed" when leaving scope - i.e. that part of the stack will be reused on subsequent calls. > A single PHP call frame holds a block of storage space for (among other > things) all* local variables. This can be thought of analogously to "the > stack" as it's used by native applications. Basic scalars (null, bool, > int, float) sit in this space with no additional pointers to anywhere. > Non-scalars use pointers to elsewhere in the heap to store the actual > payload. This isn't unique to PHP, as these structures have runtime > determined size and thus can't** be stack allocated. https://nikic.github.io/2017/04/14/PHP-7-Virtual-machine.html may help if you want to learn more about what the PHP VM currently does > So what’s the difference between TMP and VAR? Not much. > The distinction was inherited from PHP 5, where TMPs were VM stack allocated, > while VARs were heap allocated. In PHP 7 all variables are stack allocated. > As such, nowadays the main difference between TMPs and VARs is that only the latter are allowed > to contain REFERENCEs > (this allows us to elide DEREFs on TMPs). Furthermore VARs may hold two types of special > values, > namely class entries and INDIRECT values. The latter are used to handle non-trivial > assignments. -Tyson