On Fri, May 28, 2021 at 9:00 PM Mark Randall <marand...@php.net> wrote:
> On 28/05/2021 15:31, Nikita Popov wrote: > > This is a more complex case. In this case the compiler doesn't know in > > advance whether the argument is passed by value or by reference. What > > happens here is: > > > I'm trying to wrap my head around this, but if a function arg can handle > this, does something internal to the engine preclude fetching in write > context, after already fetching in read context, other than performance? > > So can the initial fetch be performed with FETCH_DIM_R, handling the > object case + any other scalars, and if and only if the value is an > array and operating on what would traditionally be a by-ref, repeating > the previous lookup with FETCH_DIM_W? > This is theoretically possible, in that this is exactly how $a[$b][$c] ??= $d is implemented. Everything is first fetched as FETCH_DIM_IS and then again as FETCH_DIM_W if an assignment is necessary. However, this does require emitting both fetch sequences, with one guarded by a branch, together with temporary copies to allow re-fetching without re-evaluating side-effecting operands. Of course, it also has fun interactions with magic ArrayAccess/__get, in which case both fetches may produce different results. All this is something we can live with for the ??= operator, but not for every single method call. Regards, Nikita
