This is a new transparent technology that eliminates overhead of PHP class inheritance.
PHP classes are compiled and cached (by opcahce) separately, however their "linking" was done at run-time - on each request. The process of "linking" may involve a number of compatibility checks and borrowing methods/properties/constants form parent and traits. This takes significant time, but the result is the same on each request.
Inheritance Cache performs "linking" for unique set of all the depending classes (parent, interfaces, traits, property types, method types involved into compatibility checks) once and stores result in opcache shared memory. As a part of the this patch, I removed limitations for immutable classes (unresolved constants, typed properties and covariant type checks). So now all classes stored in opcache are "immutable". They may be lazily loaded into process memory, if necessary, but this usually occurs just once (on first linking).
The patch shows 8% improvement on Symphony "Hello World" app.
Due to ASLR restrictions, preloading on Windows does not work with
any code that has preloading dependencies on internal classes.
This effectively makes it unusable for any non-trivial codebase.
Instead of pretending like preloading is going to work, only to
make people realize that it really doesn't once they get beyond
a dummy example, we disable support for preloading on Windows
entirely.
Closes GH-4999.
Max Semenik