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This is generalization of idea, that was previously usesd for caching resolution of class_entries in zend_type. Now very similar mechanizm is used for general zend_string into zend_class_entry resolution. Interned zend_string with IS_STR_CLASS_NAME_MAP_PTR GC_FLAG uses its refcount to adress corresponding zend_class_entry cache slot. The refcount keeps an offset to this slot from CG(map_ptr_base). Flag may be checked by ZSTR_HAS_CE_CACHE(str), cache slot may be read by ZSTR_GET_CE_CACHE(str) and set by ZSTR_SET_CE_CACHE(str, ce).
Opcache JIT
This is the implementation of Opcache's JIT (Just-In-Time compiler), This converts the PHP Virtual Machine's opcodes into x64/x86 assembly, on POSIX platforms and Windows.
It generates native code directly from PHP byte-code and information collected by the SSA static analysis framework (a part of the opcache optimizer). Code is usually generated separately for each PHP byte-code instruction. Only a few combinations are considered together (e.g. compare + conditional jump).
See the JIT RFC for more details.
DynAsm
This uses DynAsm (developed for LuaJIT project) for the generation of native code. It's a very lightweight and advanced tool, but does assume good, and very low-level development knowledge of target assembler languages. In the past we tried LLVM, but its code generation speed was almost 100 times slower, making it prohibitively expensive to use.
The unofficial DynASM Documentation has a tutorial, reference, and instruction listing.
zend_jit_x86.dasc gets automatically converted to zend_jit_x86.c by the bundled
dynasm during make.