Static Single Assignment Form (SSA)

SSA stands for Static Single Assignment form. It is a property of code where each variable is assigned exactly once, making it easier to analyze and optimize.

SSA is used in the PHP engine, and it helps with several aspects of the execution engine:

  • Performance: SSA enables more efficient code optimization, such as dead code elimination, constant propagation, and loop optimizations.

  • JIT Compilation: the PHP JIT compiler, introduced in PHP 8.0, benefits from SSA to generate faster machine code.

Documentation

See also Building SSA in a Compiler for PHP.

Related : Just In Time (JIT), Performance, Static Code Analysis (SCA), Control Flow Graph