The P4C compiler is a compiler infrastructure for the P4 compiler designed with the following goals:

Support current and future versions of P4
Support multiple back-ends
- Generate code for ASICs, NICs, FPGAs, software switches and other targets
Provide support for other tools (debuggers, IDEs, control-plane, etc.)
Open-source front-end
Extensible architecture (easy to add new passes and optimizations)
Use modern compiler techniques (immutable IR, visitor patterns, strong type checking, etc.)
Comprehensive testing

Additional documentation

The documentation for P4_16 and P4Runtime is available here
the core design of the compiler intermediate representation (IR) and the visitor patterns are briefly described in IR
The migration guide describes how P4_14 (v1.0) programs are translated into P4_16 programs