A deep walkthrough of the REX OpenMP GPU lowerer: directive dispatch, outlining, runtime map arrays, `__tgt_kernel_arguments` construction, generated files, and the tests that keep multi-kernel lowering correct.

An end-to-end walkthrough of REX's OpenMP architecture: why it owns OpenMP parsing, how ompparser feeds Sage AST construction, how lowering generates host and device code, and how the test system keeps the pipeline honest.