These all effect various optimizations done by the compiler. These cannot be used to turn on and off optimizations for specific parts of the code -- the last one parsed will be the one in effect.
For a complete description of each, including warnings and caveats, please refer to the Optimizations chapter of the Jalv2 Compiler Options document
Format:
PRAGMA OPT EXPR_REDUCE { YES | NO | }
| * YES --expression reduction is performed |
| NO -- expression reduction is not performed |