The Xtensa instruction set has a code density option that provides
16-bit versions of some of the most commonly used opcodes. Use of these
opcodes can significantly reduce code size. When possible, the
assembler automatically translates instructions from the core
Xtensa instruction set into equivalent instructions from the Xtensa code
density option. This translation can be disabled by using underscore
prefixes (see Opcode Names), by using the
‘--no-transform’ command-line option (see Command
Line Options), or by using the no-transform directive
(see transform).
It is a good idea not to use the density instructions directly. The assembler will automatically select dense instructions where possible. If you later need to use an Xtensa processor without the code density option, the same assembly code will then work without modification.