Complete list of optimization flags for the Nios II compiler?

The nios2 compiler is gcc, to get all the parameters use '--help -v'.

I think that, with any level of optimisation, modern gcc will not generate code for C statements that cannot be executed.

Why do you need instructions generated for code that can't be executed?

If you are building a lot of code, you might find it worth while building gcc yourself from the archive on Altera's ftp site. Some of the gcc build options they've used (esp. for gcc4) are sub-optimal in many cases. There are also some patches that give better code for both gcc3 and gcc4.