ideas to improve compiler support for romable code

[irmen]

To be able to build programs that can be put into ROM (for rom programs or stuff like a NES cartridge game, for instance), a couple of things are required.
Most notably:

• no "inline" variables (only zeropage and bss)
• no self-modifying code

Currently both are not achieved by the compiler.

An idea around better situation concerning self-modifying code is:

• add a compiler flag to report self-modifying code issues
• make sure that the compiler doesn't generate any self-modifying code in the codegen
• or, alternatively, print a warning/error when it (still) does
• introduce a tag for asmsub's that marks them as using self-modifying code. This requires a review of ALL of the library asmsub routines and mark them correctly.
• this does leave all other included or inlined asm to do whatever it likes undetected.....

[tallLeRoy]

the tag should make it out the the listing file, so after compile the coder can search for the tag in the listing to find the areas not ready for ROM

[irmen]

Probably should ignore the issues with the library code at first and concentrate on looking what needs to be done to get the code-generator in shape for this.