Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size.

Generate floating-point comparison instructions that compare with respect to the rE epsilon register.

Generate code that passes function parameters and return values that (in the called function) are seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and up.

When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones.

Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used.

Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the PREFIX assembly directive.

Generate an executable in the ELF format, rather than the default mmo format used by the mmix simulator.

Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch.

Generate (do not generate) code that uses base addresses. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno-base-addresses.