These `-m' options are defined for the IBM RT PC:

-min-line-mul: Use an in-line code sequence for integer multiplies. This is the default.
-mcall-lib-mul: Call lmul$$ for integer multiples.
-mfull-fp-blocks: Generate full-size floating point data blocks, including the minimum amount of scratch space recommended by IBM. This is the default.
-mminimum-fp-blocks: Do not include extra scratch space in floating point data blocks. This results in smaller code, but slower execution, since scratch space must be allocated dynamically.
-mfp-arg-in-fpregs: Use a calling sequence incompatible with the IBM calling convention in which floating point arguments are passed in floating point registers. Note that varargs.h and stdargs.h will not work with floating point operands if this option is specified.
-mfp-arg-in-gregs: Use the normal calling convention for floating point arguments. This is the default.
-mhc-struct-return: Return structures of more than one word in memory, rather than in a register. This provides compatibility with the MetaWare HighC (hc) compiler. Use the option `-fpcc-struct-return' for compatibility with the Portable C Compiler (pcc).
-mnohc-struct-return: Return some structures of more than one word in registers, when convenient. This is the default. For compatibility with the IBM-supplied compilers, use the option `-fpcc-struct-return' or the option `-mhc-struct-return'.