Does -fomit-frame-pointer always omit the frame pointer? Is there ever a situation where both the pc and fp need to be setup? Does dynamic stack growth force the fp to be setup? Asking specifically for MIPS32. Thanks!
The frame pointer is not really needed for correct execution, except sometimes for exception unwind. Dynamic stack growth usually requires some kind of a frame pointer, but it is not tied to a particular register, but rather allocated through normal data flow analysis.
Basically, -fomit-frame-pointer demotes the FP from a fixed register assignment to a pseudo register and makes initialisation subject to dead store elimination. So the answer to the first question is no, it doesn't omit it always.