On Wed, Nov 13, 2013 at 4:29 PM, Hendrik Greving <hendrik.greving.in...@gmail.com> wrote: > In case it is determined that a frame pointer is needed (in reload?), > who is supposed to make sure that the register that will hold the > frame pointer is not allocated for general use? We have a customized > register allocation mechanism, but I am trying to figure out / > understand the regular/general case first. For instance I am not sure > if I understand the usage of the fixed_regs table w.r.t. to the frame > pointer. Could anybody shed some light on this by any chance?
On some platforms the frame pointer is in fixed_regs. Those platforms are easy. On most platforms the frame pointer is not in fixed_regs. Those platforms will still define FRAME_POINTER_REGNUM or HARD_FRAME_POINTER_REGNUM. The register allocator will set the function-specific variable frame_pointer_needed to indicate whether the function requires a frame pointer. This test includes a call to the target hook frame_pointer_required. If frame_pointer_needed is true, then FRAME_POINTER_REGNUM or HARD_FRAME_POINTER_REGNUM, as appropriate, will be added to the list of registers that should not be allocated. If you have a custom register allocator, you need to do the same. Ian
