On Fri, Aug 31, 2018 at 3:33 PM, H.J. Lu <hjl.to...@gmail.com> wrote: > On Thu, Aug 30, 2018 at 10:21 AM, Jason Merrill <ja...@redhat.com> wrote: >> >>> r138335 allowed arg_pointer_rtx to be eliminated by either FP or SP, >>> but only when dynamic stack alignment is supported. In this case, >>> arg_pointer_rtx is eliminated by FP even when frame_pointer_needed >>> is false and there is no dynamic stack alignment at all. >>> >>>> gcc_assert (elim == stack_pointer_rtx || (frame_pointer_needed && elim >>>> == hard_frame_pointer_rtx)); >>>> >>>> so as not to allow eliminating to an uninitialized FP. >>> >>> FP isn't uninitialized. It is initialized the same way as in the case of >>> SUPPORTS_STACK_ALIGNMENT is true. >> >> How is that? Why would it be initialized when frame_pointer_needed is >> false? What does it mean for frame_pointer_needed to be false, if >> not, as in the documentation of -fomit-frame-pointer, >> >> "This avoids the instructions to save, set up and restore the frame >> pointer; on many targets it also makes an extra register available." >> >> ? > > A backend may not set up frame pointer even with -fno-omit-frame-pointer. > In the case of x86, hard frame pointer can be represented by stack pointer > - UNITS_PER_WORD. > > This patch adds hard_frame_pointer_from_stack_pointer_plus_offset and > hard_frame_pointer_offset to rtl_data to allow a backend to represent > hard frame pointer as stack pointer + offset.
Shouldn't this be fixed in eliminate_regs rather than dwarf2out? Jason
