On Wed, Aug 29, 2018 at 2:59 PM, H.J. Lu <hjl.to...@gmail.com> wrote: > On Wed, Aug 29, 2018 at 11:33 AM, Jason Merrill <ja...@redhat.com> wrote: >> On Wed, Aug 29, 2018 at 8:47 AM, H.J. Lu <hjl.to...@gmail.com> wrote: >>> On Wed, Aug 8, 2018 at 6:32 AM, H.J. Lu <hjl.to...@gmail.com> wrote: >>>> Assert for SUPPORTS_STACK_ALIGNMENT was added for dynamic stack >>>> alignment. At the time, arg_pointer_rtx would only be eliminated >>>> by either hard_frame_pointer_rtx or stack_pointer_rtx only when >>>> dynamic stack alignment is supported. With >>>> >>>> commit cd557ff63f388ad27c376d0a225e74d3594a6f9d >>>> Author: hjl <hjl@138bc75d-0d04-0410-961f-82ee72b054a4> >>>> Date: Thu Aug 10 15:29:05 2017 +0000 >>>> >>>> i386: Don't use frame pointer without stack access >>>> >>>> When there is no stack access, there is no need to use frame pointer >>>> even if -fno-omit-frame-pointer is used and caller's frame pointer is >>>> unchanged. >>>> >>>> this can happen when there is no dynamic stack alignment. This patch >>>> relaxes SUPPORTS_STACK_ALIGNMENT with !crtl->stack_realign_tried to >>>> allow arg_pointer_rtx to be eliminated by either hard_frame_pointer_rtx >>>> or stack_pointer_rtx when there is no dynamic stack alignment at all. >>>> >>>> gcc/ >>>> >>>> PR debug/86593 >>>> * dwarf2out.c (based_loc_descr): Replace SUPPORTS_STACK_ALIGNMENT >>>> with (SUPPORTS_STACK_ALIGNMENT || !crtl->stack_realign_tried). >>>> (compute_frame_pointer_to_fb_displacement): Likewise. >>>> >>>> gcc/testsuite/ >>>> >>>> PR debug/86593 >>>> * g++.dg/pr86593.C: New test. >>>> >>> >>> PING: >>> >>> https://gcc.gnu.org/ml/gcc-patches/2018-08/msg00559.html >> >> It looks like crtl->stack_realign_tried is only ever set if >> SUPPORTS_STACK_ALIGNMENT, so (SUPPORTS_STACK_ALIGNMENT || >> !crtl->stack_realign_tried) is always true. >> >> If you don't need to use the frame pointer, then frame_pointer_needed >> should be false, so the assert should already allow elimination to the > > frame_pointer_needed is false: > > (gdb) p elim > $1 = (rtx) 0x7fffeadd0390 > (gdb) call debug_rtx (elim) > (reg/f:DI 6 bp) > (gdb) call debug_rtx (reg) > (reg/f:DI 16 argp) > (gdb) p x_rtl.frame_pointer_needed > $2 = false > (gdb) > >> stack pointer. Are we trying to eliminate to the hard frame pointer >> even though we've decided we don't need it? Why? > > In this case, we are trying to eliminate argp to the hard frame pointer.
Right, but why are we trying to do that when frame_pointer_needed is false? Jason
