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Subject: [Bug tree-optimization/59501] [4.9 Regression] Vector Gather with GCC 4.9 2013-12-08 Snapshot
Date: Thu, 19 Dec 2013 18:39:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59501

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to H.J. Lu from comment #2)
> (In reply to Jakub Jelinek from comment #1)
> >
> >   if (ix86_force_drap || !ACCUMULATE_OUTGOING_ARGS)
> >     crtl->need_drap = true;
> 
> They are needed for -m32.  Otherwise, we got
> 
> FAIL: g++.dg/torture/stackalign/eh-fastcall-1.C  -Os -fpic execution test
> FAIL: g++.dg/torture/stackalign/eh-global-1.C  -Os -fpic execution test
> FAIL: g++.dg/torture/stackalign/eh-inline-1.C  -Os -fpic execution test
> FAIL: g++.dg/torture/stackalign/eh-thiscall-1.C  -Os -fpic execution test

I'm not saying that ix86_get_drap_rtx should be changed.
But perhaps:
  /* If the only reason for frame_pointer_needed is that we conservatively
     assumed stack realignment might be needed, but in the end nothing that
     needed the stack alignment had been spilled, clear frame_pointer_needed
     and say we don't need stack realignment.  */
  if (stack_realign
      && !crtl->need_drap
      && frame_pointer_needed
      && crtl->is_leaf
      && flag_omit_frame_pointer
      && crtl->sp_is_unchanging
      && !ix86_current_function_calls_tls_descriptor
      && !crtl->accesses_prior_frames
      && !cfun->calls_alloca
      && !crtl->calls_eh_return
      && !(flag_stack_check && STACK_CHECK_MOVING_SP)
      && !ix86_frame_pointer_required ()
      && get_frame_size () == 0
      && ix86_nsaved_sseregs () == 0
      && ix86_varargs_gpr_size + ix86_varargs_fpr_size == 0)
in ix86_finalize_stack_realign_flags could be tweaked, not to bail out always
if we have !crtl->need_drap, because then it will be set pretty much for all
leaf functions.  I wonder if we can e.g. ask DF whether the drap reg is live at
entry, if it isn't live, supposedly we can clear crtl->need_drap or ignore it
for this purpose?  Also, I wonder even if we actually need the drap register we
can't for the leaf functions just avoid the dynamic realignment and simply let
the prologue set the drap reg to the right value.