[Bug rtl-optimization/47008] [4.6 Regression] gfortran.dg/extends_{23}.f03 FAIL with -Os -fschedule-insns

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47008

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |law at gcc dot gnu.org,
                   |                            |vmakarov at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> 2010-12-20 11:10:00 UTC ---
The note is added in update_equiv_regs called from ira.
          /* cse sometimes generates function invariants, but doesn't put a
             REG_EQUAL note on the insn.  Since this note would be redundant,
             there's no point creating it earlier than here.  */
          if (! note && ! rtx_varies_p (src, 0))
            note = set_unique_reg_note (insn, REG_EQUAL, copy_rtx (src));
...
          /* If this register is known to be equal to a constant, record that
             it is always equivalent to the constant.  */
          if (DF_REG_DEF_COUNT (regno) == 1
              && note && ! rtx_varies_p (XEXP (note, 0), 0))
            {
              rtx note_value = XEXP (note, 0);
              remove_note (insn, note);
              set_unique_reg_note (insn, REG_EQUIV, note_value);
            }
This is correct at that point, because note_value is frame - 48, which really
is constant through the whole function.

But when
  /* If we changed something, perform elimination in REG_NOTES.  This is
     needed even when REPLACE is zero because a REG_DEAD note might refer
     to a register that we eliminate and could cause a different number  
     of spill registers to be needed in the final reload pass than in
     the pre-passes.  */
  if (val && REG_NOTES (insn) != 0)
    REG_NOTES (insn)
      = eliminate_regs_1 (REG_NOTES (insn), VOIDmode, REG_NOTES (insn), true,
                          false);
in eliminate_regs_in_insn changes the REG_EQUIV note content from frame -
something to %rsp + something, the expression is suddenly not constant anymore.

So, shouldn't eliminate_regs_1 here downgrade REG_EQUIV notes where
!rtx_varies_p before and rtx_varies_p afterwards to REG_EQUAL?