[Bug other/31043] duplicated data in .rodata / .rodata.cst sections.

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from ubizjak at gmail dot com  2009-10-28 22:27 -------
(In reply to comment #3)

> > And this constant is handled in different way than its shadow in the memory.
> 
> could you explain why? they are identicial constants.
> -fmerge-constants should do something with this.

The load of constant into the register is expanded through ix86_expand_move in
"movdf" expander.  There we have:

      if (can_create_pseudo_p ()
          && FLOAT_MODE_P (mode)
          && GET_CODE (op1) == CONST_DOUBLE)
        {
          /* If we are loading a floating point constant to a register,
             force the value to memory now, since we'll get better code
             out the back end.  */

          op1 = validize_mem (force_const_mem (mode, op1));
          if (!register_operand (op0, mode))
            {
              rtx temp = gen_reg_rtx (mode);
              emit_insn (gen_rtx_SET (VOIDmode, temp, op1));
              emit_move_insn (op0, temp);
              return;
            }
        }

So, the trick would be to find the same FP constants in memory and load from
there.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31043