Re: Insn missing in Size optimization(-Os)

[daniel tian <daniel dot xntian at gmail dot com>]

Hi,
  Addition information, I just found. It was deleted in function: void
set_insn_deleted (rtx insn), in emit-rtl.c.
  It is called by reload() in reload1.c.
  Here is the code in reload():

/* If a pseudo has no hard reg, delete the insns that made the equivalence.
     If that insn didn't set the register (i.e., it copied the register to
     memory), just delete that insn instead of the equivalencing insn plus
     anything now dead.  If we call delete_dead_insn on that insn, we may
     delete the insn that actually sets the register if the register dies
     there and that is incorrect.  */

  for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
    {
      if (reg_renumber[i] < 0 && reg_equiv_init[i] != 0)
	{
	  rtx list;
	  for (list = reg_equiv_init[i]; list; list = XEXP (list, 1))
	    {
	      rtx equiv_insn = XEXP (list, 0);

	      /* If we already deleted the insn or if it may trap, we can't
		 delete it.  The latter case shouldn't happen, but can
		 if an insn has a variable address, gets a REG_EH_REGION
		 note added to it, and then gets converted into a load
		 from a constant address.  */
	      if (NOTE_P (equiv_insn)
		  || can_throw_internal (equiv_insn))
		;
	      else if (reg_set_p (regno_reg_rtx[i], PATTERN (equiv_insn)))
		delete_dead_insn (equiv_insn);
	      else
		SET_INSN_DELETED (equiv_insn);
	    }
	}
    }

But I don't know why the pseudo register can not be fit into a hard
register. The insn :

 (insn:HI 8 6 11 2 movebug.c:12 (set (reg/f:SI 42)
       (symbol_ref:SI ("fun") [flags 0x3] <function_decl 0xb729ba10
fun>)) 15 {symbolic_address_load} (expr_list:REG_EQUIV (symbol_ref:SI
("fun") [flags 0x3] <function_decl 0xb729ba10 fun>)
       (nil)))

is obvious a very useful insn, not a dead one.

So does anybody know why.
Thanks very much.

 daniel.tian