Re: Insn missing in Size optimization(-Os)

[daniel tian <daniel.xntian@gmail.com>]

>
> You might start by monitoring emit_reload_insns's behavior when it handles
> your insn.
I just debug the source code with your advice. Check the function
emit_reload_insns.

That insn was deleted before entering funcion emit_reload_insns. It
was deleted in reload(...) in reload1.c file just before calling
function reload_as_needed(this function will call emit_reload_insns).
It is sure that the insn is generated, but deleted after reload.

insn was deleted in following code.
/* 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);                 ---->>>>>>>> Call
this function to delete insn.
	      else
		SET_INSN_DELETED (equiv_insn);
	    }
	}
    }

I don't know where the  reg_equiv_init[i], reg_renumber[i] exactly
changed. I knew the init reg_renumber array is to be -1.
where those arrays' value changed and by what criteria.

I mean I don't know where the gcc thinks this insn is dead, and why dead.


Thanks for your advice.