Re: [PATCH]: Fix PR debug/19124

[Richard Henderson <rth at redhat dot com>]

On Mon, Dec 27, 2004 at 09:27:08PM -0500, Daniel Berlin wrote:
> The dwarf3 standard says we can't have location list entries where the 
> begin and end addresses are the same (except for the list terminator 
> entry, which is begin == 0 && end == 0).

What a suck-ass rule.  Because,

> +/* Return the first previous insn of INSN that is a non-note and non-label
> +   (except for note_var_location's).  */
> +
> +static rtx
> +prev_regular_or_varloc_insn (rtx insn)
> +{
> +  while (insn)
> +    {
> +      insn = PREV_INSN (insn);
> +      if (!insn 
> +	  || (NOTE_P (insn)
> +	      && NOTE_LINE_NUMBER (insn) == NOTE_INSN_VAR_LOCATION))
> +	break;
> +      if (NOTE_P (insn) || LABEL_P (insn))
> +	continue;
> +      break;
> +    }
> +  return insn;
> +}

All this tells you is that there's an insn.  It doesn't say that the
insn expands to a non-zero number of assembly instructions.  E.g.

	asm ("" : "=r" (x)  :"0"(x));

which has legitimate uses.  There are also insns that the backend
expands to zero instructions that exist to keep the optimizer happy.

But I guess there's not a whole lot you can do about this.


r~