[PATCH] rtx_writer: avoid printing trailing default values

[David Malcolm]

On Fri, 2016-11-04 at 19:53 +0100, Bernd Schmidt wrote:
> On 11/04/2016 08:14 PM, David Malcolm wrote:
> > 
> > With this, compact dumps omit the trailing (nil) for both regular
> > insns
> > and for JUMP_INSNs, and omits the surplus newline seen in my
> > earlier patch.
> > 
> > It also appears removes the trailing (nil) from expr_list.
> > 
> > Bootstrap&regrtest in progress.
> > 
> > OK for trunk if it passes?
> 
> This seems OK, with something left to be addressed perhaps in a
> followup:
> 
> > +	case JUMP_INSN:
> > +	  return JUMP_LABEL (in_rtx) == NULL_RTX;
> 
> Weren't we going to omit JUMP_LABELs in compact mode? If so, we'll
> need 
> a m_compact test here eventually as well.

We already omit JUMP_LABELs in compact mode, in
rtx_writer::print_rtx_operand_code_0, but we need this test to pass so
that we can potentially omit earlier (nil) operands in a JUMP_INSN e.g.
REG_NOTES.

Given that, perhaps this test should read:

	case JUMP_INSN:	

	  /* JUMP_LABELs are always omitted in compact mode, so treat
	     any value here as omittable, so that earlier operands can
	     potentially be omitted also.  */
	  return true;

or:

          return m_compact;

if we want to support calling operand_has_default_value_p in non
-compact mode.

OK with one of those changes?  (assuming successful testing)