RE: [PATCH] RL78 one_cmplhi2 improvement

["Sebastian Perta" <sebastian dot perta at renesas dot com>]

HI DJ,

> One thing to try is to use (subreg:QI in a define_expand, so that
> there's a one_cmplhi2 pattern that expands to two QImode insns that
> operate on HImode input/outputs via SUBREGs.

Thank you for the suggestion! After several attempts the following is the
only successful one, however the code produced is identical with and without
the patch:

(define_expand "one_cmplhi2"
 [(set (subreg:QI (match_operand:HI 0 "nonimmediate_operand") 0)
  (xor:HI (subreg:QI (match_operand:HI 1 "general_operand") 0)
  		(const_int -1)))
  (set (subreg:QI (match_dup 0) 1)
  (xor:HI (subreg:QI (match_dup 1) 1)
  		(const_int -1)))
  ]
  ""
  "DONE;"
)

Is this similar to what you had in mind?

Output code (same as before the patch ... the patch makes no difference):
_test_one_cmplhi:
	mov	a, [sp+4]
	xor	a, #-1
	mov	r8, a
	mov	a, [sp+5]
	xor	a, #-1
	mov	r9, a
	ret

I also explored other options including define_split without any success.

> If it doesn't work out, consider this patch approved, though.
Can I checkin now?

Best Regards,
Sebastian


> -----Original Message-----
> From: DJ Delorie [mailto:dj@redhat.com]
> Sent: 20 February 2018 19:39
> To: Sebastian Perta <Sebastian.Perta@renesas.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH] RL78 one_cmplhi2 improvement
> 
> 
> Const type promotion is the bane of embedded developers...
> 
> One thing to try is to use (subreg:QI in a define_expand, so that
> there's a one_cmplhi2 pattern that expands to two QImode insns that
> operate on HImode input/outputs via SUBREGs.
> 
> I don't have high hopes of gcc optimizing this properly in all cases,
> but it's worth trying.
> 
> If it doesn't work out, consider this patch approved, though.
> 
> Thanks!