Add peephole for -Os lock; dec (PR target/70821)

Hi!

Optimizing atomic_fetch_add followed by comparison into just testing
the flags of the lock; sub is handled by a peephole2, which works usually
fine, except that for -Os we have another peephole2 that transforms
movl $-1, %reg into orl $-1, %reg and that causes the above mentioned
peephole2 not to trigger anymore.

Fixed by adding a peephole2 even for this case.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-04-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/70821
	* config/i386/sync.md (define_peephole2 *atomic_fetch_add_cmp<mode>):
	Add new peephole2 where the first insn is *mov<mode>_or instead of
	*mov<mode>_internal.

	* gcc.target/i386/pr70821.c: New test.


	Jakub

On Thu, Apr 28, 2016 at 5:42 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> Optimizing atomic_fetch_add followed by comparison into just testing
> the flags of the lock; sub is handled by a peephole2, which works usually
> fine, except that for -Os we have another peephole2 that transforms
> movl $-1, %reg into orl $-1, %reg and that causes the above mentioned
> peephole2 not to trigger anymore.
>
> Fixed by adding a peephole2 even for this case.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2016-04-28  Jakub Jelinek  <jakub@redhat.com>
>
>         PR target/70821
>         * config/i386/sync.md (define_peephole2 *atomic_fetch_add_cmp<mode>):
>         Add new peephole2 where the first insn is *mov<mode>_or instead of
>         *mov<mode>_internal.
>
>         * gcc.target/i386/pr70821.c: New test.

OK.

Thanks,
Uros.

>
> --- gcc/config/i386/sync.md.jj  2016-01-04 14:55:56.000000000 +0100
> +++ gcc/config/i386/sync.md     2016-04-28 09:40:28.265764880 +0200
> @@ -467,6 +467,36 @@ (define_peephole2
>                    (plus:SWI (match_dup 1)
>                              (match_dup 2)))])])
>
> +;; Likewise, but for the -Os special case of *mov<mode>_or.
> +(define_peephole2
> +  [(parallel [(set (match_operand:SWI 0 "register_operand")
> +                  (match_operand:SWI 2 "constm1_operand"))
> +             (clobber (reg:CC FLAGS_REG))])
> +   (parallel [(set (match_dup 0)
> +                  (unspec_volatile:SWI
> +                    [(match_operand:SWI 1 "memory_operand")
> +                     (match_operand:SI 4 "const_int_operand")]
> +                    UNSPECV_XCHG))
> +             (set (match_dup 1)
> +                  (plus:SWI (match_dup 1)
> +                            (match_dup 0)))
> +             (clobber (reg:CC FLAGS_REG))])
> +   (set (reg:CCZ FLAGS_REG)
> +       (compare:CCZ (match_dup 0)
> +                    (match_operand:SWI 3 "const_int_operand")))]
> +  "peep2_reg_dead_p (3, operands[0])
> +   && (unsigned HOST_WIDE_INT) INTVAL (operands[2])
> +      == -(unsigned HOST_WIDE_INT) INTVAL (operands[3])
> +   && !reg_overlap_mentioned_p (operands[0], operands[1])"
> +  [(parallel [(set (reg:CCZ FLAGS_REG)
> +                  (compare:CCZ
> +                    (unspec_volatile:SWI [(match_dup 1) (match_dup 4)]
> +                                         UNSPECV_XCHG)
> +                    (match_dup 3)))
> +             (set (match_dup 1)
> +                  (plus:SWI (match_dup 1)
> +                            (match_dup 2)))])])
> +
>  (define_insn "*atomic_fetch_add_cmp<mode>"
>    [(set (reg:CCZ FLAGS_REG)
>         (compare:CCZ
> --- gcc/testsuite/gcc.target/i386/pr70821.c.jj  2016-04-28 09:56:06.239893613 +0200
> +++ gcc/testsuite/gcc.target/i386/pr70821.c     2016-04-28 09:55:23.000000000 +0200
> @@ -0,0 +1,16 @@
> +/* PR target/70821 */
> +/* { dg-do compile } */
> +/* { dg-options "-Os" } */
> +/* { dg-additional-options "-march=i686" { target ia32 } } */
> +
> +void bar (void);
> +
> +void
> +foo (int *p)
> +{
> +  if (__atomic_sub_fetch (p, 1, __ATOMIC_SEQ_CST))
> +    bar ();
> +}
> +
> +/* { dg-final { scan-assembler "lock;? dec" } } */
> +/* { dg-final { scan-assembler-not "lock;? xadd" } } */
>
>         Jakub