On Fri, Dec 20, 2019 at 12:29 AM Jakub Jelinek <ja...@redhat.com> wrote:
>
> Hi!
>
> The following patch optimizes
> decl %eax; cmpl $-1, %eax; jne .Lxx;
> into shorter and even possible to be fused:
> subl $1, %eax; jnc .Lxx;
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, during which
> this peephole2 triggered 7825 times, ok for trunk?
>
> 2019-12-19 Jakub Jelinek <ja...@redhat.com>
>
> PR target/93002
> * config/i386/i386.md (dec reg; cmp $-1, reg; jne lab): New
> define_peephole2.
>
> * gcc.target/i386/pr93002.c: New test.
OK.
Thanks,
Uros.
> --- gcc/config/i386/i386.md.jj 2019-12-17 21:39:26.686939030 +0100
> +++ gcc/config/i386/i386.md 2019-12-19 13:31:52.424108730 +0100
> @@ -6503,6 +6503,36 @@ (define_peephole2
> [(set (reg:CC FLAGS_REG)
> (compare:CC (match_dup 0) (match_dup 1)))])
>
> +;; decl %eax; cmpl $-1, %eax; jne .Lxx; can be optimized into
> +;; subl $1, %eax; jnc .Lxx;
> +(define_peephole2
> + [(parallel
> + [(set (match_operand:SWI 0 "general_reg_operand")
> + (plus:SWI (match_dup 0) (const_int -1)))
> + (clobber (reg FLAGS_REG))])
> + (set (reg:CCZ FLAGS_REG)
> + (compare:CCZ (match_dup 0) (const_int -1)))
> + (set (pc)
> + (if_then_else (match_operator 1 "bt_comparison_operator"
> + [(reg:CCZ FLAGS_REG) (const_int 0)])
> + (match_operand 2)
> + (pc)))]
> + "peep2_regno_dead_p (3, FLAGS_REG)"
> + [(parallel
> + [(set (reg:CC FLAGS_REG)
> + (compare:CC (match_dup 0) (const_int 1)))
> + (set (match_dup 0)
> + (minus:SWI (match_dup 0) (const_int 1)))])
> + (set (pc)
> + (if_then_else (match_dup 3)
> + (match_dup 2)
> + (pc)))]
> +{
> + rtx cc = gen_rtx_REG (CCmode, FLAGS_REG);
> + operands[3] = gen_rtx_fmt_ee (GET_CODE (operands[1]) == NE
> + ? GEU : LTU, VOIDmode, cc, const0_rtx);
> +})
> +
> (define_insn "*subsi_3_zext"
> [(set (reg FLAGS_REG)
> (compare (match_operand:SI 1 "register_operand" "0")
> --- gcc/testsuite/gcc.target/i386/pr93002.c.jj 2019-12-19 13:49:43.885341492
> +0100
> +++ gcc/testsuite/gcc.target/i386/pr93002.c 2019-12-19 13:50:46.465361213
> +0100
> @@ -0,0 +1,22 @@
> +/* PR target/93002 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +/* { dg-final { scan-assembler-not "cmp\[^\n\r]*-1" } } */
> +
> +volatile int sink;
> +
> +void
> +foo (void)
> +{
> + unsigned i = 1000;
> + while (i--)
> + sink = i;
> +}
> +
> +void
> +bar (void)
> +{
> + int i = 2000;
> + while (i--)
> + sink = i;
> +}
>
> Jakub
>
