[Bug target/67057] New: [SH] Use negc to calculate 1-T+const_int

[Bug target/67057] New: [SH] Use negc to calculate 1-T+const_int

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67057

            Bug ID: 67057
           Summary: [SH] Use negc to calculate 1-T+const_int
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
  Target Milestone: ---

The following

int foo (int a, int b)
{
 return ((a & (1 << 25)) ? 5 : 4);
}

compiled with -O2 results in:

        mov.l   .L4,r1
        mov     #-1,r0
        tst     r1,r4
        negc    r0,r0
        rts     
        add     #4,r0    // r0 = 1 - T + 4
                         //    = 5 - T
.L5:
        .align 2
.L4:
        .long   33554432

The negc insn calculates 0 - reg - T, which can be used to calculate const_int
+ T.  In fact, it is already used to calculate 1 - T as a replacement for SH2A
movrt.

The resulting code should look something like this:
        mov.l   .L4,r1
        mov     #-5,r0
        tst     r1,r4
        rts
        negc    r0,r0


Combine is looking for a pattern:

Failed to match this instruction:
(set (reg:SI 162 [ D.1652 ])
    (plus:SI (zero_extract:SI (reg:SI 4 r4 [ a ])
            (const_int 1 [0x1])
            (const_int 25 [0x19]))
        (const_int 4 [0x4])))

Which could be implemented with treg_set_expr.

[Bug target/67057] [SH] Use negc to calculate 1-T+const_int

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67057

--- Comment #1 from Oleg Endo <olegendo at gcc dot gnu.org> ---
For some cases where T+const_int is calculated, like ...

int foo (int a, int b)
{
  return a == b ? 5 : 4;
}

comiled with -O2:
        cmp/eq  r5,r4
        movt    r0
        rts     
        add     #4,r0

.. the dependency of the comparison and the T bit store can be reduced:
        cmp/eq  r5,r4
        mov     #2,r0
        rts
        addc    r0,r0

This works only for even constants.

[Bug target/67057] [SH] Use negc to calculate 1-T+const_int

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67057

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #0)
> Combine is looking for a pattern:
> 
> Failed to match this instruction:
> (set (reg:SI 162 [ D.1652 ])
>     (plus:SI (zero_extract:SI (reg:SI 4 r4 [ a ])
>             (const_int 1 [0x1])
>             (const_int 25 [0x19]))
>         (const_int 4 [0x4])))
> 
> Which could be implemented with treg_set_expr.

In this case, the treg_set_expr should be only matched if it will expand into a
negating T bit store.  For that a new predicate "neg_treg_set_expr" should be
added.  sh_recog_treg_set_expr should get an additional parameter whether it
should match positive, negative or both forms.