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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/65164] New: [5 Regression][SH] missed subc in integer sign function
Date: Sun, 22 Feb 2015 16:51:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65164

            Bug ID: 65164
           Summary: [5 Regression][SH] missed subc in integer sign
                    function
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
            Target: sh*-*-*

These are integer sign functions taken from a book.
For some of them the code got worse after the introduction of the treg_set_expr
stuff.

int signfunc_00 (int x)
{
  return (x >> 31) | ((unsigned int)(-x) >> 31);
}


int signfunc_01 (int x)
{
  return -((unsigned int)x >> 31) | ((unsigned int)(-x) >> 31);
}


int signfunc_02 (int x)
{
  return (x > 0) - (x < 0);
}

4.9:
        cmp/pl  r4
        movt    r0
        shll    r4
        movt    r4
        rts
        sub     r4,r0

trunk:
        mov     r4,r1
        shll    r1
        movt    r1
        cmp/pl  r4
        movt    r0
        rts
        sub     r1,r0


int signfunc_03 (int x)
{
  return (x >= 0) - (x <= 0);
}

4.9:
        cmp/pz  r4
        mov     #0,r1
        movt    r0
        cmp/ge  r4,r1
        rts
        subc    r1,r0

trunk:
        mov     #0,r1
        cmp/ge  r4,r1
        movt    r1
        cmp/pz  r4
        movt    r0
        rts
        sub     r1,r0

It seems that this requires a pattern like

(set (match_operand:SI 0 "arith_reg_dest")
     (minus:SI (match_operand 1 "treg_set_expr")
               (match_operand 2 "treg_set_expr")))


For signfunc_02, combine is looking for the pattern:

Failed to match this instruction:
(set (reg:SI 169 [ D.1518 ])
    (minus:SI (gt:SI (reg/v:SI 168 [ x ])
            (const_int 0 [0]))
        (lshiftrt:SI (reg/v:SI 168 [ x ])
            (const_int 31 [0x1f]))))

For signfunc_03, combine is looking for the pattern:
(set (reg:SI 169 [ D.1522 ])
    (minus:SI (ge:SI (reg:SI 4 r4 [ x ])
            (const_int 0 [0]))
        (le:SI (reg:SI 4 r4 [ x ])
            (const_int 0 [0]))))



On SH, it seems that the insn sequence
        cmp/pz  r4
        mov     #0,r1
        movt    r0
        cmp/ge  r4,r1
        subc    r1,r0

is the best to realize an integer sign function.  So actually all the functions
above should be converted into the same sequence.