[Bug target/82182] New: m68k slow code: u16/u8 division calls divsi3

[cand at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82182

            Bug ID: 82182
           Summary: m68k slow code: u16/u8 division calls divsi3
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cand at gmx dot com
  Target Milestone: ---

C:
#include <stdint.h>

uint16_t mydiv(const uint16_t a, const uint8_t b) {
        return a / b;
}

uint16_t mydiv2(const uint16_t a, const uint16_t b) {
        return a / b;
}


Assembly:
#NO_APP
        .file   "kai.c"
        .globl  __udivsi3
        .globl  __divsi3
        .text
        .align  2
        .globl  mydiv
        .type   mydiv, @function
mydiv:
        moveq #0,%d0
        move.w 6(%sp),%d0
        moveq #0,%d1
        move.b 11(%sp),%d1
        move.l %d1,-(%sp)
        move.l %d0,-(%sp)
        jsr __divsi3
        addq.l #8,%sp
        rts
        .size   mydiv, .-mydiv
        .align  2
        .globl  mydiv2
        .type   mydiv2, @function
mydiv2:
        move.w 6(%sp),%d0
        and.l #0xFFFF,%d0
        divu.w 10(%sp),%d0
        rts
        .size   mydiv2, .-mydiv2
        .ident  "GCC: (GNU) 7.2.0"


The hardware division is several times faster than divsi3. Further, I'm baffled
as to why gcc turns the unsigned division to signed, as udivsi3 would be faster
than divsi3.