[Bug target/47777] New: use __aeabi_idivmod to compute quotient and remainder at the same time

[carrot at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47777

           Summary: use __aeabi_idivmod to compute quotient and remainder
                    at the same time
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: car...@google.com
            Target: arm-eabi


Compile the following source code with options -march=armv7-a -O2

int t06(int x, int y)
{
  int a = x / y;
  int b = x % y;
  return a+b;
}

GCC 4.6 generates:

t06:
    @ args = 0, pretend = 0, frame = 0
    @ frame_needed = 0, uses_anonymous_args = 0
    stmfd    sp!, {r4, r5, r6, lr}
    mov    r6, r0
    mov    r5, r1
    bl    __aeabi_idiv
    mov    r1, r5
    mov    r4, r0
    mov    r0, r6
    bl    __aeabi_idivmod
    add    r0, r4, r1
    ldmfd    sp!, {r4, r5, r6, pc}

It calls function __aeabi_idiv to compute quotient and calls __aeabi_idivmod to
compute remainder. Actually __aeabi_idivmod can compute quotient and remainder
at the same time. By taking advantage of this we can simplify the code to

    push    {r4, lr}
    bl    __aeabi_idivmod
    add    r0, r0, r1
    pop    {r4, pc}