[Bug target/50358] New: AVR: Implement [u]maddqihi4 [u]msubqihi4 patterns on the enhanced core

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50358

             Bug #: 50358
           Summary: AVR: Implement [u]maddqihi4 [u]msubqihi4 patterns on
                    the enhanced core
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: g...@gcc.gnu.org
                CC: eric.wedding...@atmel.com
            Target: avr


avr-gcc 4.6.1 -Os -mmcu=atmega8 translates the following test function

int madd_x (int i, char a, char b)
{
    return i + a*b;
}

to

    muls r22,r20     ;  10    mulqihi3
    movw r20,r0
    clr r1
    add r20,r24     ;  11    *addhi3/1
    adc r21,r25
    movw r24,r20     ;  31    *movhi/1

where it could be

    muls r22,r20     ;  *maddqihi4/1
    add r24,r0
    adc r25,r1
    clr r1

instead i.e. the addition can be done in place and the product need not to be
moved out of R0, reducing code size and register pressure and increasing speed.