how it started:

(set (reg:CC 136)
        (compare:CC (reg:DI 151 [+8 ])
            (const_int 0 [0x0]))) 464 {*cmpdi_internal1} (nil))


what was tried:

(set (reg:CC 136)
        (compare:CC (neg:DI (reg:DI 149 [ a+8 ]))
            (const_int 0 [0x0]))) -1 (nil))


what it became:

(parallel [
            (set (reg:CC 136)
                (compare:CC (neg:DI (reg:DI 149 [ a+8 ]))
                    (const_int 0 [0x0])))
            (clobber (scratch:DI))
        ]) 105 {*rs6000.md:2102} (nil))


what it was "restored" as:

(parallel [
            (set (reg:CC 136)
                (compare:CC (reg:DI 151 [+8 ])
                    (const_int 0 [0x0])))
            (clobber (scratch:DI))
        ]) 464 {*cmpdi_internal1} (nil))