does the instruction combiner regards (foo & 0xff) as a special case?

[ibanez@sunplus.com]

You are cool, now I found a

(set (reg:CC_Z 33 cc)
    (compare:CC_Z (zero_extend:SI (subreg:QI (reg/v:SI 166 [ a ]) 0))
        (const_int 0 [0x0])))

It's what I'm looking for.

Thank you so much.