mov  r1, x
mov  r2, x
 and  r1, 7
mov  r3, r1
 cmp  r1, %tag
cmovne r2, lo_tag_map
 sub r3, 7
sar  r3, 31  ; -1 or 0 if tag=7
 sub r2, r1
mov  r4, [r2+r3*4+4]