[API] How to get the leftside of an expresstion?

Development
1

Assume I have an expresstion log_0.local.UB[i1.c] = tir.log(data.local.UB[i1.c]), I want to get its leftside part log_0.local.UB[i1.c], is there any api ?

(gdb) p tvm::Dump(op->value)
tir.log(data.local.UB[i1.c])
$37 = void
(gdb) p tvm::Dump(op)
log_0.local.UB[i1.c] = tir.log(data.local.UB[i1.c])

Now, the log_0.local.UB[i1.c] can be get with 2 independent part, .ie log_0.local.UB and i1.c, and their related api is op->buffer_var and op->index, but I still can’t get the whole log_0.local.UB[i1.c] directly.