why allocation scope is introduced ?

Hi,
I looked into https://github.com/intel/graph-compiler/blob/ef3d150ad591dc9ff3c86686341c2e7ce007695d/docs/memref_schedule.md and understood how allocator works.

But i don't understand why allocation scope is introduced.
Here is dupmed IR,
```
func.func @nested_forall(%arg0: memref<2xf32>) attributes {__mergealloc_scope = 94435173533712 : i64} {
%c0 = arith.constant 0 : index
%c2 = arith.constant 2 : index
%c4 = arith.constant 4 : index
%c16 = arith.constant 16 : index
%alloc = memref.alloc() {__mergealloc_lifetime = array} : memref<2xf32>
memref.copy %arg0, %alloc : memref<2xf32> to memref<2xf32>
scf.forall (%arg1) = (%c0) to (%c16) step (%c2) {
%alloc_0 = memref.alloc() {__mergealloc_lifetime = array} : memref<4xf32>
%alloc_1 = memref.alloc() {__mergealloc_lifetime = array} : memref<8xf32>
scf.forall (%arg2) in (%c4) {
"test.source"(%alloc) : (memref<2xf32>) -> ()
"test.source"(%alloc_1) : (memref<8xf32>) -> ()
%alloc_2 = memref.alloc() {__mergealloc_lifetime = array} : memref<16xf32>
"test.source"(%alloc_2) : (memref<16xf32>) -> ()
} {__mergealloc_scope = 94435173605248 : i64}
"test.source"(%alloc) : (memref<2xf32>) -> ()
"test.source"(%alloc_0) : (memref<4xf32>) -> ()
} {__mergealloc_scope = 94435173478560 : i64}
return
}
```
there are 3 allocation scopes.

However, there is only 1 physical memory.
so i expect there is only 1 memref.alloc op in the whole IR.
is it reasonable?

Hope some one can help me out.
Thank you very Much!