GCNRegBankReassign pass issue

why amdgpu backend Drop the GCNRegBankReassign pass ?
if we can resolve reg bank conflict, some stall cycle may not happen.
in theory,resolve bank conflict can avoid some stall cycles per instruction。so i don’t understand why we can not get better performance with that pass.
follow nv programming guid, we can get better performance after ptxas resolve bank conflict.