What is the Use of "Implicit EFLAGS" in TableGen


     In the Table Gen format of defining Instructions for X86 architecture, some of the instruction patterns has both the dag expression "(implicit EFLAGS)" as well as the definition "Defs = [EFLAGS]". What is the difference between these two? Cant the Instruction Selector consider the Defs list when doing pattern match. I am confused when to use (implicit EFLAGS) expression.