question: private void clearRegisters ( Instruction start , Instruction end ) { for ( Instruction p = start ; ; p = p . nextInstructionInCodeOrder ( ) ) { for ( Enumeration < Operand > ops = p . getOperands ( ) ; ops . hasMoreElements ( ) ; ) { Operand op = ops . nextElement ( ) ; if ( op instanceof RegisterOperand ) { RegisterOperand rOp = ( RegisterOperand ) op ; clearDepGraphNodeForRegister ( rOp . getRegister ( ) ) ; } } if ( p == end ) break ; } for ( Enumeration < Register > e = GenericPhysicalDefUse . enumerateAllImplicitDefUses ( ir ) ; e . hasMoreElements ( ) ; ) { Register r = e . nextElement ( ) ; clearDepGraphNodeForRegister ( r ) ; } }
target:  Initialize (clear) the dNode field in Register for all registers in this basic block by setting them to null. Handles both explicit and implict use/defs.