public void addPhi(final Block block) {
			Phi phi = phis[cfg.preOrderIndex(block)];

			if (phi == null) {
				if (StackPRE.DEBUG) {
					System.out.println("    add phi for " + def + " at "
							+ block);
				}

				phi = new Phi(block);
				phis[cfg.preOrderIndex(block)] = phi;
			}
		}