private void computeCanBeAvail(final ExprInfo exprInfo) {
		final Iterator blocks = cfg.nodes().iterator();

		while (blocks.hasNext()) {
			final Block block = (Block) blocks.next();

			final Phi phi = exprInfo.exprPhiAtBlock(block);

			if (phi == null) {
				continue;
			}

			if (!phi.downSafe() && phi.canBeAvail()) {
				resetCanBeAvail(exprInfo, phi);
			}
		}
	}