  In this paper, we consider passive RIS-assisted multi-user communication
between wireless nodes to improve the blocked line-of-sight (LOS) link
performance. The wireless nodes are assumed to be equipped with Massive
Multiple-Input Multiple-Output antennas, hybrid precoder, combiner, and
low-resolution analog-to-digital converters (ADCs). We first derive the
expression for the Cramer-Rao lower bound (CRLB) of the Mean Squared Error
(MSE) of the received and combined signal at the intended receiver under
interference. By appropriate design of the hybrid precoder, combiner, and RIS
phase settings, it can be shown that the MSE achieves the CRLB. We further show
that minimizing the MSE w.r.t. the phase settings of the RIS is equivalent to
maximizing the throughput and energy efficiency of the system. We then propose
a novel Information-Directed Branch-and-Prune (IDBP) algorithm to derive the
phase settings of the RIS. We, for the first time in the literature, use an
information-theoretic measure to decide on the pruning rules in a tree-search
algorithm to arrive at the RIS phase-setting solution, which is vastly
different compared to the traditional branch-and-bound algorithm that uses
bounds of the cost function to define the pruning rules. In addition, we
provide the theoretical guarantees of the near-optimality of the RIS
phase-setting solution thus obtained using the Asymptotic Equipartition
property. This also ensures near-optimal throughput and MSE performance.
