r-indexing without backward searching

Suppose we are given a text $T$ of length $n$ and a straight-line program for $T$ with $g$ rules. Let $\bar{r}$ be the number of runs in the Burrows-Wheeler Transform of the reverse of $T$. We can index $T$ in $O (\bar{r} + g)$ space such that, given a pattern $P$ and constant-time access to the Karp-Rabin hashes of the substrings of $P$ and the reverse of $P$, we can find the maximal exact matches of $P$ with respect to $T$ correctly with high probability and using $O (\log n)$ time for each edge we would descend in the suffix tree of $T$ while finding those matches.