Enabling -combiner-global-alias-analysis does find better chains and
therefore can result in prohibitively large compile times for very large
This patch protects against large blocks without hurting the expected behaviour
for reasonable sizes. The typical use case for merging is when the stores to be
merged are reasonably local (e.g. when merging 4 stores, these 4 stores can be
found within a window of not much more than 4 unrelated store instructions).