This commit enables ArrangeAccessesHierachically to push down pointer
edges when rearranging accesses hierarchically.
In particular, if an edge N is being pushed down another edge M, and M
is at offset 0, and N reaches a pointer edge PE that points to a
grandparent G of M at offset 0, then we want to push down the pointer
edge PE so that it points to the target of M, unless there is another
edge M' different from M, such that M' has the same properties of M but
target(M) != target(M').
Before this commit, ArrangeAccesseHierachically was removing nodes from
the graph, instead of merging them.
This degraded the information collected on the graph useful for debug.
This commit drops the use of removeNode method, and switches to using
mergeNodes, that preserves the useful debug information when merging.
Before this commit we were using int64_t for Offset, Strides, and
TripCounts.
Originally, this choice was intended because for some time we envisioned
actually having a use for negative values, but in the end we decided
there's no use for those.
This commit switches all to unsigned integers, allowing to remove some
static_cast across the codebase, and overall easing typicall computation
we have to perform on those fields.
Pietro Fezzardi