Before this commit, the dla::Step CompactCompatibleArrays was
occasionally generating artificial nodes that were larger than the inner
data, forcing their size to Stride - AvailableSlack.
This commit fixes the problem keeping track of the actual size that is
consumed in the array element, and forcing the size of the artificial
nodes to that.
Before this commit, a logic mistake made the AvailableSlack too large
for arrays that started near the beginning of their parent.
This in turn allowed a compacted array to "underflow" on lower addresses
w.r.t. the parent.
This commit fixes the problem by properly computing the AvailableSlack,
restraining it in cases where the array under analysis is close to the
beginning of the parent.
Pietro Fezzardi