This commit extends the CompactCompatibleArrays DLAStep to also consider
non-strided accesses.
Strided accesses are still always considered first, and they are still
considered the only real source of information on arrays, but after
having tried to compact all the compatible arrays,
CompactCompatibleArrays now also considers non-strided instance edges to
see if they can be compacted with the rest of the inferred array.
This has shown to handle gracefully a number of real-world examples and
reduce unions.
Before this commit, the CompactCompatibleArray DLAStep had that caused
the compaction to be sensible to the order of the pairs of edges that
were compacted, and that also caused the compaction operation to overrun
the end of the containing struct in some corner cases.
This commit fixes both bugs.
Now the compaction routine is not ordering-sensitive anymore.
For each pair of edges <A, B> to compact it tries to compact them in 2
possible ways: by aligning A to B shifting A to lower offsets, and by
aligning B to A shifting B to lower offsets.
If both succeed, it picks the best result among the two, which doesn't
depend on the ordering of A and B.
This fixes the order-sensitiveness.
While reworking this logic, the logic was fixed so that if any of the
two compaction attempts causes to overrun the end of the containing
struct, the attempt is not considered successful anymore, and it's
discarded altogether.
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.
Alessandro Di Federico