Before this commit, the MakeLayout step of the DLA used to deduplicate
structurally equal Layouts. This has turned out to be wrong when going
forward with the emission of types in C.
Being able to tell apart two different types that are structurally equal
is important for the emission of C types. Throwing this information away
with deduplication is bad. This commit disables such deduplication.
This commit prevents the creation of instance links for offsets that we
don't support yet, during the CreateIntraProceduralTypes DLAStep.
This makes possible to avoid explicitly handling those cases in many
DLASteps, such as ComputeUpperMemberAccess,
ComputeNonInterferingComponents, and DLAMakeLayouts.
The offsets that are not supported yet are:
- all negative offsets
- all strided offsets with non-strictly-positive stride values
- all strided offsets with non-strictly-positive stride values
- all strided offsets with known negative trip-count
Some beneficial side-effects of avoiding the creation of such links are:
- the total number of edges on the graph is reduced, reducing the worst
case depth of most visits
- it's impossible to create types with null or negative size (that we
wouldn't know how to emit in C)
Alvise de Faveri