[PATCH] D78861: [Attributor] [WIP] Track AA dependency using dependency graph

[Kuter Dinel via Phabricator via llvm-commits]

kuter added a comment.

@bbn  Soo, I just realized that this way of implementing `GraphTraits` might be problematic with
graph iterators like (`scc_iterator`, `df_ iterator`) since they require a single entry point  to correctly handle
disconnected graphs and the `Attributor` dependencies are disconnected. Most disconnected graphs use a "synthetic node"
because of this.

I did not tested this but if we where to `df_iterator::begin(AA.DG)` you would iterate over nodes that you can reach
by following  the dependency edges of  the first `AbstractAttribute` that is inside . 
`GraphWriter` works well since it iterates over the nodes with `::nodes_start()` and `::nodes_end()`.

If you do not require looking across connected components in your own work we can merge this patch like this and
I can write a separate patch that fixes this issue when I need to use the `scc_iterator`.

Only solution I can find for this that don't increase memory consumption, is to move the dependency tracking out of the
`AbstractAttribute` into a class like `AADepNode` and  make `AbstractAttribute`  inherit dependency tracking from that class.
If we where to move `AllAbstractAttributes` into the "synthetic node"  we would have near zero memory overhead.

I know that this kinda like your initial implementation.  sorry for the inconvenience.


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