[CycleAnalysis] Methods to verify cycles and their nesting.

[ssahasra]

[CycleAnalysis] Methods to verify cycles and their nesting.

The original implementation provided a simple method to check whether the forest
of nested cycles is well-formed. This is now augmented with other methods to
check well-formedness of every cycle, either invdividually, or as the entire
forest. These will be used by future transforms that modify CycleInfo.

[Transforms] Refactor CreateControlFlowHub

CreateControlFlowHub is a method that redirects control flow edges from a set of
incoming blocks to a set of outgoing blocks through a new set of "guard" blocks.
This is now refactored into a separate file with one enhancement: The input to
the method is now a set of branches rather than two sets of blocks.

The original implementation reroutes every edge from incoming blocks to outgoing
blocks. But it is possible that for some incoming block InBB, some successor S
might be in the set of outgoing blocks, but that particular edge should not be
rerouted. The new implementation makes this possible by allowing the user to
specify the targets of each branch that need to be rerouted.

This is needed when improving the implementation of FixIrreducible #101386. Current
uses in FixIrreducible and UnifyLoopExits do not demonstrate this finer control
over the edges being rerouted.

[ssahasra]

• [CycleAnalysis] Methods to verify cycles and their nesting. #103006 👈
• main

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