Verify non-critical edges in OSSA #34635
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There are multiple reasons this is needed. 1. Most passes do not perform CFG transformations. However, we often need to split critical edges and remember to invalidate all SIL analyses at the end of virtually every pass. This is very innefficient and highly bug prone. 2. Many SIL analysis algorithms needs to reason about CFG edges. Avoiding critical edges leads to far simpler and more efficient designs when edges can be identified by blocks. 3. Handling block arguments on conditional branches create complexity at the lowest level of the SIL interface. This complexity is difficult to abstract over and bleeds until any algorithm that needs to reason about phi operands. It's far easier to work with phis if we can easily recover the phi operand with only a reference to the predecessor block. 4. Attempting to preserve critical edges in high and mid level IR blocks optimizations that otherwise have no business optimizing branches. Branch optimization should always be defered to machine level IR where the most relevant heuristics are employed to remove unconditional branches. If code didn't need to be placed on a critical edges, then a branch optimization can easily remove that code from the critical edge.
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This allows us to start cleaning up passes that do weird things with critical edges, as long as those passes are limited to OSSA. For example, CopyProgagation was broken in this respect. Now we can write simpler OSSA passes that deal with block arguments.
Also, we can now make a clear distinction between passes that modify the CFG and those that don't. This lets us do much better at preserving analysis results across passes.
Most importantly for me, it stops the onslaught of new .sil tests with critical edges which take a lot of time to rewrite later.