[PATCH] D136109: llvm-reduce: Add conditional reduction passes

[Matt Arsenault via Phabricator via llvm-commits]

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Copy this technique from bugpoint. Before trying to blindly
delete blocks, try to fold branch conditions. This intuitively
 makes more sense for a faster reduction, since you can find
dead paths in the function to prune out before trying to bisect
blocks in source order.

      

Seems to provide some speedup on my multi-hour reduction samples.

      

This does have the potential to produce testcases with unreachable
blocks. This is already a problem with the existing block
reduction pass. I'm struggling dealing with invalid reductions
in these cases, so in the future this should probably start
deleting those. However, I do sometimes try to reduce failures
in code that becomes unreachable, so I'm not totally sure
what to do here.


https://reviews.llvm.org/D136109

Files:
  llvm/test/tools/llvm-reduce/reduce-conditionals.ll
  llvm/tools/llvm-reduce/DeltaManager.cpp
  llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp
  llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.h

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