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.
so that we can reduce away incidental parts of the CFG in cases where
the full simplifyCFG pass makes the test case uninteresting
Differential Revision: https://reviews.llvm.org/D131920
Matt Arsenault