[PATCH] D14043: [bugpoint] Add a named metadata (+their operands) reducer

[Pete Cooper via llvm-commits]

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Philip has been doing most of the reviewing, so I'll defer to him for a final LGTM.  But FWIW, this LGTM given the work to address his feedback.

BTW, my approach was a little different.  You are reducing the number of CU's which is great.  I should have tried that first.

My approach was to reduce the number of types, global variables, imported entities, and subprograms in an individual CU.  Given that these tend to also be referenced from llvm.dbg.* intrinsics, many dbg info entries would remain in the metadata, even after being removed from the CU.  From there, I would then strip dbg info from instructions and see if there was a reduced set which would still crash.  Eventually I'd get the smallest possible CU in terms of types, subprograms, etc, which demonstrate the bug.

Unfortunately, this didn't seem to be 100% reliable.  I kept encountering crashes in llc when it tried to emit the debug info as it thought entries were missing, or weren't in states it wanted them to be in.  So I may have actually found real bugs, i'm not sure, but those bugs made it impossible to run llc in bug point and know that the crashes were the original bug and not what i was causing with reduced debug info.

Anyway, i still have the patch lying around if its ever of interest.  Its about 6 months old though so likely needs fixed to work on ToT.


Repository:
  rL LLVM

http://reviews.llvm.org/D14043