[PATCH] D20178: Fix PR26055 - LiveDebugValues is very slow

[Adrian Prantl via llvm-commits]

aprantl updated this revision to Diff 57297.
aprantl added a comment.

This version replaces the data structures with SparseBitVectors and adds a couple of further optimizations.
Apart from making the algorithm much easier to read, this now brings the ASAN example I've been primarily testing on down to just 8 seconds(!) in a NoAsserts build (while producing an identical object file :-).

Some of the optimizations I added on top are:

- VarLoc now explicitly stores the register location for faster comparisons.
- transferDebugValue no longer checks the inlinedAt field. This makes a huge difference because looking up the inline scope of a MachineInstr is quite slow. This means that we can't propagate more than one inlined copies of the same variable. IMHO this is an acceptable trade-off. Note that this only affects accuracy, not correctness.
- I experimented with many different data structures (std::list, SmallDenseMap, SmallBitVector) for VarLocList, but settled on a SparseBitVector, because it makes the InLocs |= OpenRanges operation very natural. Iterating over the set bits in a SparseBitVector can be expensive, but it doesn't seem to make much of a difference in practice.

I think this is as far as I want to go with optimizations for PR26055.
Once we add support for more differnet kinds of debug (value) locations, it might make sense to revisit this.


http://reviews.llvm.org/D20178

Files:
  lib/CodeGen/LiveDebugValues.cpp
  test/DebugInfo/COFF/register-variables.ll
  test/DebugInfo/MIR/X86/live-debug-values-3preds.mir

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