[PATCH] D37957: [TableGen] Some simple optimizations to TableGen execution time

[Zachary Turner via Phabricator via llvm-commits]

zturner created this revision.
Herald added a subscriber: igorb.

I got sufficiently annoyed with sitting around waiting forever for TableGen to complete during a build, so I profiled it.  While there's quite a bit more that can be done, this is the really easy stuff.  Tons of string allocations and re-allocations, STL stringstream usage, and STL set container usage.

With this patch, X86GenDAGISel is reduced from ~45 seconds to ~33 seconds on my machine, which is a ~1.3x speedup.

The next biggest bottleneck is the class that indents and formats the output.  Given that tablegen output is really only intended to be consumed by a machine, it makes sense to question whether or not it's worth the performance cost.  I removed the formatting and my speedup jumps to a 2x speedup (44s -> 22s).

After I get the single-threaded execution time sufficiently fast, I might even try to parallelize it.  It seems like a terribly obvious and easy candidate for parallelization given that we now have simple parallel algorithms in Support.

Feel free to add other reviewers if there's someone better.


https://reviews.llvm.org/D37957

Files:
  llvm/utils/TableGen/CodeGenDAGPatterns.cpp
  llvm/utils/TableGen/CodeGenDAGPatterns.h

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