[PATCH] Simplify n-ary adds by reassociation

[Jingyue Wu]

I previously tried performing this optimization in StraightLineStrengthReduce (http://reviews.llvm.org/D8898), but realized it is probably worth a standalone pass for the following reasons:

1. it is general enough;
2. users can flexibly choose where to run it;
3. it can be made more efficient without being restricted to the framework of SLSR.

So, I gave it another try, and would like to see how you like this implementation. As mentioned in the header comments, this implementation is preliminary and has lots of limitations. But I hope to make it more fully-fledged iteratively. For now, I only plan to use it after SLSR in the NVPTX backend.


http://reviews.llvm.org/D8950

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