Benjamin Kramer 49064ff770 InstCombine: Add a combine that turns (2^n)-1 ^ x back into (2^n)-1 - x iff x is smaller than 2^n and it fuses with a following add.
This was intended to undo the sub canonicalization in cases where it's not profitable, but it also
finds some cases on it's own.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147256 91177308-0d34-0410-b5e6-96231b3b80d8
2011-12-24 17:31:53 +00:00
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