This patch implements the LKK algorithm for optimizing remainder computations with a constant divisor.
LKK is an improvement on the previously used Granlund-Montgomery-Warren approach.
- I added functions foldSREM and foldUREM in DAGCombiner.cpp to handle signed and unsigned remainders.
- Tests have been performed on x86 for every 8 bit signed and unsigned remainder operation.
- Tests for 32 bit signed remainders have been performed on a large set of random integers.
- I also added some llc code gen tests.
- I am a bit unsure whether my isOperationLegalOrCustomOrPromote checks are too strict.