[PATCH] Make DAGCombiner work on vector bitshifts with constant splat vectors.

[Tim Northover]

  Hi Matt,

  Doesn't this convert a bunch of BUILD_VECTOR nodes into just CONSTANTs? I'm rather dubious that most backends will cope with that.

  It also seems to be missing the definition of getScalarSizeInBits. Does it depend on a completely internal patch, or just one that hasn't been committed yet?

  Cheers.

  Tim.

http://llvm-reviews.chandlerc.com/D2997