8df93ce455
This patch transforms truncation between vectors of integers into X86ISD::PACKUS/PACKSS operations during DAG combine. We don't do it in lowering phase because after type legalization, the original truncation will be turned into a BUILD_VECTOR with each element that is extracted from a vector and then truncated, and from them it is difficult to do this optimization. This greatly improves the performance of truncations on some specific types. Cost table is updated accordingly. Differential revision: http://reviews.llvm.org/D14588 llvm-svn: 256194