8b75671314
This is almost the same as the abandoned D48529, but it allows splat vector constants too. This replaces the x86-specific code that was added with the alternate patch D48557 with the original generic combine. This transform is a less restricted form of an existing InstCombine and the proposed SDAG equivalent for that in D128080: https://alive2.llvm.org/ce/z/OUm6N_ Differential Revision: https://reviews.llvm.org/D128123