llvm-project

d65be16a - [AArch64][GlobalISel] Add combine for build_vector(unmerge, unmerge, undef, undef) (#165539)

[AArch64][GlobalISel] Add combine for build_vector(unmerge, unmerge, undef, undef) (#165539) This PR adds a new combine to the `post-legalizer-combiner` pass. The new combine checks for vectors being unmerged and subsequently padded with `G_IMPLICIT_DEF` values by building a new vector. If such a case is found, the vector being unmerged is instead just concatenated with a `G_IMPLICIT_DEF` that is as wide as the vector being unmerged. This removes unnecessary `mov` instructions in a few places.