The LIT test cases were migrated with the script provided by
Nikita Popov.
No manual changes were made. Committed without review since
no functional changes, after consultation with uweigand.
Instead of doing multiple unpacks when zero extending vectors (e.g. v2i16 ->
v2i64), benchmarks have shown that it is better to do a VPERM (vector
permute) since that is only one sequential instruction on the critical path.
This patch achieves this by
1. Expand ZERO_EXTEND_VECTOR_INREG into a vector shuffle with a zero vector
instead of (multiple) unpacks.
2. Improve SystemZ::GeneralShuffle to perform a single unpack as the last
operation if Bytes matches it.
Review: Ulrich Weigand
Differential Revision: https://reviews.llvm.org/D78486
