ComputeNumSignBits and computeKnownBits both trigger "Scalable flag
may be dropped" warnings when a fixed length vector is extracted
from a scalable vector. This patch assumes nothing about the
demanded elements thus matching the behaviour when extracting a
scalable vector from a scalable vector.
Differential Revision: https://reviews.llvm.org/D83642
We use extact_subvector and insert_subvector to "cast" between
fixed length and scalable vectors. This patch adds custom c++
based ISel for the following cases:
fixed_vector = ISD::EXTRACT_SUBVECTOR scalable_vector, 0
scalable_vector = ISD::INSERT_SUBVECTOR undef(scalable_vector), fixed_vector, 0
Which result in either EXTRACT_SUBREG/INSERT_SUBREG for NEON sized
vectors or COPY_TO_REGCLASS otherwise.
Differential Revision: https://reviews.llvm.org/D82871
Paul Walker