The existing code was not updating the uses of loads that it recreated,
leading to incorrect chains which could break the ordering between
nodes. This moves the code to a combine instead, and makes sure we
update the chain references. This does mean it happens earlier -
potentially before the concats are simplified. This can lead to
inefficiencies in the codegen, which will be fixed in followups.
We already have custom lowering for v4i8 load, which loads as a f32,
converts to a vector and bitcasts and extends the result to a v4i16.
This adds some custom lowering of concat(v4i8 load, ...) to keep the
result as an f32 and create a buildvector of the resulting f32 loads.
This helps not create all the extends and bitcasts, which are often
difficult to fully clean up.
Differential Revision: https://reviews.llvm.org/D121400
This turns upz1(x, undef) to concat(truncate(x), undef), as the truncate
is simpler and can often be optimized away, and it helps some of the
insert-subvector tests optimize more cleanly.
Differential Revision: https://reviews.llvm.org/D120879
