The first attempt was reverted because a clang test changed
unexpectedly - the file is already marked with a FIXME, so
I just updated it this time to pass.
Original commit message:
This is the main patch for converting a truncated scalar that is
inserted into a vector to bitcast+shuffle. We could go either way
on patterns like this, but this direction will allow collapsing a
pair of these sequences on the motivating example from issue
The patch is split into 3 parts to make it easier to see the
progression of tests diffs. We allow inserting/shuffling into a
different size vector for flexibility, so there are several test
variations. The length-changing is handled by shortening/padding
the shuffle mask with undef elements.
In part 1, handle the basic pattern:
inselt undef, (trunc T), IndexC --> shuffle (bitcast T), IdentityMask
Proof for the endian-dependency behaving as expected:
https://alive2.llvm.org/ce/z/BsA7yC
The TODO items for handling shifts and insert into an arbitrary base
vector value are implemented as follow-ups.
Differential Revision: https://reviews.llvm.org/D138872
e71b81cab0