[X86] Handle alls version of vXi1 insert_vector_elt with a constant index without falling back to shuffles.

We previously only supported inserting to the LSB or MSB where it was easy to zero to perform an OR to insert.

This change effectively extracts the old value and the new value, xors them together and then xors that single bit with the correct location in the original vector. This will cancel out the old value in the first xor leaving the new value in the position.

The way I've implemented this uses 3 shifts and two xors and uses an additional register. We can avoid the additional register at the cost of another shift.

llvm-svn: 320120

0 files changed, 0 insertions, 0 deletions