Found by inspecting AMDGPU assembly - so the arithmetic ops created
there were definitely making their way into the target ISA. A
`LLVM::BitcastOp` seems equivalent, and evaporates as expected in the
target asm.
Along the way, I thought that this helper function `mfmaConcatIfNeeded`
could be renamed to `convertMFMAVectorOperand` to better convey its
contract; so I don't need to think about whether a bitcast is a
legitimate "concat" :-)
---------
Signed-off-by: Benoit Jacob <jacob.benoit.1@gmail.com>
d8a656ffaf