[SVE][CodeGen] Add the isTruncatingStore flag to MSCATTER

[kmclaughlin]

Summary

This patch adds the IsTruncatingStore flag to MaskedScatterSDNode, set by getMaskedScatter().
Updated SelectionDAGDumper::print_details for MaskedScatterSDNode to print
the details of masked scatters (is truncating, signed or scaled).

This is the first in a series of patches which adds support for scalable masked scatters

[sdesmalen]

LGTM!

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

2444

nit: in the other functions like DAG.getMaskedScatter, IsTrunc is the last parameter after IndexType. Do you want to do that for the constructor as well for consistency?

[kmclaughlin]

• Made IsTrunc the last parameter to the MaskedScatterSDNode constructor
• Moved changes to SplitVecOp_MSCATTER, which split MemVT before creating the 'Hi' & 'Lo' scatters, into this patch from D90941

[sdesmalen]

Thanks for the changes @kmclaughlin, LGTM.