This adds Post inc variants of the VLD2/4 and VST2/4 instructions in MVE. It uses the same mechanism/nodes as Neon, transforming the intrinsic+add pair into a ARMISD::VLD2_UPD, which gets selected to a post-inc instruction. The code to do that is mostly taken from the existing Neon code, but simplified as less variants are needed.
It also fills in some getTgtMemIntrinsic for the arm.mve.vld2/4 instrinsics, which allow the nodes to have MMO's, calculated as the full length to the memory being loaded/stored.
If I understand this part right, it's trying to arrange that the IR intrinsics for vld2/vst2 are turned into something that can be writeback-optimized. But there don't seem to be many tests of that part – I saw one test that had a vld2q intrinsic call, but no tests of vld4, or stores.