[llvm] [RISCV] Improve performCONCAT_VECTORCombine stride matching (PR #68726)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. Just leaving a note here that I think we'll fail to detect sequences of pointers that are a mixture of (base + index) and (add LastPtr, constStride), because the latter will be an SDValue and not a int64_t. But it sounds like an unlikely pattern to show up and I doubt its worth the complexity

https://github.com/llvm/llvm-project/pull/68726