[llvm] [LoadStoreVectorizer] Fill gaps in load/store chains to enable vectorization (PR #159388)

[Drew Kersnar via llvm-commits]

dakersnar wrote:

Added a test that combines redundant loads with gap filling and chain extending. I'm also going to _temporarily_ push a cherry pick of https://github.com/llvm/llvm-project/pull/159387 into this branch to ensure the pipeline is green, and then I'll rebase it away to make reviewing easier again. Just looking for showstoppers. If anyone happens to review this change while that is happening, ignore the changes from that commit.

https://github.com/llvm/llvm-project/pull/159388