[llvm] [LSR] Reuse identical casts and instructions across fixups (PR #201839)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

It looks like this PR contains multiple optimizations that should be able to stand on their own. It's reusing casts insts, reusing "rewritten insts" and simplifying with InstSimplify. Can you please split these into separate PRs? It's currently somewhat unclear what of the test impact comes from what change and whether everything has coverage.

https://github.com/llvm/llvm-project/pull/201839