[llvm] [SLP]Cancel scheduling of the trimmed nodes (PR #226268)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> I'm seeing a 5% slowdown on SPEC2026 LBM from this: [repro.ll.txt](https://github.com/user-attachments/files/32754064/repro.ll.txt)

Hope it is fixed by c8ae6e04d629ee08b74248155143698e0e31e6d5, though, actually, it is mostly the instructions scheduling (codegen issue), not SLP. But this patch itself also tries to help codegen.

https://github.com/llvm/llvm-project/pull/226268