[llvm] [llvm] Fix crash caused by reprocessing complex reductions (PR #122077)

[David Spickett via llvm-commits]

DavidSpickett wrote:

You can go ahead and land this once your reviewers are happy.

(and the obviously unrelated CI failure, I just saw a fix come by for that anyway)

https://github.com/llvm/llvm-project/pull/122077