[llvm] [CodeGenPrepare] Fix signed overflow (PR #141487)

[Min-Yih Hsu via llvm-commits]

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

LGTM

> Thinking about this more I don't like the idea of adding a test that tests the debug print for something like this either. The only thing we gain is the coverage and nothing else. I still consider adding a test not worth it.

After revisiting this, I agree that we can probably leave it without a test for this particular case.

https://github.com/llvm/llvm-project/pull/141487