[llvm] [DAG] ComputeNumSignBits - ISD::EXTRACT_ELEMENT needs to return at least 1 (PR #155455)

[Miguel Saldivar via llvm-commits]

Saldivarcher wrote:

> Description and/or title should mention the affected opcode.

Thanks for the tip, I didn't know that! Let me know how that looks now. 

https://github.com/llvm/llvm-project/pull/155455