[llvm] [IndVars] Teach widenLoopCompare to use sext if narrow IV is positive and other operand is already sext. (PR #142703)

[Craig Topper via llvm-commits]

topperc wrote:

> As the narrow IV is always positive, can we use `zext nneg` instead?

We're extending the non-IV operand, we don't know about it's sign bit.

https://github.com/llvm/llvm-project/pull/142703