[llvm] [IndVarSimplify] Add safety check for getTruncateExpr in genLoopLimit (PR #181296)

[Anshil Gandhi via llvm-commits]

gandhi56 wrote:

This is a reland of https://github.com/llvm/llvm-project/commit/4f551b55aeb316cd2d8f8f911908ea5bd4ced16b to eliminate orthogonal formatting changes.

https://github.com/llvm/llvm-project/pull/181296