[llvm] [LoopUnroll] Enable allowexpensivetripcounts when user provides pragma (PR #181267)

[Adel Ejjeh via llvm-commits]

adelejjeh wrote:

@AaronBallman Since this change affects general loop unrolling behavior triggered by `#pragma unroll` across all targets, I'd like to get broader feedback before it goes in. Would you be able to loop in any appropriate Intel maintainers or stakeholders who might have opinions on how this interacts with Intel targets or use cases? I want to make sure this is well-reviewed from multiple target perspectives before merging.

https://github.com/llvm/llvm-project/pull/181267