[llvm] [Instcombine] Lower to explicit subtraction + unsigned comparison (PR #170896)

[Nikita Popov via llvm-commits]

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nikic wrote:

This code should not be inside foldIntrinsicWithOverflowCommon(), as this is not actually a common transform, it applies to only a single intrinsic.

https://github.com/llvm/llvm-project/pull/170896