[llvm] [InstCombine] Combine trunc (lshr X, BW-1) to i1 --> icmp slt X, 0 (#142593) (PR #143846)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

I've merged against trunk to kick off another CI build - it doesn't look like the patch is responsible for the fail but let's see if we can confirm

https://github.com/llvm/llvm-project/pull/143846