[llvm] [InstCombine] Simplify zext(sub(0, trunc(x))) -> and(sub(0, x), mask) (Fixes #165306) (PR #167101)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

IIRC i6 was used just to stop alive2 from timing out 

https://github.com/llvm/llvm-project/pull/167101