[llvm] [InstCombine] Simplify phi using KnownBits of condition (PR #134712)

[Andreas Jonson via llvm-commits]

andjo403 wrote:

> Compile-time overhead: +~0.2%

The compile time looks mush better now even an overall improvement 
Compile-time overhead: -~0.02%

https://github.com/llvm/llvm-project/pull/134712