[llvm] [clang] [InstCombine] Infer disjoint flag on Or instructions. (PR #72912)

[Craig Topper via cfe-commits]

topperc wrote:

Are the KnownBits in SimplifyDemandedBit usable? We have this code

```
    if (SimplifyDemandedBits(I, 1, DemandedMask, RHSKnown, Depth + 1) ||        
 
        SimplifyDemandedBits(I, 0, DemandedMask & ~RHSKnown.One, LHSKnown,      
 
                             Depth + 1)) { 
```

Can we trust the known bits for the LHS if we didn't demanded them due to known 
1s on the right hand side?

https://github.com/llvm/llvm-project/pull/72912
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