[llvm] [IR] Add disjoint flag for Or instructions. (PR #72583)

[Matt Arsenault via llvm-commits]

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@@ -10012,6 +10013,12 @@ The truth table used for the '``or``' instruction is:
 |   1 |   1 |   1 |
 +-----+-----+-----+
 
+``disjoint`` means every bit is known to be zero in at least one of the inputs.
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arsenm wrote:

My reading of "every bit" seems a bit ambiguous. I thought the point was that comparing each individual bit, each must be 0. But this reads to me more like one of the values as a whole is 0 

https://github.com/llvm/llvm-project/pull/72583