[llvm] [SCCP] Relax 2-insts range check to one-icmp check (PR #187997)

[Kunqiu Chen via llvm-commits]

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@@ -105,6 +105,112 @@ static ConstantRange getRange(Value *Op, SCCPSolver &Solver,
                                                        /*UndefAllowed=*/false);
 }
 
+/// SCCP already proves x \in KnownCR, so only ActiveCmpCR = CmpCR ∩ KnownCR
+/// matters. Try to replace CmpCR with a simpler equivalent range NewCmpCR
+/// such that NewCmpCR ∩ KnownCR == ActiveCmpCR.
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Camsyn wrote:

In fact, simplifying `CmpCR ∩ KnownCR` is equivalent to simplifying `CmpCR.inverse() ∩ KnownCR`.
Let `R = CmpCR ∩ KnownCR, R' = CmpCR.inverse() ∩ KnownCR`, we have $R = \text{CmpCR} \setminus R'$.

And I cannot find any case where $R'$ can be simplified while $R$ cannot.

https://github.com/llvm/llvm-project/pull/187997