[llvm] ConstraintElim: teach fact-transfer about samesign (PR #115893)

[Antonio Frighetto via llvm-commits]

================
@@ -1794,7 +1803,17 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
       if (ReproducerModule && DFSInStack.size() > ReproducerCondStack.size())
         ReproducerCondStack.emplace_back(Pred, A, B);
 
-      Info.transferToOtherSystem(Pred, A, B, CB.NumIn, CB.NumOut, DFSInStack);
+      if (ICmpInst::isRelational(Pred)) {
+        // If samesign is present on the ICmp, simply transfer the signed system
+        // to the unsigned system, and viceversa.
----------------
antoniofrighetto wrote:

```suggestion
        // If samesign is present on the ICmp, simply flip sign predicate and transfer such an information from the signed system
        // to the unsigned system, and viceversa.
```

https://github.com/llvm/llvm-project/pull/115893