[llvm] [ValueTracking] Compute known FPClass from signbit idiom (PR #80740)

[Matt Arsenault via llvm-commits]

================
@@ -66,6 +66,10 @@ static void findAffectedValues(Value *Cond,
         // A > C3 && A < C4.
         if (match(A, m_Add(m_Value(X), m_ConstantInt())))
           AddAffected(X);
+        // Handle icmp slt/sgt (bitcast X to int), 0/-1
+        if (match(A, m_ElementWiseBitCast(m_Value(X))) &&
+            (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT))
----------------
arsenm wrote:

```suggestion
        if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SGT) &&
             match(A, m_ElementWiseBitCast(m_Value(X))))
```

https://github.com/llvm/llvm-project/pull/80740