[llvm] [InstCombine] Generalise optimisation of redundant floating point comparisons with `ConstantFPRange` (PR #159315)

[Yingwei Zheng via llvm-commits]

================
@@ -1812,6 +1813,46 @@ static Value *simplifyOrOfICmps(ICmpInst *Op0, ICmpInst *Op1,
   return nullptr;
 }
 
+/// Test if a pair of compares with a shared operand and 2 constants has an
+/// empty set intersection, full set union, or if one compare is a superset of
+/// the other.
+static Value *simplifyAndOrOfFCmpsWithConstants(FCmpInst *Cmp0, FCmpInst *Cmp1,
+                                                bool IsAnd) {
+  // Look for this pattern: {and/or} (fcmp X, C0), (fcmp X, C1)).
+  if (Cmp0->getOperand(0) != Cmp1->getOperand(0))
+    return nullptr;
+
+  const APFloat *C0, *C1;
+  if (!match(Cmp0->getOperand(1), m_APFloat(C0)) ||
+      !match(Cmp1->getOperand(1), m_APFloat(C1)))
+    return nullptr;
+
+  auto Range0 = ConstantFPRange::makeExactFCmpRegion(
+      IsAnd ? Cmp0->getPredicate() : Cmp0->getInversePredicate(), *C0);
+  auto Range1 = ConstantFPRange::makeExactFCmpRegion(
+      IsAnd ? Cmp1->getPredicate() : Cmp1->getInversePredicate(), *C1);
+
+  if (!Range0 || !Range1)
+    return nullptr;
+
+  // For and-of-compares, check if the intersection is empty:
+  // (fcmp X, C0) && (fcmp X, C1) --> empty set --> false
+  if ((*Range0).intersectWith(*Range1).isEmptySet())
----------------
dtcxzyw wrote:

```suggestion
  if (Range0->intersectWith(*Range1).isEmptySet())
```

https://github.com/llvm/llvm-project/pull/159315