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

[Yingwei Zheng via llvm-commits]

================
@@ -1812,6 +1813,61 @@ 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(Cmp0->getPredicate(), *C0);
+  auto Range1 = ConstantFPRange::makeExactFCmpRegion(Cmp1->getPredicate(), *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 (IsAnd && (*Range0).intersectWith(*Range1).isEmptySet())
+    return getFalse(Cmp0->getType());
+
+  // For or-of-compares, check if the union is full:
+  // (fcmp X, C0) || (fcmp X, C1) --> full set --> true
+  //
+  // TODO: `unionWith` is not precise at the moment, so
+  // we can invert the predicate and check:
+  // inv(fcmp X, C0) && inv(fcmp X, C1) --> empty set --> false
+  if (!IsAnd) {
+    auto Range0Inv = ConstantFPRange::makeExactFCmpRegion(
+        FCmpInst::getInversePredicate(Cmp0->getPredicate()), *C0);
+    auto Range1Inv = ConstantFPRange::makeExactFCmpRegion(
+        FCmpInst::getInversePredicate(Cmp1->getPredicate()), *C1);
+    if (Range0Inv && Range1Inv) {
+      if ((*Range0Inv).intersectWith(*Range1Inv).isEmptySet())
+        return getFalse(Cmp0->getType());
+    }
+  }
----------------
dtcxzyw wrote:

```suggestion
```
Handled by the logic above.

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