[llvm] [LVI] Learn value ranges from ctpop/ctlz/cttz results (PR #121945)

[Yingwei Zheng via llvm-commits]

================
@@ -1159,6 +1162,49 @@ getRangeViaSLT(CmpInst::Predicate Pred, APInt RHS,
   return std::nullopt;
 }
 
+static bool matchBitIntrinsic(Value *LHS, Value *Val, Intrinsic::ID &IID) {
+  auto *II = dyn_cast<IntrinsicInst>(LHS);
+  if (!II)
+    return false;
+  auto ID = II->getIntrinsicID();
+  switch (ID) {
+  case Intrinsic::ctpop:
+  case Intrinsic::ctlz:
+  case Intrinsic::cttz:
+    break;
+  default:
+    return false;
+  }
+  if (II->getArgOperand(0) != Val)
+    return false;
+  IID = ID;
+  return true;
+}
+
+/// Get value range for a "ctpop(Val) Pred RHS" condition.
+ValueLatticeElement
+LazyValueInfoImpl::getValueFromICmpCtpop(ICmpInst::Predicate Pred, Value *RHS) {
+  unsigned BitWidth = RHS->getType()->getPrimitiveSizeInBits();
+
+  auto RHSConst = dyn_cast<ConstantInt>(RHS);
+  if (!RHSConst)
+    return ValueLatticeElement::getOverdefined();
+
+  auto &RHSVal = RHSConst->getValue();
+
+  ConstantRange ResValRange =
+      ConstantRange::makeAllowedICmpRegion(Pred, {RHSVal, RHSVal + 1});
----------------
dtcxzyw wrote:

```suggestion
      ConstantRange::makeExactICmpRegion(Pred, RHSVal);
```

https://github.com/llvm/llvm-project/pull/121945