[llvm] [Hexagon] Fix use-after-poison in balanceSubTree (PR #179239)

[Brian Cain via llvm-commits]

================
@@ -2194,11 +2224,21 @@ SDValue HexagonDAGToDAGISel::balanceSubTree(SDNode *N, bool TopLevel) {
       assert(ChildOpcode == NOpcode ||
              (NOpcode == ISD::MUL && ChildOpcode == ISD::SHL));
 
+      if (Child->getNumOperands() < 2) {
+        // Treat as a leaf if not enough operands
+        int Weight = getWeight(Child.getNode());
+        NodeHeights[Child] = getHeight(Child.getNode());
+        CurrentWeight += Weight;
+        Leaves.push(WeightedLeaf(Child, Weight, InsertionOrder++));
+        continue;
+      }
+
       // Convert SHL to MUL
       SDValue Op1;
-      if (ChildOpcode == ISD::SHL)
+      if (ChildOpcode == ISD::SHL) {
         Op1 = getMultiplierForSHL(Child.getNode());
-      else
+        assert(Op1.getNode() && "getMultiplierForSHL returned null");
----------------
androm3da wrote:

If `getMultiplierForSHL()` somehow returned null, the correct response is to alert someone to the logic error, not silently treat it as a leaf node.

https://github.com/llvm/llvm-project/pull/179239