[llvm] [SandboxVec][DAG] Implement UnscheduledSuccs (PR #112255)

[Sriraman Tallam via llvm-commits]

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@@ -215,8 +224,15 @@ class MemDGNode final : public DGNode {
   MemDGNode *getPrevNode() const { return PrevMemN; }
   /// \Returns the next Mem DGNode in instruction order.
   MemDGNode *getNextNode() const { return NextMemN; }
-  /// Adds the mem dependency edge PredN->this.
-  void addMemPred(MemDGNode *PredN) { MemPreds.insert(PredN); }
+  /// Adds the mem dependency edge PredN->this. This also increments the
+  /// UnscheduledSuccs counter of the predecessor if this node has not been
+  /// scheduled.
+  void addMemPred(MemDGNode *PredN) {
+    MemPreds.insert(PredN);
+    if (!Scheduled) {
+      ++PredN->UnscheduledSuccs;
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tmsri wrote:

What if PredN already exists in MemPreds?

https://github.com/llvm/llvm-project/pull/112255