[llvm] [InstCombine] Collect users iteratively (PR #131956)

[Matt Arsenault via llvm-commits]

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@@ -270,77 +270,87 @@ class PointerReplacer {
 } // end anonymous namespace
 
 bool PointerReplacer::collectUsers() {
-  if (!collectUsersRecursive(Root))
-    return false;
+  std::stack<User *> Worklist;
+  SmallSetVector<Instruction *, 4> ValuesToRevisit;
 
-  // Ensure that all outstanding (indirect) users of I
-  // are inserted into the Worklist. Return false
-  // otherwise.
-  return llvm::set_is_subset(ValuesToRevisit, Worklist);
-}
+  auto PushUsersToWorklist = [&](Instruction *Inst) {
+    for (auto *U : Inst->users())
+      if (isa<Instruction>(U) && !isAvailable(cast<Instruction>(U)))
+        Worklist.push(U);
+  };
 
-bool PointerReplacer::collectUsersRecursive(Instruction &I) {
-  for (auto *U : I.users()) {
-    auto *Inst = cast<Instruction>(&*U);
+  PushUsersToWorklist(&Root);
+  while (!Worklist.empty()) {
+    auto *Inst = dyn_cast<Instruction>(Worklist.top());
+    Worklist.pop();
+    if (!Inst)
+      return false;
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arsenm wrote:

With SmallVector you can use pop_back_val 

https://github.com/llvm/llvm-project/pull/131956