[NFC] Switched to StackList.

No need for a worklist of any sort, a simple list suffices.

Author: nate-chandler

lib/SILOptimizer/Transforms/CopyPropagation.cpp

@@ -419,15 +419,15 @@ void CopyPropagation::run() {
   InstructionDeleter deleter(std::move(callbacks));
   bool changed = false;
 
-  GraphNodeWorklist<BeginBorrowInst *, 16> beginBorrowsToShrink;
+  StackList<BeginBorrowInst *> beginBorrowsToShrink(f);
 
   // Driver: Find all copied or borrowed defs.
   for (auto &bb : *f) {
     for (auto &i : bb) {
       if (auto *copy = dyn_cast<CopyValueInst>(&i)) {
         defWorklist.updateForCopy(copy);
       } else if (auto *borrow = dyn_cast<BeginBorrowInst>(&i)) {
-        beginBorrowsToShrink.insert(borrow);
+        beginBorrowsToShrink.push_back(borrow);
       } else if (canonicalizeAll) {
         if (auto *destroy = dyn_cast<DestroyValueInst>(&i)) {
           defWorklist.updateForCopy(destroy->getOperand());
@@ -446,7 +446,7 @@ void CopyPropagation::run() {
   // NOTE: We assume that the function is in reverse post order so visiting the
   //       blocks and pushing begin_borrows as we see them and then popping them
   //       off the end will result in shrinking inner borrow scopes first.
-  while (auto *bbi = beginBorrowsToShrink.pop()) {
+  for (auto *bbi : beginBorrowsToShrink) {
     bool firstRun = true;
     // Run the sequence of utilities:
     // - ShrinkBorrowScope