[clang] [libcxx] [clang] Add builtin to clear padding bytes (prework for P0528R3) (PR #75371)

[Eli Friedman via cfe-commits]

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@@ -2538,6 +2541,311 @@ static RValue EmitHipStdParUnsupportedBuiltin(CodeGenFunction *CGF,
   return RValue::get(CGF->Builder.CreateCall(UBF, Args));
 }
 
+namespace {
+
+struct PaddingClearer {
+  PaddingClearer(CodeGenFunction &F)
+      : CGF(F), CharWidth(CGF.getContext().getCharWidth()) {}
+
+  void run(Value *Ptr, QualType Ty) {
+    OccuppiedIntervals.clear();
+    Queue.clear();
+
+    Queue.push_back(Data{0, Ty, true});
+    while (!Queue.empty()) {
+      auto Current = Queue.front();
+      Queue.pop_front();
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efriedma-quic wrote:

Can you just use back()/pop_back() here (so you don't need an std::deque)?

https://github.com/llvm/llvm-project/pull/75371