[clang] [LifetimeSafety] Add placement new support (PR #194030)

[Utkarsh Saxena via cfe-commits]

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@@ -626,9 +632,31 @@ void FactsGenerator::VisitArraySubscriptExpr(const ArraySubscriptExpr *ASE) {
 void FactsGenerator::VisitCXXNewExpr(const CXXNewExpr *NE) {
   OriginList *NewList = getOriginsList(*NE);
 
-  const Loan *L = createLoan(FactMgr, NE);
-  CurrentBlockFacts.push_back(
-      FactMgr.createFact<IssueFact>(L->getID(), NewList->getOuterOriginID()));
+  // Check if we have a placement new where the second argument is void*, to
+  // avoid flowing from non-pointer parameters, such as std::nothrow.
+  // And that the placement parameter num is 1,
+  // that is to mostly limit to standard library placement new.
+  if (NE->getNumPlacementArgs() == 1) {
+    if (const auto *Arg = NE->getOperatorNew()
+                              ->getParamDecl(1)
+                              ->getType()
+                              ->getAs<PointerType>();
+        Arg && Arg->isVoidPointerType()) {
+      const Expr *PlacementArg = NE->getPlacementArg(0)->IgnoreImpCasts();
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usx95 wrote:

I am not a big fan of making this work without a general solution of writing to aliases of origins. (e.g. `placement_new_member_call_from_dead_scope`)

Let's keep it simple for now and flow from PlacementList to NewList

(See another thread which talks about an alias analysis required to solve this)

https://github.com/llvm/llvm-project/pull/194030