[clang] [Clang] Implement P2747 constexpr placement new (PR #104586)

[Aaron Ballman via cfe-commits]

================
@@ -10003,23 +10003,14 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
     return false;
 
   FunctionDecl *OperatorNew = E->getOperatorNew();
+  QualType AllocType = E->getAllocatedType();
+  QualType TargetType = AllocType;
 
   bool IsNothrow = false;
   bool IsPlacement = false;
-  if (OperatorNew->isReservedGlobalPlacementOperator() &&
-      Info.CurrentCall->isStdFunction() && !E->isArray()) {
-    // FIXME Support array placement new.
-    assert(E->getNumPlacementArgs() == 1);
-    if (!EvaluatePointer(E->getPlacementArg(0), Result, Info))
-      return false;
-    if (Result.Designator.Invalid)
-      return false;
-    IsPlacement = true;
-  } else if (!OperatorNew->isReplaceableGlobalAllocationFunction()) {
-    Info.FFDiag(E, diag::note_constexpr_new_non_replaceable)
-        << isa<CXXMethodDecl>(OperatorNew) << OperatorNew;
-    return false;
-  } else if (E->getNumPlacementArgs()) {
+
+  if (E->getNumPlacementArgs() && E->getNumPlacementArgs() == 1 &&
----------------
AaronBallman wrote:

```suggestion
  if (E->getNumPlacementArgs() == 1 &&
```
Unnecessary predicate.

https://github.com/llvm/llvm-project/pull/104586