[CodeGen] Fix handling of nullptr in initializers

Fixes #137276.

Author: alexfh

clang/lib/CodeGen/CodeGenTypes.cpp

@@ -850,12 +850,14 @@ CodeGenTypes::getCGRecordLayout(const RecordDecl *RD) {
 }
 
 bool CodeGenTypes::isPointerZeroInitializable(QualType T) {
-  assert((T->isAnyPointerType() || T->isBlockPointerType()) && "Invalid type");
+  assert((T->isAnyPointerType() || T->isBlockPointerType() ||
+          T->isNullPtrType()) &&
+         "Invalid type");
   return isZeroInitializable(T);
 }
 
 bool CodeGenTypes::isZeroInitializable(QualType T) {
-  if (T->getAs<PointerType>())
+  if (T->getAs<PointerType>() || T->isNullPtrType())
     return Context.getTargetNullPointerValue(T) == 0;
 
   if (const auto *AT = Context.getAsArrayType(T)) {

clang/test/CodeGenCXX/pr137276.cpp

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
+using ulong = unsigned long;
+template <class... Ts>
+void g(Ts... args) {
+  ulong arr[3] = {ulong(args)...};
+  (void)arr;
+}
+extern void f() {
+  g(nullptr, 17);
+}
+
+// CHECK: {{^}}  store i64 0, ptr %arr, align 8{{$}}