[llvm] [flang] Clear obsolete type from reallocated allocatable (PR #139788)

[Peter Klausler via llvm-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/139788

When an assignment to a polymorphic allocatable changes its type to an intrinsic type, be sure to reset its descriptor's derived type pointer to null.

Fixes https://github.com/llvm/llvm-project/issues/136522.

>From a302027daae3d380958046453c306c90be4fb283 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Tue, 13 May 2025 13:15:57 -0700
Subject: [PATCH] [flang] Clear obsolete type from reallocated allocatable

When an assignment to a polymorphic allocatable changes its
type to an intrinsic type, be sure to reset its descriptor's
derived type pointer to null.

Fixes https://github.com/llvm/llvm-project/issues/136522.
---
 flang-rt/lib/runtime/assign.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/flang-rt/lib/runtime/assign.cpp b/flang-rt/lib/runtime/assign.cpp
index 4a813cd489022..9be75da9520e3 100644
--- a/flang-rt/lib/runtime/assign.cpp
+++ b/flang-rt/lib/runtime/assign.cpp
@@ -79,15 +79,18 @@ static RT_API_ATTRS int AllocateAssignmentLHS(
     to.raw().elem_len = from.ElementBytes();
   }
   const typeInfo::DerivedType *derived{nullptr};
+  DescriptorAddendum *toAddendum{to.Addendum()};
   if (const DescriptorAddendum * fromAddendum{from.Addendum()}) {
     derived = fromAddendum->derivedType();
-    if (DescriptorAddendum * toAddendum{to.Addendum()}) {
+    if (toAddendum) {
       toAddendum->set_derivedType(derived);
       std::size_t lenParms{derived ? derived->LenParameters() : 0};
       for (std::size_t j{0}; j < lenParms; ++j) {
         toAddendum->SetLenParameterValue(j, fromAddendum->LenParameterValue(j));
       }
     }
+  } else if (toAddendum) {
+    toAddendum->set_derivedType(nullptr);
   }
   // subtle: leave bounds in place when "from" is scalar (10.2.1.3(3))
   int rank{from.rank()};