[gcc r16-6321] fortran: [PR121472] Fix ICE with constructor for finalized zero-size type.

[Jerry DeLisle]

https://gcc.gnu.org/g:5bb465a789600a46f3b53b236ba07b30cea6cbac

commit r16-6321-g5bb465a789600a46f3b53b236ba07b30cea6cbac
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Sun Dec 21 13:33:15 2025 -0800

    fortran: [PR121472] Fix ICE with constructor for finalized zero-size type.
    
    When a derived type has a final subroutine and a constructor interface,
    but is effectively zero-sized, the gimplifier fails on the finalization
    code.  The existing check for empty types (!derived->components) only
    catches completely empty types, not types with empty components.
    Replace with a tree-level TYPE_SIZE_UNIT check that catches all
    zero-size cases.
    
            PR fortran/121472
    
    gcc/fortran/ChangeLog:
    
            * trans.cc (gfc_finalize_tree_expr): Replace !derived->components
            check with TYPE_SIZE_UNIT check for zero-size types.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/pr121472.f90: New test.

Diff:
---
 gcc/fortran/trans.cc                   |  9 ++++++---
 gcc/testsuite/gfortran.dg/pr121472.f90 | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/gcc/fortran/trans.cc b/gcc/fortran/trans.cc
index dcacf94e4130..18d2f1289feb 100644
--- a/gcc/fortran/trans.cc
+++ b/gcc/fortran/trans.cc
@@ -1641,12 +1641,15 @@ gfc_finalize_tree_expr (gfc_se *se, gfc_symbol *derived,
     }
   else if (derived && gfc_is_finalizable (derived, NULL))
     {
-      if (!derived->components && (!rank || attr.elemental))
+      tree type = TREE_TYPE (se->expr);
+      if (type && TYPE_SIZE_UNIT (type)
+	  && integer_zerop (TYPE_SIZE_UNIT (type))
+	  && (!rank || attr.elemental))
 	{
 	  /* Any attempt to assign zero length entities, causes the gimplifier
 	     all manner of problems. Instead, a variable is created to act as
-	     as the argument for the final call.  */
-	  desc = gfc_create_var (TREE_TYPE (se->expr), "zero");
+	     the argument for the final call.  */
+	  desc = gfc_create_var (type, "zero");
 	}
       else if (se->direct_byref)
 	{
diff --git a/gcc/testsuite/gfortran.dg/pr121472.f90 b/gcc/testsuite/gfortran.dg/pr121472.f90
new file mode 100644
index 000000000000..00c990cd267e
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr121472.f90
@@ -0,0 +1,33 @@
+! { dg-do compile }
+! PR fortran/121472 - ICE with constructor for finalized zero-size type
+
+module pr121472_m
+    implicit none
+    type r
+    end type
+
+    type ip
+        type(r) :: r_member
+    contains
+        final :: ipd
+    end type
+
+    interface ip
+        module procedure ipc
+    end interface
+contains
+    subroutine ipd(this)
+        type(ip), intent(inout) :: this
+    end subroutine
+
+    function ipc() result(res)
+        type(ip) :: res
+    end function
+end module
+
+program test
+    use pr121472_m
+    implicit none
+    type(ip) :: p
+    p = ip()
+end program