[gcc r12-10299] Fortran: fix NULL pointer dereference on overlapping initialization [PR50410]

[Harald Anlauf]

https://gcc.gnu.org/g:cb72fbd49e1f0c1cbdf8a9e97860063b19b1f95e

commit r12-10299-gcb72fbd49e1f0c1cbdf8a9e97860063b19b1f95e
Author: Harald Anlauf <anlauf@gmx.de>
Date:   Thu Mar 28 22:34:40 2024 +0100

    Fortran: fix NULL pointer dereference on overlapping initialization [PR50410]
    
    gcc/fortran/ChangeLog:
    
            PR fortran/50410
            * trans-expr.cc (gfc_conv_structure): Check for NULL pointer.
    
    gcc/testsuite/ChangeLog:
    
            PR fortran/50410
            * gfortran.dg/data_initialized_4.f90: New test.
    
    (cherry picked from commit 6fb253a25dff13253d63553f02e0fe72c5e3ab4e)

Diff:
---
 gcc/fortran/trans-expr.cc                        |  2 +-
 gcc/testsuite/gfortran.dg/data_initialized_4.f90 | 16 ++++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/gcc/fortran/trans-expr.cc b/gcc/fortran/trans-expr.cc
index 27b34984705..11ee1931b8e 100644
--- a/gcc/fortran/trans-expr.cc
+++ b/gcc/fortran/trans-expr.cc
@@ -9298,7 +9298,7 @@ gfc_conv_structure (gfc_se * se, gfc_expr * expr, int init)
   cm = expr->ts.u.derived->components;
 
   for (c = gfc_constructor_first (expr->value.constructor);
-       c; c = gfc_constructor_next (c), cm = cm->next)
+       c && cm; c = gfc_constructor_next (c), cm = cm->next)
     {
       /* Skip absent members in default initializers and allocatable
 	 components.  Although the latter have a default initializer
diff --git a/gcc/testsuite/gfortran.dg/data_initialized_4.f90 b/gcc/testsuite/gfortran.dg/data_initialized_4.f90
new file mode 100644
index 00000000000..156b6607edf
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/data_initialized_4.f90
@@ -0,0 +1,16 @@
+! { dg-do compile }
+! { dg-additional-options "-std=legacy" }
+!
+! PR fortran/50410
+!
+! Silently allow overlapping initialization in legacy mode (used to ICE)
+
+program p
+  implicit none
+  type t
+     integer :: g = 1
+  end type t
+  type(t) :: u = t(2)
+  data u%g /3/
+  print *, u    ! this might print "2"
+end