[gcc r14-10761] c: fix crash when checking for compatibility of structures [PR116726]

[Martin Uecker via Gcc-cvs]

https://gcc.gnu.org/g:4123f546d77c42287d2fcae6fb04df7b87193454

commit r14-10761-g4123f546d77c42287d2fcae6fb04df7b87193454
Author: Martin Uecker <uec...@tugraz.at>
Date:   Tue Sep 17 11:37:29 2024 +0200

    c: fix crash when checking for compatibility of structures [PR116726]
    
    When checking for compatibility of structure or union types in
    tagged_types_tu_compatible_p, restore the old value of the pointer to
    the top of the temporary cache after recursively calling comptypes_internal
    when looping over the members of a structure of union.  While the next
    iteration of the loop overwrites the pointer, I missed the fact that it can
    be accessed again when types of function arguments are compared as part
    of recursive type checking and the function is entered again.
    
            PR c/116726
    
    gcc/c/ChangeLog:
    
            * c-typeck.cc (tagged_types_tu_compatible_p): Restore value
            of the cache after recursing into comptypes_internal.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/pr116726.c: New test.
    
    (cherry picked from commit 9227a64495d5594613604573b72422e8e3722fc5)

Diff:
---
 gcc/c/c-typeck.cc               |  5 ++++-
 gcc/testsuite/gcc.dg/pr116726.c | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 4567b114734b..ebc2c288f981 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1611,8 +1611,11 @@ tagged_types_tu_compatible_p (const_tree t1, const_tree 
t2,
 
            data->anon_field = !DECL_NAME (s1);
 
+           const struct tagged_tu_seen_cache *cache = data->cache;
            data->cache = &entry;
-           if (!comptypes_internal (TREE_TYPE (s1), TREE_TYPE (s2), data))
+           bool ret = comptypes_internal (TREE_TYPE (s1), TREE_TYPE (s2), 
data);
+           data->cache = cache;
+           if (!ret)
              return false;
 
            tree st1 = TYPE_SIZE (TREE_TYPE (s1));
diff --git a/gcc/testsuite/gcc.dg/pr116726.c b/gcc/testsuite/gcc.dg/pr116726.c
new file mode 100644
index 000000000000..bb25efca5864
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr116726.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c23" } */
+
+struct s1 {
+  int f1;
+};
+struct s2 {
+  int f2;
+};
+struct s1 f(struct s2 *);
+
+struct s1 {
+  int f1;
+};
+struct s2 {
+  int f2;
+};
+struct s1 f(struct s2 *);