[gcc r16-982] c: fix ICE for mutually recursive structures [PR120381]

[Martin Uecker via Gcc-cvs]

https://gcc.gnu.org/g:0e0f963bcfbfce351dd4aad82e6dbc6fc84a0724

commit r16-982-g0e0f963bcfbfce351dd4aad82e6dbc6fc84a0724
Author: Martin Uecker <uec...@tugraz.at>
Date:   Thu May 29 19:13:46 2025 +0200

    c: fix ICE for mutually recursive structures [PR120381]
    
    For invalid nesting of a structure definition in a definition
    of itself or when using a rather obscure construction using statement
    expressions, we can create mutually recursive pairs of non-identical
    but compatible structure types.  This can lead to invalid composite
    types and an ICE.  If we detect recursion even for swapped pairs
    when forming composite types, this is avoided.
    
            PR c/120381
    
    gcc/c/ChangeLog:
            * c-typeck.cc (composite_type_internal): Stop recursion for
            swapped pairs.
    
    gcc/testsuite/ChangeLog:
            * gcc.dg/pr120381.c: New test.
            * gcc.dg/gnu23-tag-composite-6.c: New test.

Diff:
---
 gcc/c/c-typeck.cc                            |  2 +-
 gcc/testsuite/gcc.dg/gnu23-tag-composite-6.c | 11 +++++++++++
 gcc/testsuite/gcc.dg/pr120381.c              | 10 ++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 360216b96621..e5dd8d54c516 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -776,7 +776,7 @@ composite_type_internal (tree t1, tree t2, struct 
composite_cache* cache)
             construction, return it.  */
 
          for (struct composite_cache *c = cache; c != NULL; c = c->next)
-           if (c->t1 == t1 && c->t2 == t2)
+           if ((c->t1 == t1 && c->t2 == t2) || (c->t1 == t2 && c->t2 == t1))
               return c->composite;
 
          /* Otherwise, create a new type node and link it into the cache.  */
diff --git a/gcc/testsuite/gcc.dg/gnu23-tag-composite-6.c 
b/gcc/testsuite/gcc.dg/gnu23-tag-composite-6.c
new file mode 100644
index 000000000000..2411b04d3884
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gnu23-tag-composite-6.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-std=gnu23" } */
+
+int f()
+{
+    typedef struct foo bar;
+    struct foo { typeof(({ (struct foo { bar * x; }){ }; })) * x; } *q;
+    typeof(q->x) p;
+    1 ? p : q;
+}
+
diff --git a/gcc/testsuite/gcc.dg/pr120381.c b/gcc/testsuite/gcc.dg/pr120381.c
new file mode 100644
index 000000000000..5c017e60c6b2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr120381.c
@@ -0,0 +1,10 @@
+/* PR120381 */
+/* { dg-do compile } */
+
+struct A {
+  struct A {           /* { dg-error "nested redefinition" } */
+    struct A *p;
+  } *p;
+};
+int foo(const struct A *q) { return q->p == q; }
+