[PATCH] c: Fix ICE for redeclaration of structs with different alignment [PR114727]

[Martin Uecker]

This fixes an ICE when redeclaring a struct and having
an aligned attribute in one version in C23.


Bootstrapped and regression tested on x86_64.



    c: Fix ICE for redeclaration of structs with different alignment [PR114727]
    
    For redeclarations of struct in C23, if one has an alignment attribute
    that makes the alignment different, we later get an ICE in verify_types.
    This patches disallows such redeclarations by declaring such types to
    be different.
    
            PR c/114727
    
    gcc/c/
            * c-typeck.cc (tagged_types_tu_compatible): Add test.
    
    gcc/testsuite/
            * gcc.dg/pr114727.c: New test.

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index e486ac04f9c..455dc374b48 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1603,6 +1603,9 @@ tagged_types_tu_compatible_p (const_tree t1, const_tree 
t2,
          != TYPE_REVERSE_STORAGE_ORDER (t2)))
     return false;
 
+  if (TYPE_USER_ALIGN (t1) != TYPE_USER_ALIGN (t2))
+    data->different_types_p = true;
+
   /* For types already being looked at in some active
      invocation of this function, assume compatibility.
      The cache is built as a linked list on the stack
diff --git a/gcc/testsuite/gcc.dg/pr114727.c b/gcc/testsuite/gcc.dg/pr114727.c
new file mode 100644
index 00000000000..12949590ce0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr114727.c
@@ -0,0 +1,6 @@
+/* { dg-do compile }
+ * { dg-options "-std=c23 -g" } */
+
+#define Y [[gnu::aligned(128)]]
+extern struct Y foo { int x; } x;
+struct foo { int x; };         /* { dg-error "redefinition" } */