This is a workaround for another issue related to PR118765.
I do not yet understand what goes wrong in merge_decls in
this case (somehow we end up with TYPE_DECLS where
DECL_ORIGINAL_TYPE is not set correctly, so we can not
determine the correct tag later), so I do not merge
these TYPE_DECLS in this specific case as a workaround
and add a "sorry" for the alignment case (or should this
simply become an error?).
Bootstrapped and regression tested on x86_64.
commit 56c2c96ef4ebd24290fbf8f66b277d420a68b032
Author: Martin Uecker <uec...@tugraz.at>
Date: Sun Mar 16 10:54:17 2025 +0100
c: Fix tagname confusion for typedef redefinitions [PR118765]
When we redefine a typedef for a tagged type that has just been
redefined, merge_decls may produce invalid TYPE_DECLS that are not
consistent with what set_underlying_type produces. Do not call
merge_decls in this specific case for now and instead return the
new declaration. If the user used inconsistent alignment for
different typedef declarations, emit a sorry message.
PR c/118765
gcc/ChangeLog:
* c/c-decl.cc (diagnose_mismatched_decls): Return false
for typedef redefinitions of redefined tagged types.
* c/c-typeck.cc (tagged_types_tu_compatible_p): Add
checking assertions.
gcc/testsuite/ChangeLog:
* gcc.dg/pr118765-2.c: New test.
* gcc.dg/typedef-redecl3.c: New test.
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 1ae520828c3..58b1c41b961 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -2360,6 +2360,21 @@ diagnose_mismatched_decls (tree newdecl, tree olddecl,
"redefinition of typedef %q+D", newdecl))
locate_old_decl (olddecl);
+ /* FIXME: merge_decls produces incorrect TYPE_DECLS for redefinitions
+ that involve defined tagged types. Use the new declaration for now. */
+ if (TYPE_MAIN_VARIANT (newtype) != TYPE_MAIN_VARIANT (oldtype)
+ && flag_isoc23
+ && (RECORD_OR_UNION_TYPE_P (newtype)
+ || ENUMERAL_TYPE == TREE_CODE (newtype)))
+ {
+ if (TYPE_ALIGN (newtype) != TYPE_ALIGN (oldtype))
+ {
+ sorry ("redefinition of typedef %q+D with different alignment "
+ "is not supported for redefined tagged types", newdecl);
+ locate_old_decl (olddecl);
+ }
+ return false;
+ }
return true;
}
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 1a39cbb2009..c91b7dddae8 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1812,6 +1812,10 @@ tagged_types_tu_compatible_p (const_tree t1, const_tree
t2,
to go look at the original type. */
t1 = c_type_original (t1);
t2 = c_type_original (t2);
+ gcc_checking_assert (!TYPE_NAME (t1)
+ || TREE_CODE (TYPE_NAME (t1)) == IDENTIFIER_NODE);
+ gcc_checking_assert (!TYPE_NAME (t2)
+ || TREE_CODE (TYPE_NAME (t2)) == IDENTIFIER_NODE);
if (TYPE_NAME (t1) != TYPE_NAME (t2))
return false;
diff --git a/gcc/testsuite/gcc.dg/pr118765-2.c
b/gcc/testsuite/gcc.dg/pr118765-2.c
new file mode 100644
index 00000000000..0c3e4988118
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118765-2.c
@@ -0,0 +1,33 @@
+/* { dg-do "compile" } */
+/* { dg-options "-std=gnu23" } */
+
+typedef struct q { int x; } q_t;
+typedef struct q { int x; } q_t;
+typedef struct q { int x; } q_t;
+typedef struct q { int x; } q_t;
+typedef struct q { int x; } q_t;
+
+typedef struct r r_t;
+typedef struct r r_t;
+typedef struct r r_t;
+typedef struct r r_t;
+typedef struct r r_t;
+
+extern struct s { int x; } s;
+extern struct s { int x; } s;
+extern struct s { int x; } s;
+extern struct s { int x; } s;
+extern struct s { int x; } s;
+
+struct t { int x; };
+struct t { int x; };
+struct t { int x; };
+struct t { int x; };
+struct t { int x; };
+
+typedef enum e { E = 1 } e_t;
+typedef enum e { E = 1 } e_t;
+typedef enum e { E = 1 } e_t;
+typedef enum e { E = 1 } e_t;
+typedef enum e { E = 1 } e_t;
+
diff --git a/gcc/testsuite/gcc.dg/typedef-redecl3.c
b/gcc/testsuite/gcc.dg/typedef-redecl3.c
new file mode 100644
index 00000000000..a2424d6b7ab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/typedef-redecl3.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+#define N 64
+
+struct f { int x; };
+typedef struct f T;
+typedef struct f T __attribute__((aligned (N)));
+typedef struct f T __attribute__((aligned (N * 2)));
+typedef struct f T __attribute__((aligned (N)));
+typedef struct f T;
+
+_Static_assert (_Alignof (T) == N * 2, "N * 2");
+
+enum g { A = 1 };
+typedef enum g S;
+typedef enum g S __attribute__((aligned (N)));
+typedef enum g S __attribute__((aligned (N * 2)));
+typedef enum g S __attribute__((aligned (N)));
+typedef enum g S;
+
+_Static_assert (_Alignof (S) == N * 2, "N * 2");
+
