From: Martin Uecker <uecker@tugraz.at>
Date: Sat, 1 Mar 2025 20:32:21 +0000 (+0100)
Subject: c: Fix bug in typedef redefinitions of tagged types [PR118765]
X-Git-Tag: basepoints/gcc-16~1266
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1636e85270d918a84d57bb521c22c42abf42a47c;p=thirdparty%2Fgcc.git

c: Fix bug in typedef redefinitions of tagged types [PR118765]

When we redefine a tagged type we incorrectly update TYPE_STUB_DECL
of the previously defined type instead of the new one.  Because
TYPE_STUB_DECL is used when determining whether two such types are
the same, this can cause valid typedef redefinitions to be rejected
later. This is only a partial fix for PR118765.

	PR c/118765

gcc/c/ChangeLog:
	* c-decl.cc (finish_struct,finish_enum): Swap direction when
	copying TYPE_STRUB_DECL in redefinitions.

gcc/testsuite/ChangeLog:
	* gcc.dg/pr118765.c: New test.
---

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 0dcbae9b26f..1ae520828c3 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -9846,7 +9846,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
 	  && TREE_CODE (vistype) == TREE_CODE (t)
 	  && !C_TYPE_BEING_DEFINED (vistype))
 	{
-	  TYPE_STUB_DECL (vistype) = TYPE_STUB_DECL (t);
+	  TYPE_STUB_DECL (t) = TYPE_STUB_DECL (vistype);
 	  if (c_type_variably_modified_p (t))
 	    {
 	      error ("redefinition of struct or union %qT with variably "
@@ -10321,7 +10321,7 @@ finish_enum (tree enumtype, tree values, tree attributes)
 	  && TREE_CODE (vistype) == TREE_CODE (enumtype)
 	  && !C_TYPE_BEING_DEFINED (vistype))
 	{
-	  TYPE_STUB_DECL (vistype) = TYPE_STUB_DECL (enumtype);
+	  TYPE_STUB_DECL (enumtype) = TYPE_STUB_DECL (vistype);
 	  if (!comptypes_same_p (enumtype, vistype))
 	    error("conflicting redefinition of enum %qT", enumtype);
 	}
diff --git a/gcc/testsuite/gcc.dg/pr118765.c b/gcc/testsuite/gcc.dg/pr118765.c
new file mode 100644
index 00000000000..12d025979e3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118765.c
@@ -0,0 +1,7 @@
+/* { dg-do "compile" } */
+/* { dg-options "-std=gnu23" } */
+
+typedef struct q { int x; } q_t;
+struct q { int x; };
+typedef struct q { int x; } q_t;
+