[gcc r12-4032] c++: Fix handling of __thread/thread_local extern vars declared at function scope [PR102496]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:701075864ac4d1c6cec936d10f9cfc2aeb8c1699

commit r12-4032-g701075864ac4d1c6cec936d10f9cfc2aeb8c1699
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Oct 1 10:30:16 2021 +0200

    c++: Fix handling of __thread/thread_local extern vars declared at function scope [PR102496]
    
    The introduction of push_local_extern_decl_alias in
    r11-3699-g4e62aca0e0520e4ed2532f2d8153581190621c1a
    broke tls vars, while the decl they are created for has the tls model
    set properly, nothing sets it for the alias that is actually used,
    so accesses to it are done as if they were normal variables.
    This is then diagnosed at link time if the definition of the extern
    vars is __thread/thread_local.
    
    2021-10-01  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/102496
            * name-lookup.c (push_local_extern_decl_alias): Return early even for
            tls vars with non-dependent type when processing_template_decl.  For
            CP_DECL_THREAD_LOCAL_P vars call set_decl_tls_model on alias.
    
            * g++.dg/tls/pr102496-1.C: New test.
            * g++.dg/tls/pr102496-2.C: New test.

Diff:
---
 gcc/cp/name-lookup.c                  |  7 ++++++-
 gcc/testsuite/g++.dg/tls/pr102496-1.C | 20 ++++++++++++++++++++
 gcc/testsuite/g++.dg/tls/pr102496-2.C |  6 ++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index ddee8b390f9..c414a1091b4 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -3375,7 +3375,10 @@ set_decl_context_in_fn (tree ctx, tree decl)
 void
 push_local_extern_decl_alias (tree decl)
 {
-  if (dependent_type_p (TREE_TYPE (decl)))
+  if (dependent_type_p (TREE_TYPE (decl))
+      || (processing_template_decl
+	  && VAR_P (decl)
+	  && CP_DECL_THREAD_LOCAL_P (decl)))
     return;
   /* EH specs were not part of the function type prior to c++17, but
      we still can't go pushing dependent eh specs into the namespace.  */
@@ -3471,6 +3474,8 @@ push_local_extern_decl_alias (tree decl)
 	  push_nested_namespace (ns);
 	  alias = do_pushdecl (alias, /* hiding= */true);
 	  pop_nested_namespace (ns);
+	  if (VAR_P (decl) && CP_DECL_THREAD_LOCAL_P (decl))
+	    set_decl_tls_model (alias, DECL_TLS_MODEL (decl));
 	}
     }
 
diff --git a/gcc/testsuite/g++.dg/tls/pr102496-1.C b/gcc/testsuite/g++.dg/tls/pr102496-1.C
new file mode 100644
index 00000000000..8220e1e663a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tls/pr102496-1.C
@@ -0,0 +1,20 @@
+// PR c++/102496
+// { dg-do link { target c++11 } }
+// { dg-require-effective-target tls }
+// { dg-add-options tls }
+// { dg-additional-sources pr102496-2.C }
+
+template <int N>
+int
+foo ()
+{
+  extern __thread int t1;
+  return t1;
+}
+
+int
+main ()
+{
+  extern __thread int t2;
+  return foo <0> () + t2;
+}
diff --git a/gcc/testsuite/g++.dg/tls/pr102496-2.C b/gcc/testsuite/g++.dg/tls/pr102496-2.C
new file mode 100644
index 00000000000..a71a9cddc34
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tls/pr102496-2.C
@@ -0,0 +1,6 @@
+// PR c++/102496
+// { dg-do compile { target c++11 } }
+// { dg-require-effective-target tls }
+
+__thread int t1;
+__thread int t2;