[gcc r14-8960] c++: variable partial spec redeclaration [PR113612]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:19ac327de421fe05916e234e3450e6e1cc5c935c

commit r14-8960-g19ac327de421fe05916e234e3450e6e1cc5c935c
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Feb 12 21:00:53 2024 -0500

    c++: variable partial spec redeclaration [PR113612]
    
    If register_specialization finds a previous declaration and throws the new
    one away, we shouldn't still add the new one to
    DECL_TEMPLATE_SPECIALIZATIONS.
    
            PR c++/113612
    
    gcc/cp/ChangeLog:
    
            * pt.cc (process_partial_specialization): Return early
            on redeclaration.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1y/var-templ85.C: New test.

Diff:
---
 gcc/cp/pt.cc                             | 11 ++++++++---
 gcc/testsuite/g++.dg/cpp1y/var-templ85.C |  6 ++++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 475f2181cc49..2803824d11e1 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -5417,9 +5417,14 @@ process_partial_specialization (tree decl)
     }
 
   if (VAR_P (decl))
-    /* We didn't register this in check_explicit_specialization so we could
-       wait until the constraints were set.  */
-    decl = register_specialization (decl, maintmpl, specargs, false, 0);
+    {
+      /* We didn't register this in check_explicit_specialization so we could
+	 wait until the constraints were set.  */
+      tree reg = register_specialization (decl, maintmpl, specargs, false, 0);
+      if (reg != decl)
+	/* Redeclaration.  */
+	return reg;
+    }
   else
     associate_classtype_constraints (type);
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ85.C b/gcc/testsuite/g++.dg/cpp1y/var-templ85.C
new file mode 100644
index 000000000000..33c24e0c2844
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ85.C
@@ -0,0 +1,6 @@
+// PR c++/113612
+// { dg-do compile { target c++14 } }
+
+template <typename T> T t;
+template <typename T> extern T *t<T *>;
+template <typename T> T *t<T *> = t<int>;