[pushed] c++: variable partial spec redeclaration [PR113612]

[Jason Merrill]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- 8< --

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.
---
 gcc/cp/pt.cc                             | 11 ++++++++---
 gcc/testsuite/g++.dg/cpp1y/var-templ85.C |  6 ++++++
 2 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ85.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 9c225c095c8..8bef2f8f6a2 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 00000000000..33c24e0c284
--- /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>;

base-commit: f29f7f86935e29786bf9f976ec99d7639b381b14
-- 
2.43.0