[PATCH] PR c++/77306 - Unable to specify visibility for explicit template instantiations

[PATCH] PR c++/77306 - Unable to specify visibility for explicit template instantiations

[James Abbatiello]

This is my first time attempting a contribution here so please point
out any mistakes.  I've tested this on x86_64-pc-linux-gnu in a VM.

-- 
James Abbatiello


gcc/ChangeLog:

	PR c++/77306
	* attribs.c (decl_attributes): Allow visibility attributes on explicit
	template instantiations.
	* gcc-family/c-attribs.c (handle_visibility_attribute): Likewise.
---
 gcc/attribs.c                               | 3 ++-
 gcc/c-family/c-attribs.c                    | 6 ------
 gcc/testsuite/g++.dg/ext/visibility/warn4.C | 5 +++--
 3 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 55b21271b39..ed1cfa1765b 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -534,7 +534,8 @@ decl_attributes (tree *node, tree attributes, int flags)
 
       if (TYPE_P (*anode)
 	  && (flags & (int) ATTR_FLAG_TYPE_IN_PLACE)
-	  && TYPE_SIZE (*anode) != NULL_TREE)
+	  && TYPE_SIZE (*anode) != NULL_TREE
+	  && !is_attribute_p ("visibility", name))
 	{
 	  warning (OPT_Wattributes, "type attributes ignored after type is already defined");
 	  continue;
diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index f2a88e147ba..e3fb82aef21 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -1895,12 +1895,6 @@ handle_visibility_attribute (tree *node, tree name, tree args,
 		   name);
 	  return NULL_TREE;
 	}
-      else if (TYPE_FIELDS (*node))
-	{
-	  error ("%qE attribute ignored because %qT is already defined",
-		 name, *node);
-	  return NULL_TREE;
-	}
     }
   else if (decl_function_context (decl) != 0 || !TREE_PUBLIC (decl))
     {
diff --git a/gcc/testsuite/g++.dg/ext/visibility/warn4.C b/gcc/testsuite/g++.dg/ext/visibility/warn4.C
index 33e6f678592..a55f9682a12 100644
--- a/gcc/testsuite/g++.dg/ext/visibility/warn4.C
+++ b/gcc/testsuite/g++.dg/ext/visibility/warn4.C
@@ -1,10 +1,11 @@
-// Warn if we try to give an instantiation visibility after it's already
+// Don't warn if we give an instantiation visibility after it's already
 // been instantiated.
 
 // { dg-require-visibility "" }
+// { dg-final { scan-hidden "_ZN1AIdE1fEd" } }
 
 template <class T> struct A { void f (T); };
 template <class T> void A<T>::f (T) { }
 
 A<double> ad;
-template struct __attribute ((visibility ("hidden"))) A<double>; // { dg-warning "already defined" }
+template struct __attribute ((visibility ("hidden"))) A<double>;
-- 
2.11.0

Re: [PATCH] PR c++/77306 - Unable to specify visibility for explicit template instantiations

[James Abbatiello]

On Sat, Apr 22, 2017 at 4:46 PM, James Abbatiello <abbeyj@gmail.com> wrote:
> This is my first time attempting a contribution here so please point
> out any mistakes.  I've tested this on x86_64-pc-linux-gnu in a VM.

Hello,

It has been a few weeks.  Can anybody give me some feedback here or
tell me if I've done something wrong?
https://gcc.gnu.org/ml/gcc-patches/2017-04/msg00975.html

-- 
James Abbatiello

Re: [PATCH] PR c++/77306 - Unable to specify visibility for explicit template instantiations

[Nathan Sidwell]

On 05/21/2017 11:47 PM, James Abbatiello wrote:
> On Sat, Apr 22, 2017 at 4:46 PM, James Abbatiello <abbeyj@gmail.com> wrote:
>> This is my first time attempting a contribution here so please point
>> out any mistakes.  I've tested this on x86_64-pc-linux-gnu in a VM.
> 
> Hello,
> 
> It has been a few weeks.  Can anybody give me some feedback here or
> tell me if I've done something wrong?
> https://gcc.gnu.org/ml/gcc-patches/2017-04/msg00975.html


You're changing the behaviour for all structures -- including the C FE. 
That seems wrong.

Also, AFAICT, youre not changing the visibility for members of the 
struct.  Which also seems incorrect.

nathan


-- 
Nathan Sidwell

Re: [PATCH] PR c++/77306 - Unable to specify visibility for explicit template instantiations

[Jason Merrill]

On Sat, Apr 22, 2017 at 4:46 PM, James Abbatiello <abbeyj@gmail.com> wrote:
>         PR c++/77306
>         * attribs.c (decl_attributes): Allow visibility attributes on explicit
>         template instantiations.
>         * gcc-family/c-attribs.c (handle_visibility_attribute): Likewise.

This doesn't seem sufficient; any members that have already been
instantiated will still have the default visibility.  If you want to
go this way, you'll need to call reset_type_linkage when changing the
visibility of a type that's already defined.

Is there a reason you can't declare the visibility before the first
use of A<double>, e.g.

  extern template struct __attribute ((visibility("hidden"))) A<double>;

followed later by

  template class A<double>;

?

Jason