diff mbox

Fix PR c++/69283 (auto deduction fails when ADL is required)

Message ID alpine.DEB.2.20.9.1602051632180.1231@idea
State New
Headers show

Commit Message

Patrick Palka Feb. 5, 2016, 9:36 p.m. UTC 
On Tue, 19 Jan 2016, Patrick Palka wrote:

> On Tue, Jan 19, 2016 at 9:56 AM, Jason Merrill <jason@redhat.com> wrote:
>> On 01/18/2016 10:55 PM, Patrick Palka wrote:
>>>
>>> mark_used is wrongly diagnosing a use of a TEMPLATE_DECL (e.g. the call
>>> to f1 in function f3 of auto-fn29.C below) for having an undeduced
>>> 'auto' return type.  This doesn't make sense, because an 'auto' used
>>> inside a template doesn't get deduced until after the template is
>>> instantiated.  So for a TEMPLATE_DECL we shouldn't diagnose a use of
>>> undeduced 'auto' here.  After instantiation, presumably we will call
>>> mark_used on the resulting FUNCTION_DECL which will check for undeduced
>>> auto appropriately.
>>> @@ -5112,7 +5112,9 @@ mark_used (tree decl, tsubst_flags_t complain)
>>>         || DECL_LANG_SPECIFIC (decl) == NULL
>>>         || DECL_THUNK_P (decl))
>>>       {
>>> -      if (!processing_template_decl && type_uses_auto (TREE_TYPE (decl)))
>>> +      if (!processing_template_decl
>>> +         && TREE_CODE (decl) != TEMPLATE_DECL
>>> +         && type_uses_auto (TREE_TYPE (decl)))
>>
>>
>> How does a TEMPLATE_DECL get in here?  Does it have null DECL_LANG_SPECIFIC?
>
> (In the test case auto-fn29.C,) When instantiating the template
> function f3,we call tsubst on the CALL_EXPR "f1 (v);".  There, ADL is
> performed on the identifier f1 (which is the CALL_EXPR_FN) which
> returns the TEMPLATE_DECL f1.  Then mark_used is called on this
> CALL_EXPR_FN, only if it's a decl.
>
> If in the test case the call to "f1 (v);" is replaced with "Ape::f1
> (v);" then the CALL_EXPR_FN is then an OVERLOAD (to the TEMPLATE_DECL
> f1), i.e. not a decl, so we don't call mark_used on it in tsubst.
>
> The DECL_LANG_SPECIFIC of this decl is not null.
>
>>
>> I'd think mark_used of a TEMPLATE_DECL should return after setting
>> TREE_USED, there's nothing else to do with it.
>
> Consider it changed.

Here's the updated patch, with mark_used made to return earlier in case
of a TEMPLATE_DECL.  Also, auto-fn31.C is now consolidated into
auto-fn29.C since the two test cases were so similar.

-- >8 --

gcc/cp/ChangeLog:

 	PR c++/69283
 	PR c++/67835
 	* decl2.c (mark_used): When given a TEMPLATE_DECL, return after
 	setting its TREE_USED.

gcc/testsuite/ChangeLog:

 	PR c++/69283
 	PR c++/67835
 	* g++.dg/cpp1y/auto-fn29.C: New test.
 	* g++.dg/cpp1y/auto-fn30.C: New test.
---
  gcc/cp/decl2.c                         |  4 ++++
  gcc/testsuite/g++.dg/cpp1y/auto-fn29.C | 34 ++++++++++++++++++++++++++++++++++
  gcc/testsuite/g++.dg/cpp1y/auto-fn30.C | 21 +++++++++++++++++++++
  3 files changed, 59 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn29.C
  create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn30.C

Comments

Jason Merrill Feb. 8, 2016, 6:50 p.m. UTC | #1 
OK.

Jason
diff mbox

Patch

diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index 7d68961..15d7617 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -5068,6 +5068,10 @@  mark_used (tree decl, tsubst_flags_t complain)

    /* Set TREE_USED for the benefit of -Wunused.  */
    TREE_USED (decl) = 1;
+
+  if (TREE_CODE (decl) == TEMPLATE_DECL)
+    return true;
+
    if (DECL_CLONED_FUNCTION_P (decl))
      TREE_USED (DECL_CLONED_FUNCTION (decl)) = 1;

diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn29.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn29.C
new file mode 100644
index 0000000..f9260e0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn29.C
@@ -0,0 +1,34 @@ 
+// PR c++/69283
+// { dg-do compile { target c++14 } }
+
+namespace Ape {
+   struct Type {};
+
+   template <typename T>
+   auto f1(T const& v){
+       return true;
+   }
+
+   template <typename T>
+   auto f2(T const& v){
+       return f2(v); // { dg-error "auto" }
+   }
+}
+
+namespace Baboon {
+   template <typename T>
+   bool f3(T const& v){
+       return f1(v);
+   }
+
+   template <typename T>
+   bool f4(T const& v){
+       f2(v);
+   }
+}
+
+int main(){
+   Ape::Type x;
+   Baboon::f3(x);
+   Baboon::f4(x);
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn30.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn30.C
new file mode 100644
index 0000000..e005e6e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn30.C
@@ -0,0 +1,21 @@ 
+// PR c++/67835
+// { dg-do compile { target c++14 } }
+
+template<class Tag, class T>
+auto g(Tag tag, T x) {
+ return f(tag, x);
+}
+
+namespace abc {
+struct tag {};
+
+struct A {};
+
+template<class T>
+auto f(tag, T x) { return x; }
+}
+
+int main() {
+ g(abc::tag(), abc::A());
+ return 0;
+}