[cfe-dev] _Atomic qualified types and template argument deduction

Rachel Craik via cfe-dev cfe-dev at lists.llvm.org
Thu Sep 3 09:58:10 PDT 2015

Hi Hubert,

Yes, I'll take a look.



From:	Hubert Tong <hubert.reinterpretcast at gmail.com>
To:	Rachel Craik/Toronto/IBM at IBMCA
Cc:	Richard Smith <richard at metafoo.co.uk>, Clang Dev
            <cfe-dev at lists.llvm.org>
Date:	09/02/2015 05:02 PM
Subject:	Re: [cfe-dev] _Atomic qualified types and template argument

Hi Rachel,

I believe you might be interested in picking this one up?

-- HT

On Wed, Sep 2, 2015 at 1:52 PM, Richard Smith <richard at metafoo.co.uk>
  On Wed, Sep 2, 2015 at 9:29 AM, Hubert Tong via cfe-dev <
  cfe-dev at lists.llvm.org> wrote:
   In C11, the lvalue conversions replace atomic types with the
   unqualified, non-atomic version. This is similar to the array-to-pointer
   and function-to-pointer conversions in C++.

   I believe that this parallel should be reflected in template argument
   deduction (specifically, in the place in [temp.deduct.call] where
   array-to-pointer and function-to-pointer conversion is mentioned).

   That is, I believe the following should compile successfully (Clang
   doesn't do so at this time):
   extern _Atomic const int x;
   template <typename T> struct C { typedef T type; };
   template <typename T> C<T> foo(T);
   extern decltype(foo(x))::type chk;
   extern int chk;

   Comments welcome.

  I agree. The intent of [temp.deduct.call]p2 and p3 seems to be that if P
  is not a reference, then A is replaced by the type obtained by converting
  A to a prvalue (and dropping qualifiers). Whether we view _Atomic as a
  funny kind of qualifier or as a funny kind of modifier that decays to its
  underlying type, we should deduce T = int in your above example.
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