r193203 - Sema: Allow IndirectFieldDecl to appear in a non-type template argument

[David Majnemer]

On Tue, Oct 22, 2013 at 3:43 PM, Richard Smith <richard at metafoo.co.uk>wrote:

> On Tue, Oct 22, 2013 at 2:56 PM, David Majnemer <david.majnemer at gmail.com>wrote:
>
>> Author: majnemer
>> Date: Tue Oct 22 16:56:38 2013
>> New Revision: 193203
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=193203&view=rev
>> Log:
>> Sema: Allow IndirectFieldDecl to appear in a non-type template argument
>>
>> We would not identify pointer-to-member construction in a non-type
>> template argument if it was either a FieldDecl or a CXXMethodDecl.
>> However, this would incorrectly reject declarations that were injected
>> via an IndirectFieldDecl (e.g. a field inside of an anonymous union).
>>
>
> Is this really correct? Such fields are not members of the enclosing
> non-anonymous struct. &Z::union_member below should have type "int
> Z::<anonymous union>::*", not "int Z::*", as far as I can tell.
>

GCC, EDG and MSVC all seem to think it should be allowed.

Note that we allowed the following related test case before my change:
struct a {
  union { int i; };
};

template <int (a::*)> struct b;
constexpr auto z = &a::i;
typedef b<z> c;

Do you consider this ill-formed as well?


> This fixes PR17657.
>>
>> Modified:
>>     cfe/trunk/lib/Sema/SemaTemplate.cpp
>>     cfe/trunk/test/SemaTemplate/temp_arg_nontype.cpp
>>
>> Modified: cfe/trunk/lib/Sema/SemaTemplate.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaTemplate.cpp?rev=193203&r1=193202&r2=193203&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/lib/Sema/SemaTemplate.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaTemplate.cpp Tue Oct 22 16:56:38 2013
>> @@ -4609,8 +4609,11 @@ static bool CheckTemplateArgumentPointer
>>                    diag::err_template_arg_not_pointer_to_member_form)
>>        << Arg->getSourceRange();
>>
>> -  if (isa<FieldDecl>(DRE->getDecl()) ||
>> isa<CXXMethodDecl>(DRE->getDecl())) {
>> +  if (isa<FieldDecl>(DRE->getDecl()) ||
>> +      isa<IndirectFieldDecl>(DRE->getDecl()) ||
>> +      isa<CXXMethodDecl>(DRE->getDecl())) {
>>      assert((isa<FieldDecl>(DRE->getDecl()) ||
>> +            isa<IndirectFieldDecl>(DRE->getDecl()) ||
>>              !cast<CXXMethodDecl>(DRE->getDecl())->isStatic()) &&
>>             "Only non-static member pointers can make it here");
>>
>>
>> Modified: cfe/trunk/test/SemaTemplate/temp_arg_nontype.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaTemplate/temp_arg_nontype.cpp?rev=193203&r1=193202&r2=193203&view=diff
>>
>> ==============================================================================
>> --- cfe/trunk/test/SemaTemplate/temp_arg_nontype.cpp (original)
>> +++ cfe/trunk/test/SemaTemplate/temp_arg_nontype.cpp Tue Oct 22 16:56:38
>> 2013
>> @@ -75,6 +75,9 @@ struct Z {
>>
>>    int int_member;
>>    float float_member;
>> +  union {
>> +    int union_member;
>> +  };
>>  };
>>  template<int (Z::*pmf)(int)> struct A6; // expected-note{{template
>> parameter is declared here}}
>>  A6<&Z::foo> *a17_1;
>> @@ -88,6 +91,7 @@ A7<&Z::int_member> *a18_1;
>>  A7c<&Z::int_member> *a18_2;
>>  A7<&Z::float_member> *a18_3; // expected-error{{non-type template
>> argument of type 'float Z::*' cannot be converted to a value of type 'int
>> Z::*'}}
>>  A7c<(&Z::int_member)> *a18_4; // expected-warning{{address non-type
>> template argument cannot be surrounded by parentheses}}
>> +A7c<&Z::union_member> *a18_5;
>>
>
> Can we mangle this?
>

We can't mangle it yet but there is no reason to see why we couldn't. EDG
and GCC both disagree on what it should be mangled to. EDG sticks in __Cn
where n corresponds to the depth of the anonymous unions if they are
nested, GCC mangles it as {unnamed type#1}.  I believe neither are correct,
the Itanium ABI 5.1.2 General Structure section states that the name of an
anonymous union comes from "the first named data member found by a
pre-order, depth-first, declaration-order walk of the data members of the
anonymous union".


>
>
>>  template<unsigned char C> struct Overflow; // expected-note{{template
>> parameter is declared here}}
>>
>>
>>
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>>
>
>
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