[cfe-dev] Fwd: AST contains "type-dependent" for non-dependency

[Matthias Gehre via cfe-dev]

I proposed a patch for this here: https://reviews.llvm.org/D22476

2016-07-15 0:38 GMT+02:00 Richard Smith <richard at metafoo.co.uk>:

> On Thu, Jul 14, 2016 at 3:07 PM, Matthias Gehre via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi everyone,
>>
>> I don't understand why the AST for
>>
>> template <int Index> struct B {
>>   int independent() {
>>     return x[2];
>>   }
>>   std::array<int,3> x;
>> };
>>
>> is
>>
>> |-ClassTemplateDecl 0x27faf20 <line:89:1, line:104:1> line:89:29 B
>> | |-NonTypeTemplateParmDecl 0x27fae20 <col:11, col:15> col:15 referenced
>> 'int' Index
>> | |-CXXRecordDecl 0x27fae90 <col:22, line:104:1> line:89:29 struct B
>> definition
>> | | |-CXXRecordDecl 0x27fb1b8 <col:22, col:29> col:29 implicit struct B
>> | | |-CXXMethodDecl 0x27fb2d0 <line:90:3, line:94:3> line:90:7
>> independent 'int (void)'
>> | | | `-CompoundStmt 0x27fc430 <col:21, line:94:3>
>> | | |   `-ReturnStmt 0x27fc418 <line:91:5, col:16>
>> | | |     `-ArraySubscriptExpr 0x27fc3f0 <col:12, col:16> '<dependent
>> type>' lvalue
>> | | |       |-MemberExpr 0x27fc378 <col:12> 'std::array<int, 3>':'struct
>> std::array<int, 3>' lvalue ->x 0x27fc318
>> | | |       | `-CXXThisExpr 0x27fc360 <col:12> 'B<Index> *' this
>> | | |       `-IntegerLiteral 0x27fc3b0 <col:15> 'int' 2
>>
>> Especially, why do we have the ArraySubscriptExpr '<dependent type>'?
>>
>> When specializing to B<0>, the ArraySubscriptExpr becomes a
>> CXXOperatorCallExpr as expected:
>>
>> | |-ClassTemplateSpecializationDecl 0x27fc610 <line:89:1, line:104:1>
>> line:89:29 struct B definition
>> | | |-TemplateArgument integral 0
>> | | |-CXXRecordDecl 0x27fc878 prev 0x27fc610 <col:22, col:29> col:29
>> implicit struct B
>> | | |-CXXMethodDecl 0x27fc908 <line:90:3, line:94:3> line:90:7 used
>> independent 'int (void)'
>> | | | `-CompoundStmt 0x2800648 <col:21, line:94:3>
>> | | |   `-ReturnStmt 0x2800630 <line:91:5, col:16>
>> | | |     `-ImplicitCastExpr 0x2800618 <col:12, col:16> 'int':'int'
>> <LValueToRValue>
>> | | |       `-CXXOperatorCallExpr 0x28005d0 <col:12, col:16> 'int':'int'
>> lvalue
>> | | |         |-ImplicitCastExpr 0x28005b8 <col:12, col:16> 'int
>> &(*)(size_t)' <FunctionToPointerDecay>
>> | | |         | `-DeclRefExpr 0x2800590 <col:12, col:16> 'int &(size_t)'
>> lvalue CXXMethod 0x27fb870 'operator[]' 'int &(size_t)'
>> | | |         |-MemberExpr 0x2800540 <col:12> 'std::array<int,
>> 3>':'struct std::array<int, 3>' lvalue ->x 0x27fca78
>> | | |         | `-CXXThisExpr 0x2800528 <col:12> 'struct B<0> *' this
>> | | |         `-ImplicitCastExpr 0x2800578 <col:14, col:15>
>> 'size_t':'unsigned long' <IntegralCast>
>> | | |           `-IntegerLiteral 0x27fc3b0 <col:15> 'int' 2
>>
>> Why is the AST for the template and the specialization different? The
>> method does not depend on the template parameter.
>>
>
> Yes, this is wrong; we don't correctly implement the type-dependence rules
> for class member access expressions specified in core issue 224 (see
> http://clang.llvm.org/cxx_dr_status.html#224, http://wg21.link/cwg224).
>
>
>> Thanks for any hints,
>>
>> Matthias
>>
>>
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>>
>>
>
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