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

Richard Smith via cfe-dev cfe-dev at lists.llvm.org
Thu Jul 14 15:38:31 PDT 2016


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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