Introduce the notion of instantiation dependence into Clang's AST. A

type/expression/template argument/etc. is instantiation-dependent if
it somehow involves a template parameter, even if it doesn't meet the
requirements for the more common kinds of dependence (dependent type,
type-dependent expression, value-dependent expression).

When we see an instantiation-dependent type, we know we always need to
perform substitution into that instantiation-dependent type. This
keeps us from short-circuiting evaluation in places where we
shouldn't, and lets us properly implement C++0x [temp.type]p2.

In theory, this would also allow us to properly mangle
instantiation-dependent-but-not-dependent decltype types per the
Itanium C++ ABI, but we aren't quite there because we still mangle
based on the canonical type in cases like, e.g.,

  template<unsigned> struct A { };
  template<typename T>
    void f(A<sizeof(sizeof(decltype(T() + T())))>) { }
  template void f<int>(A<sizeof(sizeof(int))>);

and therefore get the wrong answer.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134225 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/AST/NestedNameSpecifier.cpp b/lib/AST/NestedNameSpecifier.cpp
index 2878dff3ed..f6d4f2513c 100644
--- a/lib/AST/NestedNameSpecifier.cpp
+++ b/lib/AST/NestedNameSpecifier.cpp
@@ -174,6 +174,28 @@ bool NestedNameSpecifier::isDependent() const {
   return false;
 }
 
+/// \brief Whether this nested name specifier refers to a dependent
+/// type or not.
+bool NestedNameSpecifier::isInstantiationDependent() const {
+  switch (getKind()) {
+  case Identifier:
+    // Identifier specifiers always represent dependent types
+    return true;
+    
+  case Namespace:
+  case NamespaceAlias:
+  case Global:
+    return false;
+    
+  case TypeSpec:
+  case TypeSpecWithTemplate:
+    return getAsType()->isInstantiationDependentType();
+  }
+  
+  // Necessary to suppress a GCC warning.
+  return false;
+}
+
 bool NestedNameSpecifier::containsUnexpandedParameterPack() const {
   switch (getKind()) {
   case Identifier: