[AST] Fix a crash on mangling a binding decl from a DeclRefExpr.

[rsmith]

Here's a testcase that produces a name with external linkage:

struct X { int i, j; };
auto [a,b] = X{1,2};
template<typename T> void f(decltype(a + T())) {}
template void f<int>(int);

We should make sure that we mangle the reference to a as _Z1aE here.

[hokein]

add one more test.

[hokein]

In D86130#2224757, @rsmith wrote:

Here's a testcase that produces a name with external linkage:

struct X { int i, j; };
auto [a,b] = X{1,2};
template<typename T> void f(decltype(a + T())) {}
template void f<int>(int);

We should make sure that we mangle the reference to a as _Z1aE here.

Thanks, added.

clang/lib/AST/ItaniumMangle.cpp

else if (const VarDecl *VD = dyn_cast<VarDecl>(GD.getDecl()))
     mangleName(VD);
   else if (const IndirectFieldDecl *IFD =
                dyn_cast<IndirectFieldDecl>(GD.getDecl()))
     mangleName(IFD->getAnonField());
   else if (const FieldDecl *FD = dyn_cast<FieldDecl>(GD.getDecl()))
     mangleName(FD);
   else if (const MSGuidDecl *GuidD = dyn_cast<MSGuidDecl>(GD.getDecl()))
     mangleName(GuidD);
+  else if (const BindingDecl *BD = dyn_cast<BindingDecl>(GD.getDecl()))
+    mangleName(BD);
   else
     llvm_unreachable("unexpected kind of global decl");
 }
 
 void CXXNameMangler::mangleFunctionEncoding(GlobalDecl GD) {
   const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
   // <encoding> ::= <function name> <bare-function-type>
 

clang/test/CodeGenCXX/mangle.cpp

namespace test58 {
   } a;
   template <class T> struct identity { typedef T type; };
   struct A {
    template <typename T> A(T, bool (identity<T>::type::*)());
   };
   // CHECK-LABEL: @_ZN6test581AC1INS_5StateEEET_MNS_8identityIS3_E4typeEFbvE
   void fn1() { A(a, &State::m_fn1); }
 }
+
+namespace test59 {
+  // verify no crash.
+  template<typename T>
+  void f(T g) {
+    auto [e] = g;
+    [](decltype(e)) {};
+  }
+}
+
+namespace test60 {
+  struct X { int i, j; };
+  auto [a,b] = X{1,2};
+  template<typename T> void f(decltype(a + T())) {}
+  // CHECK-LABEL: @_ZN6test601fIiEEvDTplL_ZNS_1aEEcvT__EE
+  template void f<int>(int);
+}