Fix __uuidof handling on non-type template parameter in C++17

[tzik]

Summary

Clang used to pass the base lvalue of a non-type template parameter
to the template instantiation phase when the base part is __uuidof
and it's running in C++17 mode.
However, that drops its LValuePath, and unintentionally transforms
&__uuidof(...) to __uuidof(...).

This CL fixes that by passing whole expr. Fixes PR24986.

[tzik]

rsmith: Could you PTAL to this?

[thakis]

lgtm, but:

test/SemaCXX/PR24986.cpp

12

Maybe this test could be in test/SemaCXX/ms-uuid.cpp instead?

[tzik]

test/SemaCXX/PR24986.cpp

12

OK, moved there.

[thakis]

r332614, thanks!

lib/Sema/SemaTemplate.cpp

case APValue::LValue: {
       assert(ParamType->isPointerType() || ParamType->isReferenceType() ||
              ParamType->isNullPtrType());
       // -- a temporary object
       // -- a string literal
       // -- the result of a typeid expression, or
       // -- a predefined __func__ variable
       if (auto *E = Value.getLValueBase().dyn_cast<const Expr*>()) {
         if (isa<CXXUuidofExpr>(E)) {
-          Converted = TemplateArgument(const_cast<Expr*>(E));
+          Converted = TemplateArgument(ArgResult.get());
           break;
         }
         Diag(Arg->getLocStart(), diag::err_template_arg_not_decl_ref)
           << Arg->getSourceRange();
         return ExprError();
       }
       auto *VD = const_cast<ValueDecl *>(
           Value.getLValueBase().dyn_cast<const ValueDecl *>());

test/SemaCXX/PR24986.cpp

+// RUN: %clang_cc1 -fsyntax-only -fms-extensions -std=c++17 %s
+
+typedef struct _GUID {} GUID;
+
+template <const GUID* p>
+void f() {
+  const GUID* q = p;
+}
+
+void g() {
+  f<&__uuidof(0)>();
+}