[PATCH] AST: Mangle nullptr properly in template args for the Itanium ABI

[David Majnemer]

    - Address Richard's review comments.

Hi rsmith, rjmccall, eli.friedman, doug.gregor,

http://llvm-reviews.chandlerc.com/D1625

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D1625?vs=4124&id=4129#toc

Files:
  docs/ReleaseNotes.rst
  lib/AST/ItaniumMangle.cpp
  test/CodeGenCXX/mangle-nullptr-arg.cpp

Index: docs/ReleaseNotes.rst
===================================================================
--- docs/ReleaseNotes.rst
+++ docs/ReleaseNotes.rst
@@ -81,7 +81,10 @@
   member offsets for classes inheriting from certain classes with tail padding.
   See PR16537.
 
-- ...
+- Fixed non-conformance with the Itanium C++ ABI wherein the external name
+  generated for a template parameter of type std::nullptr_t with a corresponding
+  template argument of nullptr would be incorrect. This is an ABI breaking
+  change. See PR17141.
 
 C++11 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
Index: lib/AST/ItaniumMangle.cpp
===================================================================
--- lib/AST/ItaniumMangle.cpp
+++ lib/AST/ItaniumMangle.cpp
@@ -3337,10 +3337,15 @@
     break;
   }
   case TemplateArgument::NullPtr: {
+    //  <expr-primary> ::= L <nullptr type> E
     //  <expr-primary> ::= L <type> 0 E
-    Out << 'L';
-    mangleType(A.getNullPtrType());
-    Out << "0E";
+    if (A.getNullPtrType()->isNullPtrType())
+      Out << "LDnE";
+    else {
+      Out << 'L';
+      mangleType(A.getNullPtrType());
+      Out << "0E";
+    }
     break;
   }
   case TemplateArgument::Pack: {
Index: test/CodeGenCXX/mangle-nullptr-arg.cpp
===================================================================
--- test/CodeGenCXX/mangle-nullptr-arg.cpp
+++ test/CodeGenCXX/mangle-nullptr-arg.cpp
@@ -14,3 +14,8 @@
 // CHECK-LABEL: define void @_Z5test316DependentTypePtrIPiLS0_0EE
 template<typename T, T x> struct DependentTypePtr {};
 void test3(DependentTypePtr<int*,nullptr>) { }
+
+template<decltype(nullptr)> struct NP {};
+
+// CHECK-LABEL: define void @_Z5test42NPILDnEE
+void test4(NP<nullptr>) {}
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