From 1023668bc2d625e7bb5c3ee776175d4e031b6e97 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Thu, 2 Jul 2015 09:43:11 +0000
Subject: [PATCH] [MS ABI] nullptr data member ptrs are mangled differently for
 classes vs fns

It turns out that nullptr pointers to data members act differently in
function templates vs class templates.  Class templates use a variable
width representation proportional to the number of fields needed to
materialize it.  Function templates always use a single '0' template
parameter.  However, using '0' all the time is problematic if the class
uses single or multiple inheritance.  In those cases, use -1.

llvm-svn: 241251
---
 clang/lib/AST/MicrosoftMangle.cpp              | 18 +++++++++++++++---
 .../mangle-ms-templates-memptrs-2.cpp          | 15 +++++++++++++++
 .../CodeGenCXX/mangle-ms-templates-memptrs.cpp |  4 ++--
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index c50db60abe5a..48a8fa541a69 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -1215,11 +1215,23 @@ void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
         return;
       }
       if (MPT->isMemberDataPointer()) {
-        mangleMemberDataPointer(RD, nullptr);
-        return;
+        if (isa<ClassTemplateDecl>(TD)) {
+          mangleMemberDataPointer(RD, nullptr);
+          return;
+        }
+        // nullptr data pointers are always represented with a single field
+        // which is initialized with either 0 or -1.  Why -1?  Well, we need to
+        // distinguish the case where the data member is at offset zero in the
+        // record.
+        // However, we are free to use 0 *if* we would use multiple fields for
+        // non-nullptr member pointers.
+        if (!RD->nullFieldOffsetIsZero()) {
+          mangleIntegerLiteral(llvm::APSInt::get(-1), /*IsBoolean=*/false);
+          return;
+        }
       }
     }
-    Out << "$0A@";
+    mangleIntegerLiteral(llvm::APSInt::getUnsigned(0), /*IsBoolean=*/false);
     break;
   }
   case TemplateArgument::Expression:
diff --git a/clang/test/CodeGenCXX/mangle-ms-templates-memptrs-2.cpp b/clang/test/CodeGenCXX/mangle-ms-templates-memptrs-2.cpp
index e2cbe15dfa9f..b01d6099d8f7 100644
--- a/clang/test/CodeGenCXX/mangle-ms-templates-memptrs-2.cpp
+++ b/clang/test/CodeGenCXX/mangle-ms-templates-memptrs-2.cpp
@@ -3,22 +3,37 @@
 template <typename T, int (T::*)() = nullptr>
 struct J {};
 
+template <typename T, int T::* = nullptr>
+struct K {};
+
 struct __single_inheritance M;
 J<M> m;
 // CHECK-DAG: @"\01?m@@3U?$J@UM@@$0A@@@A"
 
+K<M> m2;
+// CHECK-DAG: @"\01?m2@@3U?$K@UM@@$0?0@@A"
+
 struct __multiple_inheritance N;
 J<N> n;
 // CHECK-DAG: @"\01?n@@3U?$J@UN@@$HA@@@A"
 
+K<N> n2;
+// CHECK-DAG: @"\01?n2@@3U?$K@UN@@$0?0@@A"
+
 struct __virtual_inheritance O;
 J<O> o;
 // CHECK-DAG: @"\01?o@@3U?$J@UO@@$IA@A@@@A"
 
+K<O> o2;
+// CHECK-DAG: @"\01?o2@@3U?$K@UO@@$FA@?0@@A"
+
 struct P;
 J<P> p;
 // CHECK-DAG: @"\01?p@@3U?$J@UP@@$JA@A@?0@@A"
 
+K<P> p2;
+// CHECK-DAG: @"\01?p2@@3U?$K@UP@@$GA@A@?0@@A"
+
 #pragma pointers_to_members(full_generality, virtual_inheritance)
 
 struct S {
diff --git a/clang/test/CodeGenCXX/mangle-ms-templates-memptrs.cpp b/clang/test/CodeGenCXX/mangle-ms-templates-memptrs.cpp
index 42237f5b7d4a..e710abe97e98 100644
--- a/clang/test/CodeGenCXX/mangle-ms-templates-memptrs.cpp
+++ b/clang/test/CodeGenCXX/mangle-ms-templates-memptrs.cpp
@@ -69,8 +69,8 @@ void ReadFields() {
 // them right in class templates.
 // CHECK: call {{.*}} @"\01??$ReadField@US@@$0A@@@YAHAAUS@@@Z"
 // CHECK: call {{.*}} @"\01??$ReadField@UM@@$0A@@@YAHAAUM@@@Z"
-// CHECK: call {{.*}} @"\01??$ReadField@UV@@$FA@?0@@YAHAAUV@@@Z"
-// CHECK: call {{.*}} @"\01??$ReadField@UU@@$GA@A@?0@@YAHAAUU@@@Z"
+// CHECK: call {{.*}} @"\01??$ReadField@UV@@$0A@@@YAHAAUV@@@Z"
+// CHECK: call {{.*}} @"\01??$ReadField@UU@@$0A@@@YAHAAUU@@@Z"
 
 // Non-polymorphic null data memptr vs first field memptr.  MSVC mangles these
 // the same.