From 3ab5a9cd1c826b627d6bcc775df824f637dd9e17 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <rnk@google.com>
Date: Wed, 26 Dec 2018 20:07:52 +0000
Subject: [PATCH] [MS] Mangle return adjusting thunks with the public access
 specifier

MSVC does this, so we should too.

Fixes PR40138

llvm-svn: 350071
---
 clang/lib/AST/MicrosoftMangle.cpp                  | 18 +++++++++-----
 .../test/CodeGenCXX/mangle-ms-thunks-covariant.cpp | 29 ++++++++++++++++++++++
 2 files changed, 41 insertions(+), 6 deletions(-)
 create mode 100644 clang/test/CodeGenCXX/mangle-ms-thunks-covariant.cpp

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index caa3af59..92e9679 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -2939,14 +2939,14 @@ void MicrosoftMangleContextImpl::mangleCXXName(const NamedDecl *D,
 // <vtordisp-shift>     ::= <offset-to-vtordisp>
 // <vtordispex-shift>   ::= <offset-to-vbptr> <vbase-offset-offset>
 //                          <offset-to-vtordisp>
-static void mangleThunkThisAdjustment(const CXXMethodDecl *MD,
+static void mangleThunkThisAdjustment(AccessSpecifier AS,
                                       const ThisAdjustment &Adjustment,
                                       MicrosoftCXXNameMangler &Mangler,
                                       raw_ostream &Out) {
   if (!Adjustment.Virtual.isEmpty()) {
     Out << '$';
     char AccessSpec;
-    switch (MD->getAccess()) {
+    switch (AS) {
     case AS_none:
       llvm_unreachable("Unsupported access specifier");
     case AS_private:
@@ -2974,7 +2974,7 @@ static void mangleThunkThisAdjustment(const CXXMethodDecl *MD,
       Mangler.mangleNumber(-static_cast<uint32_t>(Adjustment.NonVirtual));
     }
   } else if (Adjustment.NonVirtual != 0) {
-    switch (MD->getAccess()) {
+    switch (AS) {
     case AS_none:
       llvm_unreachable("Unsupported access specifier");
     case AS_private:
@@ -2988,7 +2988,7 @@ static void mangleThunkThisAdjustment(const CXXMethodDecl *MD,
     }
     Mangler.mangleNumber(-static_cast<uint32_t>(Adjustment.NonVirtual));
   } else {
-    switch (MD->getAccess()) {
+    switch (AS) {
     case AS_none:
       llvm_unreachable("Unsupported access specifier");
     case AS_private:
@@ -3019,7 +3019,13 @@ void MicrosoftMangleContextImpl::mangleThunk(const CXXMethodDecl *MD,
   MicrosoftCXXNameMangler Mangler(*this, MHO);
   Mangler.getStream() << '?';
   Mangler.mangleName(MD);
-  mangleThunkThisAdjustment(MD, Thunk.This, Mangler, MHO);
+
+  // Usually the thunk uses the access specifier of the new method, but if this
+  // is a covariant return thunk, then MSVC always uses the public access
+  // specifier, and we do the same.
+  AccessSpecifier AS = Thunk.Return.isEmpty() ? MD->getAccess() : AS_public;
+  mangleThunkThisAdjustment(AS, Thunk.This, Mangler, MHO);
+
   if (!Thunk.Return.isEmpty())
     assert(Thunk.Method != nullptr &&
            "Thunk info should hold the overridee decl");
@@ -3040,7 +3046,7 @@ void MicrosoftMangleContextImpl::mangleCXXDtorThunk(
   MicrosoftCXXNameMangler Mangler(*this, MHO, DD, Type);
   Mangler.getStream() << "??_E";
   Mangler.mangleName(DD->getParent());
-  mangleThunkThisAdjustment(DD, Adjustment, Mangler, MHO);
+  mangleThunkThisAdjustment(DD->getAccess(), Adjustment, Mangler, MHO);
   Mangler.mangleFunctionType(DD->getType()->castAs<FunctionProtoType>(), DD);
 }
 
diff --git a/clang/test/CodeGenCXX/mangle-ms-thunks-covariant.cpp b/clang/test/CodeGenCXX/mangle-ms-thunks-covariant.cpp
new file mode 100644
index 0000000..47b1a38
--- /dev/null
+++ b/clang/test/CodeGenCXX/mangle-ms-thunks-covariant.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -fno-rtti-data -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=x86_64-pc-win32 -fms-compatibility-version=19.00 | FileCheck %s --check-prefix=CHECK
+
+namespace t1 {
+struct A {
+public:
+  virtual ~A();
+  virtual A *f();
+};
+struct B {
+public:
+  virtual ~B();
+
+private:
+  virtual B *f();
+};
+struct C : A, B {
+  virtual ~C();
+
+protected:
+  virtual C *f();
+};
+C c;
+}
+// Main external C::f impl:
+// CHECK-DAG: "?f@C@t1@@MEAAPEAU12@XZ"
+// New slot in C's vftable for B, returns C* directly:
+// CHECK-DAG: "?f@C@t1@@O7EAAPEAU12@XZ"
+// Return-adjusting thunk in C's vftable for B:
+// CHECK-DAG: "?f@C@t1@@W7EAAPEAUB@2@XZ"
-- 
2.7.4