[-cxx-abi microsoft] Mangle user defined entry points properly

Summary:
Functions named "main", "wmain", "WinMain", "wWinMain", and "DllMain"
are never mangled regardless of linkage, even when compiling for kernel
mode.
Depends on D1655

Reviewers: timurrrr, pcc, rnk, whunt

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1670

llvm-svn: 190675

2 files changed, 45 insertions, 2 deletions

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index e082759cb92..9cea06187e2 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -24,6 +24,7 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringSwitch.h"
 
 using namespace clang;
 
@@ -70,6 +71,29 @@ static const FunctionDecl *getStructor(const FunctionDecl *fn) {
   return fn;
 }
 
+// The ABI expects that we would never mangle "typical" user-defined entry
+// points regardless of visibility or freestanding-ness.
+//
+// N.B. This is distinct from asking about "main".  "main" has a lot of special
+// rules associated with it in the standard while these user-defined entry
+// points are outside of the purview of the standard.  For example, there can be
+// only one definition for "main" in a standards compliant program; however
+// nothing forbids the existence of wmain and WinMain in the same translation
+// unit.
+static bool isUserDefinedEntryPoint(const FunctionDecl *FD) {
+  if (!FD->getIdentifier())
+    return false;
+
+  return llvm::StringSwitch<bool>(FD->getName())
+      .Cases("main",     // An ANSI console app
+             "wmain",    // A Unicode console App
+             "WinMain",  // An ANSI GUI app
+             "wWinMain", // A Unicode GUI app
+             "DllMain",  // A DLL
+             true)
+      .Default(false);
+}
+
 /// MicrosoftCXXNameMangler - Manage the mangling of a single name for the
 /// Microsoft Visual C++ ABI.
 class MicrosoftCXXNameMangler {
@@ -230,8 +254,7 @@ bool MicrosoftMangleContext::shouldMangleDeclName(const NamedDecl *D) {
     if (FD->hasAttr<OverloadableAttr>())
       return true;
 
-    // "main" is not mangled.
-    if (FD->isMain())
+    if (isUserDefinedEntryPoint(FD))
       return false;
 
     // C++ functions and those whose names are not a simple identifier need
diff --git a/clang/test/CodeGenCXX/mangle-ms.cpp b/clang/test/CodeGenCXX/mangle-ms.cpp
index e7450d8fb0f..8b7aa4223d9 100644
--- a/clang/test/CodeGenCXX/mangle-ms.cpp
+++ b/clang/test/CodeGenCXX/mangle-ms.cpp
@@ -255,3 +255,23 @@ extern "C" inline void extern_c_func() {
 void call_extern_c_func() {
   extern_c_func();
 }
+
+int main() { return 0; }
+// CHECK-DAG: @main
+// X64-DAG:   @main
+
+int wmain() { return 0; }
+// CHECK-DAG: @wmain
+// X64-DAG:   @wmain
+
+int WinMain() { return 0; }
+// CHECK-DAG: @WinMain
+// X64-DAG:   @WinMain
+
+int wWinMain() { return 0; }
+// CHECK-DAG: @wWinMain
+// X64-DAG:   @wWinMain
+
+int DllMain() { return 0; }
+// CHECK-DAG: @DllMain
+// X64-DAG:   @DllMain