OSX: Make sure T.mangleof matches the final mangle for C++ symbols

By using upstream's Target.prefixName(), which prepends an additional
underscore on OSX/Darwin for C++ symbols.
We then need to prevent LLVM from implicitly prepending a third one.

ddmd/target.d

@@ -84,25 +84,6 @@ struct Target
     static bool isVectorOpSupported(Type type, TOK op, Type t2 = null);
     // CTFE support for cross-compilation.
     static Expression paintAsType(Expression e, Type type);
-    // ABI and backend.
-    static void loadModule(Module m);
-    static void prefixName(OutBuffer *buf, LINK linkage);
-
-    static const(char)* toCppMangle(Dsymbol s)
-    {
-        if (isTargetWindowsMSVC())
-            return toCppMangleMSVC(s);
-        else
-            return toCppMangleItanium(s);
-    }
-
-    static const(char)* cppTypeInfoMangle(ClassDeclaration cd)
-    {
-        if (isTargetWindowsMSVC())
-            return cppTypeInfoMangleMSVC(cd);
-        else
-            return cppTypeInfoMangleItanium(cd);
-    }
   }
   else // !IN_LLVM
   {
@@ -445,6 +426,7 @@ struct Target
             assert(0);
         }
     }
+  } // !IN_LLVM
 
     /******************************
      * For the given module, perform any post parsing analysis.
@@ -474,6 +456,15 @@ struct Target
     }
 
     extern (C++) static const(char)* toCppMangle(Dsymbol s)
+    {
+      version(IN_LLVM)
+      {
+        if (isTargetWindowsMSVC())
+            return toCppMangleMSVC(s);
+        else
+            return toCppMangleItanium(s);
+      }
+      else
       {
         static if (TARGET_LINUX || TARGET_OSX || TARGET_FREEBSD || TARGET_OPENBSD || TARGET_SOLARIS)
             return toCppMangleItanium(s);
@@ -482,8 +473,18 @@ struct Target
         else
             static assert(0, "fix this");
       }
+    }
 
     extern (C++) static const(char)* cppTypeInfoMangle(ClassDeclaration cd)
+    {
+      version(IN_LLVM)
+      {
+          if (isTargetWindowsMSVC())
+              return cppTypeInfoMangleMSVC(cd);
+          else
+              return cppTypeInfoMangleItanium(cd);
+      }
+      else
       {
         static if (TARGET_LINUX || TARGET_OSX || TARGET_FREEBSD || TARGET_OPENBSD || TARGET_SOLARIS)
             return cppTypeInfoMangleItanium(cd);
@@ -492,7 +493,7 @@ struct Target
         else
             static assert(0, "fix this");
       }
-  } // !IN_LLVM
+    }
 
     /**
      * For a vendor-specific type, return a string containing the C++ mangling.

gen/abi-x86-64.cpp

@@ -207,6 +207,18 @@ struct X86_64TargetABI : TargetABI {
   X86_64_C_struct_rewrite struct_rewrite;
   ImplicitByvalRewrite byvalRewrite;
 
+  std::string mangleFunctionForLLVM(std::string name, LINK l) override {
+    if (l == LINKcpp && global.params.isOSX) {
+      // Prepend a 0x1 byte to prevent LLVM from prepending an underscore.
+      return name.insert(0, "\1");
+    }
+    return name;
+  }
+
+  std::string mangleVariableForLLVM(std::string name, LINK l) override {
+    return mangleFunctionForLLVM(std::move(name), l);
+  }
+
   bool returnInArg(TypeFunction *tf) override;
 
   bool passByVal(Type *t) override;

gen/abi-x86.cpp

@@ -63,7 +63,7 @@ struct X86TargetABI : TargetABI {
     case LINKwindows:
       return name;
     case LINKcpp:
-      if (global.params.targetTriple->isOSWindows()) {
+      if (global.params.isWindows || global.params.isOSX) {
         // Prepend a 0x1 byte to prevent LLVM from prepending an underscore.
         return name.insert(0, "\1");
       }
@@ -90,7 +90,7 @@ struct X86TargetABI : TargetABI {
     case LINKwindows:
       return name;
     case LINKcpp:
-      if (global.params.targetTriple->isOSWindows()) {
+      if (global.params.isWindows || global.params.isOSX) {
         // Prepend a 0x1 byte to prevent LLVM from prepending an underscore.
         return name.insert(0, "\1");
       }

gen/naked.cpp

@@ -160,12 +160,14 @@ void DtoDefineNakedFunction(FuncDeclaration *fd) {
   bool const isOSX = (triple.getOS() == llvm::Triple::Darwin ||
                       triple.getOS() == llvm::Triple::MacOSX);
 
-  // osx is different
-  // also mangling has an extra underscore prefixed
+  // OSX is different
   if (isOSX) {
+    // extra leading underscore except for extern(C++)
+    if (fd->linkage != LINKcpp) {
       fullmangle += '_';
       fullmangle += mangle;
       mangle = fullmangle.c_str();
+    }
 
     std::string section = "text";
     bool weak = false;

gen/target.cpp

@@ -226,7 +226,7 @@ Expression *Target::paintAsType(Expression *e, Type *type) {
     break;
 
   default:
-    assert(0);
+    llvm_unreachable("Unsupported source type");
   }
 
   switch (type->ty) {
@@ -245,21 +245,6 @@ Expression *Target::paintAsType(Expression *e, Type *type) {
     return createRealExp(e->loc, u.float64value, type);
 
   default:
-    assert(0);
+    llvm_unreachable("Unsupported target type");
   }
-
-  return nullptr; // avoid warning
 }
-
-/******************************
- * For the given module, perform any post parsing analysis.
- * Certain compiler backends (ie: GDC) have special placeholder
- * modules whose source are empty, but code gets injected
- * immediately after loading.
- */
-void Target::loadModule(Module *m) {}
-
-/******************************
- *
- */
-void Target::prefixName(OutBuffer *buf, LINK linkage) {}