Driver: Handle /GR- in a compatible way with MSVC

There are slight differences between /GR- and -fno-rtti which made
mapping one to the other inappropriate.

-fno-rtti disables dynamic_cast, typeid, and does not emit RTTI related
information for the v-table.

/GR- does not generate complete object locators and thus will not
reference them in vftables.  However, constructs like dynamic_cast and
typeid are permitted.

This should bring our implementation of RTTI up to semantic parity with
MSVC modulo bugs.

llvm-svn: 212138
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 8238167..35affab 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -4193,15 +4193,7 @@
       (InputType == types::TY_C || InputType == types::TY_CXX)) {
     Command *CLCommand = getCLFallback()->GetCommand(C, JA, Output, Inputs,
                                                      Args, LinkingOutput);
-    // RTTI support in clang-cl is a work in progress.  Fall back to MSVC early
-    // if we are using 'clang-cl /fallback /GR'.
-    // FIXME: Remove this when RTTI is finished.
-    if (Args.hasFlag(options::OPT_frtti, options::OPT_fno_rtti, false)) {
-      D.Diag(diag::warn_drv_rtti_fallback) << CLCommand->getExecutable();
-      C.addCommand(CLCommand);
-    } else {
-      C.addCommand(new FallbackCommand(JA, *this, Exec, CmdArgs, CLCommand));
-    }
+    C.addCommand(new FallbackCommand(JA, *this, Exec, CmdArgs, CLCommand));
   } else {
     C.addCommand(new Command(JA, *this, Exec, CmdArgs));
   }
@@ -4446,9 +4438,10 @@
   if (Arg *A = Args.getLastArg(options::OPT_show_includes))
     A->render(Args, CmdArgs);
 
-  // RTTI is currently not supported, so disable it by default.
-  if (!Args.hasArg(options::OPT_frtti, options::OPT_fno_rtti))
-    CmdArgs.push_back("-fno-rtti");
+  // This controls whether or not we emit RTTI data for polymorphic types.
+  if (Args.hasFlag(options::OPT__SLASH_GR_, options::OPT__SLASH_GR,
+                   /*default=*/false))
+    CmdArgs.push_back("-fno-rtti-data");
 
   const Driver &D = getToolChain().getDriver();
   EHFlags EH = parseClangCLEHFlags(D, Args);
@@ -7709,9 +7702,9 @@
   // Flags for which clang-cl have an alias.
   // FIXME: How can we ensure this stays in sync with relevant clang-cl options?
 
-  if (Arg *A = Args.getLastArg(options::OPT_frtti, options::OPT_fno_rtti))
-    CmdArgs.push_back(A->getOption().getID() == options::OPT_frtti ? "/GR"
-                                                                   : "/GR-");
+  if (Args.hasFlag(options::OPT__SLASH_GR_, options::OPT__SLASH_GR,
+                   /*default=*/false))
+    CmdArgs.push_back("/GR-");
   if (Arg *A = Args.getLastArg(options::OPT_ffunction_sections,
                                options::OPT_fno_function_sections))
     CmdArgs.push_back(A->getOption().getID() == options::OPT_ffunction_sections