Move vtable type metadata emission behind a cc1-level flag.

In ThinLTO mode, type metadata will require the module to be written as a
multi-module bitcode file, which is currently incompatible with the Darwin
linker. It is also useful to be able to enable or disable multi-module bitcode
for testing purposes. This introduces a cc1-level flag, -f{,no-}lto-unit,
which is used by the driver to enable multi-module bitcode on all but
Darwin+ThinLTO, and can also be used to enable/disable the feature manually.

Differential Revision: https://reviews.llvm.org/D28877

llvm-svn: 292448

1 files changed, 9 insertions, 1 deletions

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 78672b2544f..e7c6f22c95d 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -4238,8 +4238,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     if (JA.getType() == types::TY_LLVM_BC)
       CmdArgs.push_back("-emit-llvm-uselists");
 
-    if (D.isUsingLTO())
+    if (D.isUsingLTO()) {
       Args.AddLastArg(CmdArgs, options::OPT_flto, options::OPT_flto_EQ);
+
+      // The Darwin linker currently uses the legacy LTO API, which does not
+      // support LTO unit features (CFI, whole program vtable opt) under
+      // ThinLTO.
+      if (!getToolChain().getTriple().isOSDarwin() ||
+          D.getLTOMode() == LTOK_Full)
+        CmdArgs.push_back("-flto-unit");
+    }
   }
 
   if (const Arg *A = Args.getLastArg(options::OPT_fthinlto_index_EQ)) {