Added StrictVTablePointers linking requirement

[Prazek]

Summary

Generates code like this
!llvm.module.flags = !{!0, !1}

!0 = !{i32 1, !"StrictVTablePointers", i32 1}
!1 = !{i32 3, !"StrictVTablePointersRequirement", !2}
!2 = !{!"StrictVTablePointers", i32 1}

[rsmith]

Functionally LGTM, but please add a test case. Is there any precedent for how to spell these module flags (StrictVTablePointers / strict_vtable_pointers / strict.vtable.pointers)?

[Prazek]

I see that CGObjCMac.cpp names it like this:

"Objective-C Garbage Collection"

[rsmith]

LGTM

lib/CodeGen/CodeGenModule.cpp

if (CodeGenOpts.DwarfVersion) {
     // We can change from Warning to Latest if such mode is supported.
     getModule().addModuleFlag(llvm::Module::Warning, "Dwarf Version",
                               CodeGenOpts.DwarfVersion);
   }
   if (CodeGenOpts.EmitCodeView) {
     // Indicate that we want CodeView in the metadata.
     getModule().addModuleFlag(llvm::Module::Warning, "CodeView", 1);
   }
+  if (CodeGenOpts.OptimizationLevel > 0 && CodeGenOpts.StrictVTablePointers) {
+    // We don't support LTO with 2 with different StrictVTablePointers
+    // FIXME: we could support it by stripping all the information introduced
+    // by StrictVTablePointers.
+
+    getModule().addModuleFlag(llvm::Module::Error, "StrictVTablePointers",1);
+
+    llvm::Metadata *Ops[2] = {
+              llvm::MDString::get(VMContext, "StrictVTablePointers"),
+              llvm::ConstantAsMetadata::get(llvm::ConstantInt::get(
+                  llvm::Type::getInt32Ty(VMContext), 1))};
+
+    getModule().addModuleFlag(llvm::Module::Require,
+                              "StrictVTablePointersRequirement",
+                              llvm::MDNode::get(VMContext, Ops));
+  }
   if (DebugInfo)
     // We support a single version in the linked module. The LLVM
     // parser will drop debug info with a different version number
     // (and warn about it, too).
     getModule().addModuleFlag(llvm::Module::Warning, "Debug Info Version",
                               llvm::DEBUG_METADATA_VERSION);
 
   // We need to record the widths of enums and wchar_t, so that we can generate