ThinLTOBitcodeWriter: Include globals associated with type metadata g…

…lobals in the merged module.

Globals that are associated with globals with type metadata need to appear
in the merged module because they will reference the global's section directly.

Differential Revision: https://reviews.llvm.org/D65312

llvm-svn: 367242

llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp

@@ -218,10 +218,18 @@ void splitAndWriteThinLTOBitcode(
 
   promoteTypeIds(M, ModuleId);
 
-  // Returns whether a global has attached type metadata. Such globals may
-  // participate in CFI or whole-program devirtualization, so they need to
-  // appear in the merged module instead of the thin LTO module.
+  // Returns whether a global or its associated global has attached type
+  // metadata. The former may participate in CFI or whole-program
+  // devirtualization, so they need to appear in the merged module instead of
+  // the thin LTO module. Similarly, globals that are associated with globals
+  // with type metadata need to appear in the merged module because they will
+  // reference the global's section directly.
   auto HasTypeMetadata = [](const GlobalObject *GO) {
+    if (MDNode *MD = GO->getMetadata(LLVMContext::MD_associated))
+      if (auto *AssocVM = dyn_cast_or_null<ValueAsMetadata>(MD->getOperand(0)))
+        if (auto *AssocGO = dyn_cast<GlobalObject>(AssocVM->getValue()))
+          if (AssocGO->hasMetadata(LLVMContext::MD_type))
+            return true;
     return GO->hasMetadata(LLVMContext::MD_type);
   };
 

llvm/test/Transforms/ThinLTOBitcodeWriter/associated.ll

@@ -0,0 +1,14 @@
+; RUN: opt -thinlto-bc -thinlto-split-lto-unit -o %t %s
+; RUN: llvm-modextract -b -n 0 -o - %t | llvm-dis | FileCheck --check-prefix=M0 %s
+; RUN: llvm-modextract -b -n 1 -o - %t | llvm-dis | FileCheck --check-prefix=M1 %s
+
+; M0: @g = external constant
+; M0-NOT: @assoc
+; M1: @g = constant i8 1
+; M1: @assoc = private constant i8 2
+
+@g = constant i8 1, !type !0
+@assoc = private constant i8 2, !associated !1
+
+!0 = !{i32 0, !"typeid"}
+!1 = !{i8* @g}