[PATCH] D65312: ThinLTOBitcodeWriter: Include globals associated with type metadata globals in the merged module.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added a reviewer: tejohnson.
Herald added subscribers: dexonsmith, steven_wu, hiraditya, inglorion, mehdi_amini.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D65312

Files:
  llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
  llvm/test/Transforms/ThinLTOBitcodeWriter/associated.ll


Index: llvm/test/Transforms/ThinLTOBitcodeWriter/associated.ll
===================================================================
--- /dev/null
+++ 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
+
+ at g = constant i8 1, !type !0
+ at assoc = private constant i8 2, !associated !1
+
+!0 = !{i32 0, !"typeid"}
+!1 = !{i8* @g}
Index: llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
===================================================================
--- llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
+++ llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
@@ -218,10 +218,18 @@
 
   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);
   };
 


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