[PATCH] D118980: Don't dllexport reference temporaries

[Hans Wennborg via Phabricator via cfe-commits]

hans created this revision.
hans added reviewers: thakis, mstorsjo, rnk.
hans requested review of this revision.
Herald added a project: clang.

Even if the reference itself is dllexport, the temporary should not be -- in fact, we're already giving it internal linkage, so dllexporting it is not just wasteful, but will fail to link, as in the example below:

  $ cat /tmp/a.cc
  void _DllMainCRTStartup() {}
  const int __declspec(dllexport) &foo = 42;
  
  $ clang-cl -fuse-ld=lld /tmp/a.cc /Zl /link /dll /out:a.dll
  lld-link: error: <root>: undefined symbol: int const &foo::$RT1


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118980

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGenCXX/reference-temporary-ms.cpp


Index: clang/test/CodeGenCXX/reference-temporary-ms.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/reference-temporary-ms.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - -triple=i386-pc-win32 -fms-extensions | FileCheck %s
+
+const int __declspec(dllexport) &Exported = 42;
+
+// The reference temporary shouldn't be dllexport, even if the reference is.
+// CHECK: @"?$RT1 at Exported@@3ABHB" = internal constant i32 42
+
+// CHECK: @"?Exported@@3ABHB" = dso_local dllexport constant i32* @"?$RT1 at Exported@@3ABHB"
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -5725,6 +5725,9 @@
       /*InsertBefore=*/nullptr, llvm::GlobalVariable::NotThreadLocal, TargetAS);
   if (emitter) emitter->finalize(GV);
   setGVProperties(GV, VD);
+  if (GV->getDLLStorageClass() == llvm::GlobalVariable::DLLExportStorageClass)
+    // The reference temporary should never be dllexport.
+    GV->setDLLStorageClass(llvm::GlobalVariable::DefaultStorageClass);
   GV->setAlignment(Align.getAsAlign());
   if (supportsCOMDAT() && GV->isWeakForLinker())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));


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