[clang] 853e0aa - Don't dllexport reference temporaries

[Hans Wennborg via cfe-commits]

Author: Hans Wennborg
Date: 2022-02-04T16:31:51+01:00
New Revision: 853e0aa424e40b80d0bda1dd8a3471a361048e4b

URL: https://github.com/llvm/llvm-project/commit/853e0aa424e40b80d0bda1dd8a3471a361048e4b
DIFF: https://github.com/llvm/llvm-project/commit/853e0aa424e40b80d0bda1dd8a3471a361048e4b.diff

LOG: Don't dllexport reference temporaries

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

Differential revision: https://reviews.llvm.org/D118980

Added: 
    clang/test/CodeGenCXX/reference-temporary-ms.cpp

Modified: 
    clang/lib/CodeGen/CodeGenModule.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 2346176a15628..5ffb954642a6b 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5725,6 +5725,9 @@ ConstantAddress CodeGenModule::GetAddrOfGlobalTemporary(
       /*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()));

diff  --git a/clang/test/CodeGenCXX/reference-temporary-ms.cpp b/clang/test/CodeGenCXX/reference-temporary-ms.cpp
new file mode 100644
index 0000000000000..dd12ad8ec59f9
--- /dev/null
+++ b/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"