Add a separate llvm.global_ctors entry for linkonce_odr data initializers

Summary:
These typically come from static data members of class template
specializations.  This accomplishes two things:

1. May expose GlobalOpt optimizations for Itanium C++ ABI code.
2. Works toward fixing double initialization in the Microsoft C++ ABI.

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1475

llvm-svn: 189051

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index d61755c0804..ff06448e5e3 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -278,6 +278,19 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
     OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
     PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
     DelayedCXXInitPosition.erase(D);
+  } else if (D->getInstantiatedFromStaticDataMember()) {
+    // C++ [basic.start.init]p2:
+    //   Defnitions of explicitly specialized class template static data members
+    //   have ordered initialization. Other class template static data members
+    //   (i.e., implicitly or explicitly instantiated specializations) have
+    //   unordered initialization.
+    //
+    // As a consequence, we can put them into their own llvm.global_ctors entry.
+    // This should allow GlobalOpt to fire more often, and allow us to implement
+    // the Microsoft C++ ABI, which uses COMDAT elimination to avoid double
+    // initializaiton.
+    AddGlobalCtor(Fn);
+    DelayedCXXInitPosition.erase(D);
   } else {
     llvm::DenseMap<const Decl *, unsigned>::iterator I =
       DelayedCXXInitPosition.find(D);