Index: lib/CodeGen/CGDeclCXX.cpp
===================================================================
--- lib/CodeGen/CGDeclCXX.cpp
+++ lib/CodeGen/CGDeclCXX.cpp
@@ -409,21 +409,25 @@
       AddGlobalCtor(Fn, Priority);
     }
   }
-  
-  // Include the filename in the symbol name. Including "sub_" matches gcc and
-  // makes sure these symbols appear lexicographically behind the symbols with
-  // priority emitted above.
+
+  llvm::Function *Fn = nullptr;
   SourceManager &SM = Context.getSourceManager();
-  SmallString<128> FileName(llvm::sys::path::filename(
-      SM.getFileEntryForID(SM.getMainFileID())->getName()));
-  for (size_t i = 0; i < FileName.size(); ++i) {
-    // Replace everything that's not [a-zA-Z0-9._] with a _. This set happens
-    // to be the set of C preprocessing numbers.
-    if (!isPreprocessingNumberBody(FileName[i]))
-      FileName[i] = '_';
+  if (const FileEntry *MainFile = SM.getFileEntryForID(SM.getMainFileID())) {
+    // Include the filename in the symbol name. Including "sub_" matches gcc and
+    // makes sure these symbols appear lexicographically behind the symbols with
+    // priority emitted above.
+    SmallString<128> FileName(llvm::sys::path::filename(MainFile->getName()));
+    for (size_t i = 0; i < FileName.size(); ++i) {
+      // Replace everything that's not [a-zA-Z0-9._] with a _. This set happens
+      // to be the set of C preprocessing numbers.
+      if (!isPreprocessingNumberBody(FileName[i]))
+        FileName[i] = '_';
+    }
+    Fn = CreateGlobalInitOrDestructFunction(
+        *this, FTy, llvm::Twine("_GLOBAL__sub_I_", FileName));
+  } else {
+    Fn = CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__sub_I__null_");
   }
-  llvm::Function *Fn = CreateGlobalInitOrDestructFunction(
-      *this, FTy, llvm::Twine("_GLOBAL__sub_I_", FileName));
 
   CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, CXXGlobalInits);
   AddGlobalCtor(Fn);
Index: unittests/CMakeLists.txt
===================================================================
--- unittests/CMakeLists.txt
+++ unittests/CMakeLists.txt
@@ -20,6 +20,7 @@
 add_subdirectory(Tooling)
 add_subdirectory(Format)
 add_subdirectory(Sema)
+add_subdirectory(CodeGen)
 # FIXME: Why are the libclang unit tests disabled on Windows?
 if(NOT WIN32) 
   add_subdirectory(libclang)
Index: unittests/CodeGen/BufferSourceTest.cpp
===================================================================
--- /dev/null
+++ unittests/CodeGen/BufferSourceTest.cpp
@@ -0,0 +1,78 @@
+//===- unittests/CodeGen/BufferSourceTest.cpp - MemoryBuffer source tests -===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/ASTConsumer.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Lex/Preprocessor.h"
+#include "clang/CodeGen/ModuleBuilder.h"
+#include "clang/Sema/Sema.h"
+#include "clang/Parse/ParseAST.h"
+#include "clang/Basic/TargetInfo.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Support/Host.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/IR/LLVMContext.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace clang;
+
+namespace {
+
+// Emitting constructors for global objects involves looking
+// at the source file name. This makes sure that we don't crash
+// if the source file is a memory buffer.
+const char *TestProgram =
+    "class EmitCXXGlobalInitFunc    "
+    "{                              "
+    "public:                        "
+    "   EmitCXXGlobalInitFunc() {}  "
+    "};                             "
+    "EmitCXXGlobalInitFunc test;    ";
+
+TEST(BufferSourceTest, EmitCXXGlobalInitFunc) {
+    CompilerInstance *compiler = new CompilerInstance;
+
+    compiler->createDiagnostics();
+    compiler->getLangOpts().CPlusPlus = 1;
+    compiler->getLangOpts().CPlusPlus11 = 1;
+
+    compiler->getTargetOpts().Triple = llvm::Triple::normalize(
+        llvm::sys::getProcessTriple());
+    compiler->setTarget(clang::TargetInfo::CreateTargetInfo(
+      compiler->getDiagnostics(),
+      std::make_shared<clang::TargetOptions>(
+        compiler->getTargetOpts())));
+
+    compiler->createFileManager();
+    compiler->createSourceManager(compiler->getFileManager());
+    compiler->createPreprocessor(clang::TU_Prefix);
+
+    compiler->createASTContext();
+
+    compiler->setASTConsumer(std::unique_ptr<ASTConsumer>(
+        CreateLLVMCodeGen(
+            compiler->getDiagnostics(),
+            "EmitCXXGlobalInitFuncTest",
+            compiler->getCodeGenOpts(),
+            compiler->getTargetOpts(),
+            llvm::getGlobalContext())));
+
+    compiler->createSema(clang::TU_Prefix,NULL);
+
+    clang::SourceManager &sm = compiler->getSourceManager();
+    sm.setMainFileID(sm.createFileID(
+        llvm::MemoryBuffer::getMemBuffer(TestProgram), clang::SrcMgr::C_User));
+
+    clang::ParseAST(compiler->getSema(), false, false);
+}
+
+}
\ No newline at end of file
Index: unittests/CodeGen/CMakeLists.txt
===================================================================
--- /dev/null
+++ unittests/CodeGen/CMakeLists.txt
@@ -0,0 +1,17 @@
+set(LLVM_LINK_COMPONENTS
+  Support
+  )
+
+add_clang_unittest(CodegenTests
+  BufferSourceTest.cpp
+  )
+
+target_link_libraries(CodegenTests
+  clangAST
+  clangBasic
+  clangFrontend
+  clangParse
+  clangSema
+  clangTooling
+  clangCodegen
+  )
Index: unittests/CodeGen/Makefile
===================================================================
--- /dev/null
+++ unittests/CodeGen/Makefile
@@ -0,0 +1,20 @@
+##===- unittests/CodeGen/Makefile --------------------------*- Makefile -*-===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is distributed under the University of Illinois Open Source
+# License. See LICENSE.TXT for details.
+#
+##===----------------------------------------------------------------------===##
+
+CLANG_LEVEL = ../..
+TESTNAME = CodeGen
+include $(CLANG_LEVEL)/../../Makefile.config
+LINK_COMPONENTS := $(TARGETS_TO_BUILD) asmparser bitreader support mc option
+USEDLIBS = clangTooling.a clangFrontend.a clangSerialization.a clangDriver.a \
+           clangRewrite.a clangRewriteFrontend.a \
+           clangParse.a clangSema.a clangAnalysis.a \
+           clangEdit.a clangAST.a clangASTMatchers.a clangLex.a clangBasic.a \
+           clangCodeGen.a
+
+include $(CLANG_LEVEL)/unittests/Makefile
Index: unittests/Makefile
===================================================================
--- unittests/Makefile
+++ unittests/Makefile
@@ -14,7 +14,8 @@
 
 IS_UNITTEST_LEVEL := 1
 CLANG_LEVEL := ..
-PARALLEL_DIRS = Basic Lex Driver libclang Format ASTMatchers AST Tooling Sema
+PARALLEL_DIRS = CodeGen Basic Lex Driver libclang Format ASTMatchers AST Tooling \
+	        Sema
 
 include $(CLANG_LEVEL)/../..//Makefile.config