Index: lib/Target/TargetLoweringObjectFile.cpp
===================================================================
--- lib/Target/TargetLoweringObjectFile.cpp
+++ lib/Target/TargetLoweringObjectFile.cpp
@@ -58,8 +58,16 @@
   const Constant *C = GV->getInitializer();
 
   // Must have zero initializer.
-  if (!C->isNullValue())
-    return false;
+  if (!C->isNullValue() && !isa<UndefValue>(C)) {
+    if (!isa<ConstantAggregate>(C))
+      return false;
+    // Check that it isn't all zeros or undefs.
+    for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
+      Constant *E = cast<Constant>(C->getOperand(i));
+      if (!E->isNullValue() && !isa<UndefValue>(E))
+        return false;
+    }
+  }
 
   // Leave constant zeros in readonly constant sections, so they can be shared.
   if (GV->isConstant())
Index: test/CodeGen/X86/undef-globals-bss.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/undef-globals-bss.ll
@@ -0,0 +1,8 @@
+; RUN: llc < %s | FileCheck %s
+target triple = "x86_64-apple-darwin"
+
+; CHECK: .zerofill __DATA,__bss,_vals,8000000,2 ## @vals
+@vals = internal unnamed_addr global [2000000 x i32] undef, align 4
+
+; CHECK: .zerofill __DATA,__bss,_struct,8000016,3 ## @struct
+@struct = internal global { i1, [8000000 x i8], [7 x i8], i64 } { i1 false, [8000000 x i8] zeroinitializer, [7 x i8] undef, i64 0 }, align 8