Re-land the fix for PR7139.

llvm-svn: 104446
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 7b0c316..18c69121 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -582,14 +582,10 @@
     llvm::Value *Null = llvm::Constant::getNullValue(CGF.ConvertType(T));
     CGF.EmitStoreThroughLValue(RValue::get(Null), LV, T);
   } else {
-    // Otherwise, just memset the whole thing to zero.  This is legal
-    // because in LLVM, all default initializers are guaranteed to have a
-    // bit pattern of all zeros.
-    // FIXME: That isn't true for member pointers!
     // There's a potential optimization opportunity in combining
     // memsets; that would be easy for arrays, but relatively
     // difficult for structures with the current code.
-    CGF.EmitMemSetToZero(LV.getAddress(), T);
+    CGF.EmitNullInitialization(LV.getAddress(), T);
   }
 }