Revert 117660. Apparently it's not as trivial as that...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117663 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 857352b..b09dcd0 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -236,9 +236,9 @@
 
 
   bool isMemMode5() const {
+    // FIXME: Is this right?  What about postindexed and Writeback?
     if (!isMemory() || Mem.OffsetIsReg || Mem.OffsetRegShifted ||
-        Mem.Preindexed || Mem.Negative || Mem.Postindexed ||
-        Mem.Writeback)
+        Mem.Preindexed || Mem.Negative)
       return false;
 
     return true;