diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 3e768f25317..31300aea569 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Target/TargetRegistry.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/OwningPtr.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
@@ -1661,17 +1662,11 @@ parseRegisterList(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
   Parser.Lex(); // Eat right curly brace token.
 
   // Verify the register list.
-  SmallVectorImpl<std::pair<unsigned, SMLoc> >::const_iterator
-    RI = Registers.begin(), RE = Registers.end();
-
-  unsigned HighRegNum = getARMRegisterNumbering(RI->first);
   bool EmittedWarning = false;
-
-  DenseMap<unsigned, bool> RegMap;
-  RegMap[HighRegNum] = true;
-
-  for (++RI; RI != RE; ++RI) {
-    const std::pair<unsigned, SMLoc> &RegInfo = *RI;
+  unsigned HighRegNum = 0;
+  BitVector RegMap(32);
+  for (unsigned i = 0, e = Registers.size(); i != e; ++i) {
+    const std::pair<unsigned, SMLoc> &RegInfo = Registers[i];
     unsigned Reg = getARMRegisterNumbering(RegInfo.first);
 
     if (RegMap[Reg]) {
@@ -1683,7 +1678,7 @@ parseRegisterList(SmallVectorImpl<MCParsedAsmOperand*> &Operands) {
       Warning(RegInfo.second,
               "register not in ascending order in register list");
 
-    RegMap[Reg] = true;
+    RegMap.set(Reg);
     HighRegNum = std::max(Reg, HighRegNum);
   }