--- a/lib/Support/APSInt.cpp	Wed Feb 18 14:56:07 2015 +0900
+++ b/lib/Support/APSInt.cpp	Tue Oct 13 17:48:58 2015 +0900
@@ -17,6 +17,25 @@
 
 using namespace llvm;
 
+APSInt::APSInt(StringRef Str) {
+  assert(!Str.empty() && "Invalid string length");
+
+  // (Over-)estimate the required number of bits.
+  unsigned NumBits = ((Str.size() * 64) / 19) + 2;
+  APInt Tmp(NumBits, Str, /*Radix=*/10);
+  if (Str[0] == '-') {
+    unsigned MinBits = Tmp.getMinSignedBits();
+    if (MinBits > 0 && MinBits < NumBits)
+      Tmp = Tmp.trunc(MinBits);
+    *this = APSInt(Tmp, /*IsUnsigned=*/false);
+    return;
+  }
+  unsigned ActiveBits = Tmp.getActiveBits();
+  if (ActiveBits > 0 && ActiveBits < NumBits)
+    Tmp = Tmp.trunc(ActiveBits);
+  *this = APSInt(Tmp, /*IsUnsigned=*/true);
+}
+
 void APSInt::Profile(FoldingSetNodeID& ID) const {
   ID.AddInteger((unsigned) (IsUnsigned ? 1 : 0));
   APInt::Profile(ID);