[APFloat] Fix IsInteger() for DoubleAPFloat.

Previously, we would just assert instead.

Differential Revision:  https://reviews.llvm.org/D36961

llvm-svn: 311351
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index deb76cb..f835bd1 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -4363,10 +4363,7 @@
 
 bool DoubleAPFloat::isInteger() const {
   assert(Semantics == &semPPCDoubleDouble && "Unexpected Semantics");
-  APFloat Tmp(semPPCDoubleDoubleLegacy);
-  (void)Tmp.add(Floats[0], rmNearestTiesToEven);
-  (void)Tmp.add(Floats[1], rmNearestTiesToEven);
-  return Tmp.isInteger();
+  return Floats[0].isInteger() && Floats[1].isInteger();
 }
 
 void DoubleAPFloat::toString(SmallVectorImpl<char> &Str,