[APFloat] Set losesInfo on no-op convert

[svenvh]

Summary

losesInfo would be left unset when no conversion needs to be done. A
caller such as InstCombine's fitsInFPType would then branch on an
uninitialized value.

Caught using valgrind on an out-of-tree target.

lib/Support/APFloat.cpp

 
 APFloat::APFloat(const fltSemantics &Semantics, StringRef S)
     : APFloat(Semantics) {
   convertFromString(S, rmNearestTiesToEven);
 }
 
 APFloat::opStatus APFloat::convert(const fltSemantics &ToSemantics,
                                    roundingMode RM, bool *losesInfo) {
-  if (&getSemantics() == &ToSemantics)
+  if (&getSemantics() == &ToSemantics) {
+    *losesInfo = false;
     return opOK;
+  }
   if (usesLayout<IEEEFloat>(getSemantics()) &&
       usesLayout<IEEEFloat>(ToSemantics))
     return U.IEEE.convert(ToSemantics, RM, losesInfo);
   if (usesLayout<IEEEFloat>(getSemantics()) &&
       usesLayout<DoubleAPFloat>(ToSemantics)) {
     assert(&ToSemantics == &semPPCDoubleDouble);
     auto Ret = U.IEEE.convert(semPPCDoubleDoubleLegacy, RM, losesInfo);
     *this = APFloat(ToSemantics, U.IEEE.bitcastToAPInt());