[APFloat] APFloat::Storage::Storage - refix use after move

[nickdesaulniers]

Summary

Re-land r360675 after it was reverted in r360770.

This was reported in:
https://llvm.org/reports/scan-build/

Based on feedback in:
https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190513/652286.html

[RKSimon]

cheers - LGTM

[nickdesaulniers]

parting thoughts @eli.friedman ?

[efriedma]

LGTM

llvm/trunk/lib/Support/APFloat.cpp

 } // End detail namespace
 
 APFloat::Storage::Storage(IEEEFloat F, const fltSemantics &Semantics) {
   if (usesLayout<IEEEFloat>(Semantics)) {
     new (&IEEE) IEEEFloat(std::move(F));
     return;
   }
   if (usesLayout<DoubleAPFloat>(Semantics)) {
+    const fltSemantics& S = F.getSemantics();
     new (&Double)
-        DoubleAPFloat(Semantics, APFloat(std::move(F), F.getSemantics()),
+        DoubleAPFloat(Semantics, APFloat(std::move(F), S),
                       APFloat(semIEEEdouble));
     return;
   }
   llvm_unreachable("Unexpected semantics");
 }
 
 APFloat::opStatus APFloat::convertFromString(StringRef Str, roundingMode RM) {
   APFLOAT_DISPATCH_ON_SEMANTICS(convertFromString(Str, RM));