[clang][bytecode] Avoid a getValue() call in builtin_isinf (llvm#152939)

Get the APFloat once and work with that, instead of calling isInf() and
potentially isNegative().

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -459,12 +459,13 @@ static bool interp__builtin_isinf(InterpState &S, CodePtr OpPC,
                                   const InterpFrame *Frame, bool CheckSign,
                                   const CallExpr *Call) {
   const Floating &Arg = S.Stk.pop<Floating>();
-  bool IsInf = Arg.isInf();
+  APFloat F = Arg.getAPFloat();
+  bool IsInf = F.isInfinity();
 
   if (CheckSign)
-    pushInteger(S, IsInf ? (Arg.isNegative() ? -1 : 1) : 0, Call->getType());
+    pushInteger(S, IsInf ? (F.isNegative() ? -1 : 1) : 0, Call->getType());
   else
-    pushInteger(S, Arg.isInf(), Call->getType());
+    pushInteger(S, IsInf, Call->getType());
   return true;
 }