reduce stack emptiness checking

Author: grisumbras

include/boost/json/impl/serializer.hpp

@@ -67,16 +67,18 @@ bool
 serialize_write(writer& w, stream& ss0, integral_conversion_tag )
 {
     value jv;
-    if(StackEmpty || w.st_.empty())
+    BOOST_IF_CONSTEXPR( StackEmpty )
     {
+        BOOST_ASSERT( w.st_.empty() );
         auto const pt = reinterpret_cast<T const*>(w.p_);
         // as this is a number, we don't need the value to outlive the call,
         // so we can use this local variable
         jv = *pt;
         w.p_ = &jv;
+        return serialize_write<true, value>(w, ss0);
     }
 
-    return serialize_write<StackEmpty, value>(w, ss0);
+    return serialize_write<false, value>(w, ss0);
 }
 
 template<bool StackEmpty, class T>
@@ -90,15 +92,17 @@ serialize_write(writer& w, stream& ss0, sequence_conversion_tag )
     local_stream ss(ss0);
     ConstIterator it;
     ConstIterator end;
-    if(StackEmpty || w.st_.empty())
+    BOOST_IF_CONSTEXPR( StackEmpty )
     {
+        BOOST_ASSERT( w.st_.empty() );
         BOOST_ASSERT( w.p_ );
         pt = reinterpret_cast<T const*>(w.p_);
         it = pt->begin();
         end = pt->end();
     }
     else
     {
+        BOOST_ASSERT( !w.st_.empty() );
         writer::state st;
         w.st_.pop(st);
         w.st_.pop(it);
@@ -114,6 +118,8 @@ serialize_write(writer& w, stream& ss0, sequence_conversion_tag )
             break;
         }
     }
+
+    goto do_arr1;
 do_arr1:
     if(BOOST_JSON_LIKELY(ss))
         ss.append('[');
@@ -125,17 +131,29 @@ serialize_write(writer& w, stream& ss0, sequence_conversion_tag )
     for(;;)
     {
         w.p_ = &*it;
+        if( true )
+        {
+            if( !serialize_write<true, Value>(w, ss) )
+                return w.suspend(writer::state::arr2, it, pt);
+        }
+        else
+        {
+    goto do_arr2;
 do_arr2:
-        if( !serialize_write<StackEmpty, Value>(w, ss) )
-            return w.suspend(writer::state::arr2, it, pt);
+            if( !serialize_write<false, Value>(w, ss) )
+                return w.suspend(writer::state::arr2, it, pt);
+        }
         if(BOOST_JSON_UNLIKELY( ++it == end ))
             break;
+
+    goto do_arr3;
 do_arr3:
         if(BOOST_JSON_LIKELY(ss))
             ss.append(',');
         else
             return w.suspend(writer::state::arr3, it, pt);
     }
+
 do_arr4:
     if(BOOST_JSON_LIKELY(ss))
         ss.append(']');