_Occurs at the end of the front-end pass: once for every type involved in template instantiations. The key is a numerical identifier for the type, while the name is its text representation. Type keys are unique within the trace being analyzed. However, different keys coming from different compiler front-end passes may point to the same type. Comparing types between different compiler front-end passes requires using their names. SYMBOLNAME events are emitted at the end of a compiler front-end pass, after all template instantiations have taken place.
As stated in the official docs,
SymbolName:_Occurs at the end of the front-end pass: once for every type involved in template instantiations. The key is a numerical identifier for the type, while the name is its text representation. Type keys are unique within the trace being analyzed. However, different keys coming from different compiler front-end passes may point to the same type. Comparing types between different compiler front-end passes requires using their names. SYMBOLNAME events are emitted at the end of a compiler front-end pass, after all template instantiations have taken place.