Back in the 90s gcc did a three-stage build to isolate the result from weakness in the vendor native compiler (so, vendor builds gcc0, gcc0 builds gcc1, gcc1 bu

Back in the 90s gcc did a three-stage build to isolate the result from weakness in the vendor native compiler (so, vendor builds gcc0, gcc0 builds gcc1, gcc1 builds gcc2 - and you compare gcc2 to gcc1 to look for problems.) It was popularly considered a "self test suite" until someone did some actual profiling and concluded that gcc only needed about 20% of gcc to compile itself :-)