I'll dig into the article, but out front there is something I don't understand. What is this second, trusted compiler? How did we get that? Why not just use tha

I'll dig into the article, but out front there is something I don't understand. What is this second, trusted compiler? How did we get that? Why not just use that and its results, rather than vetting foreign compilers...? EDIT: Reading, but I think I'm having more questions, not less. The compiler source could introduces optimizations into the compiler binary's output that could be used to recompile the source again and get a _better_ binary right? The article speaks of compiling the source once with the the foreign compiler and then again with its results; but, on the trusted side it seems to be saying you just do one compilation and you don't compile the source again with the result of that compilation. Seems like you'd have to use the same measures on both sides before comparing binaries?