These numbers don't seem abnormal; I recall building Safari many years ago, and having multi-GB of intermediate products shrink down to a 30MB executable (plus a few hundred MB of debug symbol).

So, I have a thought: if we're spending all this time to compile functions (particularly template functions) that are just thrown away later, why are we performing all our optimization passes up-front? Surely, optimization passes in a project like Chrome must eat up a lot of compilation cycles, and if that's literally wasted, why do it in the first place? Can we have a prelink step where we figure out which symbols will eventually make it, and feed that backwards into the compiler?

Maybe a more efficient general approach might be to simply have the optimizer be a thing that runs after the linker, so that the front-end compiler just tries to translate C++ into some intermediate representation as fast as possible. The linker can do the LTO thing, then split the output into multiple chunks for parallelization, and finally merge the optimized chunks back together. With LLVM, it feels like the bitcode makes this a possible compilation approach...