Consider what `stalin' does in about 3300 lines of Scheme
code. It translates R4RS scheme to C and takes a lot of time
doing so but the code is generates is blazingly fast. The
kind of globally optimized C code you or I wouldn't have the
patience to write. Or the ability to keep all that context in
one's head to do as good a job. Stalin compiles itself to
over 660K lines of C code! Then you give this C code to gcc
and it munches away for many minutes and finally dies on a
2GB system! If gcc was capable of only doing peephole
optimizing, it would've been able to generate code much more
quickly and without need gigabytes of memory.