The Google Search optimization team measures changes in terms of millions of CPUs. So if upgrading your compiler saves even 0.1%, well, that's a lot of servers you don't have to buy next year.
"Jun 30, 1987 — The Cray is part of a $20m installation used by Apple's Advanced Technology group and consists of four CPUs operating at 9.5nS per cycle,"
Now we have distcc, that can both massively parallelize compilation, and optimization.
Googles team probably shows some slight improvement, just to justify their work, but in the long run, its just as sloppy as industry wide coding is.
Microsoft is the absolute worst, along with Apple.
