> What compiler optimizations have the biggest impact on scientific / floating point computation?
In my experience, auto-vectorization is the big one. Modern CPUs do 2-, 4-, or 8-wide operations, but it can be hard to convince the compiler to use them. Next is loop tiling, to keep things in cache(s) where possible. These are both hard to do by hand.
Loop interchange to get better locality is nice, but can be done by hand without much trouble by someone who understands computers.
In my experience, auto-vectorization is the big one. Modern CPUs do 2-, 4-, or 8-wide operations, but it can be hard to convince the compiler to use them. Next is loop tiling, to keep things in cache(s) where possible. These are both hard to do by hand.
Loop interchange to get better locality is nice, but can be done by hand without much trouble by someone who understands computers.