On Tue, 02 Mar 2010 23:01:01 -0500, Rainer Deyke <[email protected]>
wrote:
On 3/2/2010 14:28, Don wrote:
retard wrote:
Why not dynamic code path selection:
if (cpu_capabilities && SSE4_2)
run_fast_method();
else if (cpu_capabilities && SSE2)
run_medium_fast_method();
else
run_slow_method();
One could also use higher level design patterns like abstract
factories here.
The method needs to be fairly large for that to be beneficial. For
fine-grained stuff, like basic operations on 3D vectors, it doesn't work
at all. And that's one of the primary use cases for SSE.
Why not do it at the largest possible level of granularity?
int main() {
if (cpu_capabilities && SSE4_2) {
return run_fast_main();
} else if (cpu_capabilities && SSE2) {
return run_medium_fast_main();
} else {
return run_slow_main();
}
}
The compiler should be able to do this automatically by compiling every
single function in the program N times with N different code generation
setting. Executable size will skyrocket, but it won't matter because
executable size is rarely a significant concern.
That's great until you start linking, or worse, dynamically linking. Then
you run into some major problems.
