pieniek <edek.pienkowski@xxxxxxxxx> writes: > if a loop contains if-s on a constant boolean, will gcc create two > loop versions, for the boolean being true and the boolean being false, > if the boolean switches on some heavy code (in this case, costly > debugging code)? The boolean in question being not a template param or > not really const either, just constant during the loop run. > > I do understand that if the boolean is off (no heavy code) this does > boils down to a couple of jumps not taken or taken, but, with these > ifs removed, the loop can benefit from things like > vectorisation. Right? > > So, the question rephrased, is there any benefit of templating some > function containing a loop based on the bool value (or writing the > code in both versions anyhow)? The goal would be to make the fast > (call it release) version of the loop really fast. This optimization is called loop unswitching. You can enable it in gcc with the -funswitch-loops option. This option is turned on by -O3, but not by -O2. Ian
