On 17 July 2016 at 23:27, greg7mdp wrote: > I want to use the gcc builtin __builtin_popcount() inside my program if, and > only if, the program is compiled with the option -mpopcnt. > > This is because I see that calling __builtin_popcount() when the program is > not compiled with option -mpopcnt is actually slower than doing the popcnt() > computation myself. > > So I was hoping that there is a way to test whether a compilation option is > present in the preprocessor. Anyone know the answer? You can't test whether the option was given on the command-line, but that's not the right thing to test anyway. What you can test is whether use of the instruction is enabled, by checking for the __POPCNT__ macro being defined.
