Which is faster : if (bool) or if(int)?

Question

Which value is better to use? Boolean true or Integer 1?

The above topic made me do some experiments with bool and in

Answer 1

Makes sense to me. Your compiler apparently defines a bool as an 8-bit value, and your system ABI requires it to "promote" small (< 32-bit) integer arguments to 32-bit when pushing them onto the call stack. So to compare a bool, the compiler generates code to isolate the least significant byte of the 32-bit argument that g receives, and compares it with cmpb. In the first example, the int argument uses the full 32 bits that were pushed onto the stack, so it simply compares against the whole thing with cmpl.

Answer 2

With GCC 4.5 on Linux and Windows at least, sizeof(bool) == 1. On x86 and x86_64, you can't pass in less than an general purpose register's worth to a function (whether via the stack or a register depending on the calling convention etc...).

So the code for bool, when un-optimized, actually goes to some length to extract that bool value from the argument stack (using another stack slot to save that byte). It's more complicated than just pulling a native register-sized variable.