On Fri, Jun 11, 2021 at 01:56:40PM +0200, David Brown wrote: > If the compiler knows that on the target in question, it is perfectly > safe (i.e., no signals or anything else) to dereference a null pointer, > then in your original "f" the compiler could read *p before it tests p > for null, but it could not do the printf before the test. (Sometimes > for embedded systems the compiler knows that reading via a null pointer > is safe.) But note that this is undefined behaviour in standard C (a null pointer is required to compare unequal to any pointer to any object or function (6.3.2.3/3), and the indirection operator on any operand that does not point to a function or object is undefined behaviour (6.5.3.2/4)). It can be extremely useful to do support this, of course :-) Segher
