Pointer aliasing occurs when two pointers of different types point to the same memory location. This can lead to unexpected behavior and incorrect results when optimizing code. By default, the compiler assumes that pointer aliasing can occur and takes necessary precautions to handle it correctly.

However, with the -fstrict-aliasing option, the compiler assumes strict pointer aliasing rules. This means that it can make more aggressive optimizations, assuming that pointers of different types will not alias each other. This can improve performance by enabling the compiler to generate more efficient code.

It is important to note that enabling strict aliasing can also have side effects. If code violates strict aliasing rules, it can lead to undefined behavior. For example, if a pointer of one type is used to access memory through a pointer of another type, it can result in incorrect behavior or crashes.

To enable strict aliasing in GCC, you can use the -fstrict-aliasing flag when compiling your code:

gcc -fstrict-aliasing myfile.c -o myfile

Similarly, in C++ with GCC, you can use:

g++ -fstrict-aliasing myfile.cpp -o myfile

In conclusion, the -fstrict-aliasing flag is a compiler option that allows the compiler to make assumptions about pointer aliasing. It can improve code optimization but may also lead to undefined behavior if strict aliasing rules are violated.