The strict aliasing rule in C and C++ governs how pointers of different types can reference the same memory location. Following this rule can enable the compiler to perform aggressive optimizations.

The C standard specifies that it is illegal to access the same memory location using pointers of different types. Specifically, it can only be accessed through

1. A pointer of the same type as what was used to create the object
2. A pointer to a compatible type (like char*)
3. A pointer to a signed/unsigned variant of the type
4. A few other specific exceptions

Following code breaks strict aliasing because an int* accesses memory that was allocated as a float:

float f = 1.0f;
int* p = (int*)&f; // Violates strict aliasing
*p = 0x3f800000;   // Undefined behavior

Breaking strict aliasing can lead to unexpected behavior & bugs or code that works with one compiler but fails with another.

To avoid strict aliasing violations:

• Use proper type punning through unions
• Use memcpy() for type conversions
• Enable compiler warnings with -fstrict-aliasing and -Wstrict-aliasing
• Use -fno-strict-aliasing flag if necessary (disables optimization)

restrict is a type qualifier in C for pointers. It hints to the compiler that for the pointer lifetime, no other pointer will be used to access the object to which it points (helping optimization efforts). If pointer aliasing still occurs, it will result in undefined behavior.