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10 C and C++ Source-Level Optimizations Chapter 2
25112 Rev. 3.06 September 2005
Software Optimization Guide for AMD64 Processors
2.2 Using Arrays and Pointers
Optimization
Use array notation instead of pointer notation when working with arrays.
Application
This optimization applies to:
• 32-bit software
• 64-bit software
Rationale
C allows the use of either the array operator ([]) or pointers to access the elements of an array.
However, the use of pointers in C makes work difficult for optimizers in C compilers. Without
detailed and aggressive pointer analysis, the compiler has to assume that writes through a pointer can
write to any location in memory, including storage allocated to other variables. (For example, *p and
*q can refer to the same memory location, while x[0] and x[2] cannot.) Using pointers causes
aliasing, where the same block of memory is accessible in more than one way. Using array notation
makes the task of the optimizer easier by reducing possible aliasing.