Preventing Pointer Aliasing in C (for Scientific Computing Optimization Purposes)

The issue of pointer aliasing in C for those working with Scientific Computing code is probably a familiar issue. Pointer aliasing happens when more than one pointer refers to the same or overlapping memory region. This hurts performance in Scientific Computing code written in C. Pointer aliasing is probably the biggest issue which hurts performance of Scientific Computing code written in C compared to those written in Fortran. However, as of C99 standard, pointer aliasing can be "disabled" via the __restrict__ keyword. Most mainline C/C++ compilers supports this keyword. These are the relevant links for various mainline compilers/toolchains:

• Microsoft Visual C++ 2013: http://msdn.microsoft.com/en-us/library/5ft82fed.aspx
• GNU GCC: http://gcc.gnu.org/onlinedocs/gcc/Restricted-Pointers.html
• IBM XL C/C++ 7 for AIX: http://publib.boulder.ibm.com/infocenter/comphelp/v7v91/index.jsp?topic=%2Fcom.ibm.vacpp7a.doc%2Flanguage%2Fref%2Fclrc03restrict_type_qualifier.htm

This topic is also covered by Wikipedia at http://en.wikipedia.org/wiki/Restrict and http://en.wikipedia.org/wiki/Pointer_aliasing.

The most comprehensive explanation on this topic (with samples) that I found so far is at Understanding Strict Aliasing (by Mike Acton)

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