Editing XOR swap algorithm (section)

==Reasons for avoidance in practice==
On modern [[CPU architecture]]s, the XOR technique can be slower than using a temporary variable to do swapping. At least on recent x86 CPUs, both by AMD and Intel, moving between registers regularly incurs zero latency. (This is called MOV-elimination.) Even if there is not any architectural register available to use, the <code>XCHG</code> instruction will be at least as fast as the three XORs taken together. Another reason is that modern CPUs strive to execute instructions in parallel via [[instruction pipeline]]s. In the XOR technique, the inputs to each operation depend on the results of the previous operation, so they must be executed in strictly sequential order, negating any benefits of [[instruction-level parallelism]].<ref>{{cite web |first1=Saman |last1=Amarasinghe |first2=Charles |last2=Leiserson |title=6.172 Performance Engineering of Software Systems, Lecture 2 |year=2010 |publisher=Massachusetts Institute of Technology |website=MIT OpenCourseWare |url=http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-172-performance-engineering-of-software-systems-fall-2010/video-lectures/lecture-2-bit-hacks/ |archive-url=https://web.archive.org/web/20150125102630/http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-172-performance-engineering-of-software-systems-fall-2010/video-lectures/lecture-2-bit-hacks/|url-status=dead|archive-date=2015-01-25 |access-date=27 January 2015}}</ref>

===Aliasing===
The XOR swap is also complicated in practice by [[aliasing (computing)|aliasing]]. If an attempt is made to XOR-swap the contents of some location with itself, the result is that the location is zeroed out and its value lost. Therefore, XOR swapping must not be used blindly in a high-level language if aliasing is possible. This issue does not apply if the technique is used in assembly to swap the contents of two registers.

Similar problems occur with [[call by name]], as in [[Jensen's Device]], where swapping <code>i</code> and <code>A[i]</code> via a temporary variable yields incorrect results due to the arguments being related: swapping via <code>temp = i; i = A[i]; A[i] = temp</code> changes the value for <code>i</code> in the second statement, which then results in the incorrect <code>i</code> value for <code>A[i]</code> in the third statement.