I was gathering some information of GCC with respect to my prior article. And I found that GCC is converting code into SSA form: http://gcc.gnu.org/wiki/SSA. SSA stands for "Single Static Assignment."
It is quite surprising me, because DEF-USE relationship is used for software testing and I haven't thought testing and compiler is related; indeed they must be able to share big amount of parsing technique.
In addition, personally I prefer to use "const" keyword for every single local variables. Some programmer don't like to see const keywords, because it makes source code longer. And they may think it increases the number of local variables and therefore it increases the size of the binary code. If compiler is internally converting to SSA form, then there is no way to reduce the binary code size by not using "const".
Hence I found a better excuse to keep using const keyword for local variables. :-)