Global value numbering is a method of compiler optimization and is one of the applications of SSA (compilers). Basically, it sometimes helps reduce redundancy where Common subexpression evaluation (CSE) fails. Also, many times CSE may work better than this technique.
The reason that global value numbering is sometimes more powerful than common subexpression evaluation is because CSE matches lexical patterns of expressions whereas the former looks for "value equivalence".
For example, in CSE the code
a = c*d
e = c
f = e *d
will not be optimized!
Here global value numbering by assigning a number to each value helps.
For example a = c*d, is "value of a" <- "value of c" * "value of d" and in the expression f = e*d , the value of e happens to be value of that of value of c.
SSA form of the program makes it easier to track these values/definitions. So it is used to implement these numberings.
Globalvaluenumbering (GVN) is a compiler optimization based on the SSA intermediate representation.
Globalvaluenumbering is distinct from local valuenumbering in that the value-number mappings hold across basic block boundaries as well, and different algorithms are used to compute the mappings.
Globalvaluenumbering works by assigning a valuenumber to variables and expressions.
One may be forgiven for thinking that globalization would bring about the end of narrow nationalism, selfish isolationism and the reckless pursuit of commercial and economic interests.
The globalization of the knowledge industry appears to be a boon for all.
Globalization of the culture of the rich, marked by extravaganza and lack of social commitments, is deeply troubling for the future of the poor.
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