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Local and Global Optimization

Local optimization is that which can be done correctly based on analysis of a small part of the program.

Global optimization requires information about the whole program to be done correctly.


   I * 8           ==>       R1 = I * 8

   ...                       ...

   I * 8           ==>       R1
This is correct only if I is not redefined between the two points. Doing optimization correctly requires program analysis: a special-purpose proof that program P' produces the same output values as P.