Optimization techniques are implemented by means of a program analyzer (16) used in connection with a program compiler (12) to optimize usage of limited register resources in a computer processor. The first optimization technique, called interprocedural global variable promotion allows the global variables (g1,g2,g3) of a program to be accessed in common registers (110,113) across a plurality of procedures. Moreover, a single common register can be used for different global variables in distinct regions of a program call graph (130). This is realized by identifying subgraphs of the program call graph (130) called webs (150,152,154) where the variable is used. The second optimization technique, called spill code motion, involves the identification of regions of the call graph (130) called clusters (158,160,162) that facilitate the movement of spill instructions to procedures which are executed relatively less often. This decreases the overhead of register saves and restores which must be executed for procedure calls.
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