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Techniques for global register allocation via graph coloring have been extensively studied and widely implemented in compiler frameworks. This paper examines a particular variant - the Callahan Koblenz allocator - and compares it to the Chaitin-Briggs graph coloring register allocator. Both algorithms were published in the 1990's, yet the academic literature does not contain an assessment of the Callahan-Koblenz allocator. This paper evaluates and contrasts the allocation decisions made by both algorithms. In particular, we focus on two key differences between the allocators: Spill code: The Callahan-Koblenz allocator attempts to minimize the effect of spill code by using program structure to guide allocation and spill code placement. We evaluate the impact of this strategy on allocated code. Copy elimination: Effective register-to-register copy removal is important for producing good code. The allocators use different techniques to eliminate these copies. We compare the mechanisms and provide insights into the relative performance of the contrasting techniques. The Callahan-Koblenz allocator may potentially insert extra branches as part of the allocation process. We also measure the performance overhead due to these branches. [ABSTRACT FROM AUTHOR]

Instruction scheduling is a necessary step in compiling for many modern microprocessors. Traditionally, global instruction scheduling techniques have outperformed local techniques. However many of the global scheduling techniques described in the literature have a side effect of increasing the size of compiled code. In an embedded system, the size of compiled code is often a critical issue. In such circumstances, the scheduler should use techniques that avoid increasing the size of the generated code. This paper explores two global scheduling techniques, extended basic block scheduling and dominator path scheduling, that do not increase the size of the object code, and, in some cases, decrease it. [ABSTRACT FROM AUTHOR]