Linear scan register allocation on SSA form

13 years 11 months ago

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The linear scan algorithm for register allocation provides a good register assignment with a low compilation overhead and is thus frequently used for just-in-time compilers. Although most of these compilers use static single assignment (SSA) form, the algorithm has not yet been applied on SSA form, i.e., SSA form is usually deconstructed before register allocation. However, the structural properties of SSA form can be used to simplify the algorithm. With only one deﬁnition per variable, lifetime intervals (the main data structure) can be constructed without data ﬂow analysis. During allocation, some tests of interval intersection can be skipped because SSA form guarantees non-intersection. Finally, deconstruction of SSA form after register allocation can be integrated into the resolution phase of the register allocator without much additional code. We modiﬁed the linear scan register allocator of the Java HotSpotTM client compiler so that it operates on SSA form. The evaluation ...

Christian Wimmer, Michael Franz

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