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Colloquium - Bodik

Path-Sensitive Value-Flow Optimizations
University of Pittsburgh
3/8/1999
1:00pm-2:00pm

Current compiler optimizations are conservative and inflexible. As a result, even "highly optimized" programs execute half of their instructions redundantly, only to recompute previously computed values. Ideally, these values should be remembered and later *reused*, avoiding recomputations.

Unfortunately, this reuse strategy fails often. The main culprit is intermittent reuse -- one that exists only along some execution paths leading to the redundant instruction. This path-specific reuse is very common. How can we exploit it without paying the exponential price of optimizing each path separately?

This talk will describe a path-sensitive optimization framework that is powerful enough to achieve a near-complete redundancy removal, yet practical enough to permit an industrial-strength implementation. While the path-specific power is obtained by fusing three methods with complementary strengths, practicality stems from adaptability: when fusing the three methods, the optimizer biases itself towards the most suitable one, balancing cost and benefit.

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