Seminar | December 9 | 9-10 a.m. |  Zoom

 Alex Reinking

 Electrical Engineering and Computer Sciences (EECS)

This thesis details an emerging class of programming language designs, called
user-schedulable languages, that provide a safe and productive
performance engineering environment for modern, heterogeneous hardware. The
defining trait of user-schedulable languages is the division of program
specification into two key parts: the algorithm, which defines
functionally what is to be computed, and the schedule, which
defines how the computation should be carried out. Importantly,
algorithms have semantics independent of any schedule, and schedules are
semantics-preserving with respect to the algorithm. Thus, programmers are freed
from a large class of bugs. Because algorithm languages tend to be functional
and domain-specific, the scheduling language can be very expressive. Existing
scheduling languages include many program transformations, from accelerator
offloading to tricky tiling and interleaving strategies. Multiple schedules can
be written for different sets of hardware targets and can be maintained
independently from one another.

Here, we formally analyze the design of an existing and widely deployed
user-schedulable language, Halide, and find and correct several serious bugs
and design flaws through this analysis. We also detail both the design and
implementation of a new user-schedulable language, Exo, whose design is informed
by the lessons learned analyzing Halide. Unlike Halide, which models scheduling
as a parameter to a monolithic lowering process, Exo uses a rewrite-based
scheduling system. This system doubles as an instruction selection process
for custom accelerator hardware; importantly, these instructions can be
specified in user programs, rather than inside the compiler itself. We then
discuss a novel, high-performance, reference-counting memory management strategy
suitable for recursive programs with highly non-local control flow over a
(co-)inductive data domain. Finally, practical considerations for language
design are discussed; these are lessons learned from maintaining and deploying
these systems in practice.

 Jean Nguyen,,  510-642-9413

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Alex Reinking
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