[Pl-seminar] Reminder: Seminar TOMORROW: Thomas Wahl, Behavioral Non-Portability in Decision-Making Programs

[Gabriel Scherer]

The notes I took during the seminar are attached with, as always, the
questions people asked during and after the talk. Thanks for the
interesting talk! I'm curious to see whether a tool will emerge from
the work that would be usable by numeric program authors.

 On Thu, Sep 29, 2016 at 4:55 PM, Daniel Patterson <dbp at ccs.neu.edu> wrote:
>
> NUPRL Seminar presents
>
> Thomas Wahl
> Northeastern University
>
> 12:00pm-1:30pm
> Thursday, Oct. 13 2016
> Room 366 WVH (http://www.ccs.neu.edu/home/wand/directions.html)
>
>
> Behavioral Non-Portability in Decision-Making Programs
>
> Abstract:
>
> The precise semantics of floating-point arithmetic programs depends on the
> execution platform, including the compiler and the target hardware. Such
> platform dependencies infringe on the highly desirable goal of software
> portability (which is in fact promised by heterogeneous computing frameworks
> like OpenCL): the same program run on the same inputs on different platforms
> can produce different results. In other words, portability does not
> guarantee reproducibility, and this is a more or less accepted state of
> affairs.
>
> Serious doubts on the portability of numeric applications arise when
> differences in results are behavioral, i.e. when they lead to changes in the
> control flow of a program. In this talk I will first present an algorithm
> that takes a numeric procedure and determines whether a given input can lead
> to different decisions depending merely on how the arithmetic in the
> procedure is compiled and executed. I will then show how this algorithm can
> be used in static and dynamic analyses of programs, to estimate their
> numeric stability. I will illustrate the results on examples characteristic
> of numeric computing where control flow divergence actually occurs across
> different execution platforms.
>
> Joint with Yijia Gu, Mahsa Bayati, and Miriam Leeser, Northeastern
> University, Boston, USA
>
>
> Bio:
> Thomas Wahl joined the faculty of Northeastern University in 2011. His
> research concerns the reliability (whatever that means) of complex computing
> systems. Two domains notorious for their fragility are concurrency and
> numerical computing. With colleagues, Wahl has investigated how
> floating-point arithmetic can "hijack" a program's computation when run on
> non-standard architectures, such as heterogeneous and custom-made embedded
> platforms. You will witness some hijacking attempts in the talk today.
>
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