Re: Debugging optimized code (Jeff Clark)
Tue, 31 Jul 90 18:26:20 GMT

          From comp.compilers

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Newsgroups: comp.compilers
From: (Jeff Clark)
In-Reply-To:'s message of 30 Jul 90 22:58:25 GMT
Posted-Date: 31 Jul 90 15:09:59 GMT
Keywords: debug, report, optimize
Organization: Compilers Central
References: <> <>
Date: Tue, 31 Jul 90 18:26:20 GMT

In article <> (Richard Pattis) writes:

> Polle Zelweger. Her thesis was done with John Hennessy at Stanford, but
> Polle got her Ph.D. at Berkeley (both institutions may have published the
> Thesis). She is now at Xerox PARC.

It is available as Tech. Rpt. CSL-84-5 from Xerox PARC. The citation and
abstract follows.

    author = "Polle T. Zellweger",
    title = "Interactive Source-Level Debugging of Optimized Programs",
    institution = "Xerox Palo Alto Research Center",
    year = "1984",
    OPTtype = "Research Report (PhD Thesis)",
    OPTnumber = "CSL-84-5",
    OPTaddress = "3333 Coyote Hill Road, Palo Alto, California 94304",
    OPTmonth = "May",
    OPTabstract = "The transformations performed by an optimizing compiler have
traditionally impeded interactive debugging in source
language terms: after optimization, a program's source text
and object code do not have a straightforward correspondence.
This dissertation shows that effective interactive
source-level debuggers can be provided for optimized
programs. Such debuggers can reduce debugging time and
programmer confusion. These benefits are especially
important given the increasing availability of optimizing

The first half of the dissertation studies the overall
problem of debugging optimized programs. It presents a
general view of debuggers and defines two important levels of
debugger behavior for optimized programs. A debugger
provides ``expected behavior'' if it hides the effects of the
optimizations from the user by doing behind the scenes
processing. It provides ``truthful behavior'' if it
indicates that it cannot give the exact answer to a debugging
query (because the executing programs differs from the source
program). The user may be able to deduce the correct answer
from the partial information displayed by a truthful
response. A thorough study of the interactions between
optimization and debugging is included. In addition, a
collection of solution techniques to relieve the problems
caused by optimization are described.

The second half of the dissertation describes implementation
experience with one aspect of the problem. A prototype
debugging system called Navigator was developed for the Cedar
programming environment at the Xerox Palo Alto Research
Center. Navigator can be used interactively to monitor
program execution flow in the presence of two simple but
nontrivial optimizations: inline procedure expansion and
cross-jumping (merging identical tails of code paths that
join). Navigator provides expected behavior by combining
information collected by the compiler about the effects of
the optimizations and information collected by the debugger
about the control-flow history of the computation. Program
execution space and speed are almost totally unaffected when
no debugging requests are active. When debugging is
requested, Navigator provides its added functionality without
noticeably degrading debugger response time for most
programs. Proofs of correctness of the compiler and the
debugger algorithms are given, as well as an analysis of
their efficiency."}

Jeff Clark Honeywell Systems and Research Center Minneapolis, MN
inet: tel: 612-782-7347
uucp: jclark@srcsip.UUCP fax: 612-782-7438
[A similar message from pointed out that the PARC
report is preferable to other sources because it contains graphics
missing from other versions. -John]

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