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From: jclark@src.honeywell.com (Jeff Clark)
Newsgroups: comp.compilers
Subject: Re: Debugging optimized code
Keywords: debug, report, optimize
Message-ID: <1990Jul31.182620.4651@esegue.segue.boston.ma.us>
Date: 31 Jul 90 18:26:20 GMT
References: <1990Jul30.180211.26558@esegue.segue.boston.ma.us> <1990Jul30.225825.28729@esegue.segue.boston.ma.us>
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Reply-To: jclark@src.honeywell.com (Jeff Clark)
Organization: Compilers Central
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In-Reply-To: pattis@cs.washington.edu's message of 30 Jul 90 22:58:25 GMT
Posted-Date: 31 Jul 90 15:09:59 GMT

In article <1990Jul30.225825.28729@esegue.segue.boston.ma.us> pattis@cs.washington.edu (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.

@TechReport{zell84,
  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
		 compilers.

		 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: jclark@src.honeywell.com		tel: 612-782-7347
uucp: jclark@srcsip.UUCP		fax: 612-782-7438
[A similar message from johnson@cs.uiuc.edu pointed out that the PARC
report is preferable to other sources because it contains graphics
missing from other versions. -John]
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