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[OT] Deugging optimized code (was: [22.1.90]: Point before start of prop

From: Stephen J. Turnbull
Subject: [OT] Deugging optimized code (was: [22.1.90]: Point before start of properties)
Date: Sat, 23 Feb 2008 07:20:32 +0900

Stefan Monnier writes:
 > >> Debugging optimized code is [...] a wrong question.
 > > Intel thanks you for your marketing of their future products!
 > I guess I do, but I don't think you quite understood what I meant:

Oh, I know more about what you do than you seem to think. ;-)  A
little bit, but that's enough.

 > That's what I meant by "a wrong question": instead of solving the
 > impossible debugging problem after-the-fact (after the optimizer
 > has done its thing), you can solve a different problem (annotate
 > the source program) instead.

First of all, this requires a reproducible problem.  That has two
issues: (1) maybe the problem isn't reproducible, and (2) for me at
least reproduction is a waste 90% of the time; the bugs I'm capable of
solving are typically apparent in the stack trace. :-)

Second, you're basically restricting the transformations that are
allowed to the translator.  This seems a reasonable strategy to me,
but it's not going to help with Type 2, 3, or 4 bugs, and it may
interfere with Type 1 bugs (eg, if you need to execute a loop a few
billion times to reach the buggy state -- proof of concept strawman).
More Intel The Next Generation promotion. :-)

So I wouldn't go so far as to say the question is "wrong", just that
there are better questions for a lot of debugging problems.

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