Re: Elaboration order

[l117593@cliffy.lfwc.lockheed.com (Cordes MJ)]

Robert Dewar (dewar@cs.nyu.edu) wrote:
: Mike says

: "As an aside to the RM discussion of this thread, how do I know
: that Ada compiler X will generate the correct (as defined in
: the RM) elaboration order?

: I know that ACVC tests do not guarantee correct code generation.
: Is the ACVC suite more complete when it comes to elaboration? Is
: there a standard benchmark used by compiler vendors? Or, for safety
: critical functions, should I verify this for every application
: build?"

: Of course the ACVC suite does not guarantee that a compiler gets the
: order of elaboration correct in every case. Your question seems to
: imply that you expected the ACVC suite to guarantee correct code
: generatoin and that the reason that it does not is that it is not
: complete. This is a serious misconception. No test suite can ever
: guarantee that a compiler has no errors -- indeed, except for very
: trivial programs, no set of tests ever guarantees accuracy.


You are reading things into the question which were not there. I was simply 
asking if it was generally held that elaboration order algorithms are
safer or better tested than code generation algorithms.

: For safety critical applications, you cannot trust ANY aspect of a compiler
: or any other tool that you use, and you need to carefully verify EVERYTHING
: about your program -- at least, put it this way, if you write the code for
: a plane that I will fly on, I will expect this!

Not exactly - industry cannot afford to verify *all* aspects of a program.
Risks are identified and analyzed and base on the analysis, something may
be done (e.g., redundancy, backup systems, additional testing). This is
true for all systems which go on a plane - not just SW.

A good software specific example is branch level testing vs path testing.
We do not perform full path testing of our applications because it (path
testing) is not cost effective. We perform other cost effective testing
on the application to reduce any and all risks to reasonable levels.

: Are there ACVC tests to test order of elaboration? Sure!
: Do they help ensure that compilers are correct in this respect? Sure!
: Do they guarantee that compilers are correct in this respect? NO!

THANKS!
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Michael J Cordes
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