Re: Fixing Bugs (Was: A Suggestion for Release Testing)

[Robert Dewar <dewar at adacore dot com>]

Scott Robert Ladd wrote:

> The ISO Standard doesn't prevent GCC from being *better* than specified,
> does it? Are we somehow breaking ISO compliance by doing math right? Is
> it so wrong to try and fix a problem that frustrates many people and
> makes GCC look bad?

No, but you are degrading performance unnecessarily by doing math to
conform to the Scott-Ladd standard, and we are not implementing SL C
we are implementing ISO C :-)

Of course it is perfectly reasonable to have well chosen options to
do more or less than the standard requires.
> With the attitude shown by Giovanni, there's really no point in
> submitting a patch, is there? Dozens of people have reported this
> problem, potential solutions exist, but any patch is going to be ignored
> because the bug isn't considered a bug by the Powers That Be.

It would be quite wrong to patch this unconditionally. The proper
patch would be one that provided a switch and a well defined semantics
for the switch, but this needs very careful design, and careful
review by people who understand fpt well.
> If I were to present a patch that implements the recomendations of the
> Numerical C Extensions Group, would it be accepted or rejected (on the
> subject alone; ignore for the moment potential technical bugs in the
> submitted code)?

Again, it would probably be better submitted under a switch. For
example on a machine like the Alpha, the impact of following these
recomendations is severe degradation of performance.
> Documentation for the compiler itself is woefully inadequate for someone
> "new". GCC may be old-hat to folks who've worked on it for years, but it
> is very complex and foreign territory for most non-compiler experts.
> Working on GCC requires a much broader knowledge than working on other
> projects, and without some sort of tutorial or guidance, working on it
> quickly becomes frustrating.

Compilers are complex beasts, I don't think you would expect to be able
to wade in and fix nuclear reactors without being somewhat of a nuclear
reactor expert. You can't expect to wade in and fix compilers without
being reasonably compiler literate. For those who are compiler literate,
GCC is certainly accessible. Sure, it could be made more accessible,
principally by adding more documentation. Patches to add correct useful
additional documentation are definitely welcome.
> Here's an example: Building new targets and fixing some code generation
> bugs involve changing the machine definitions, which are written in a
> rather uncommon language. Frankly, I haven't figured out all the nuances
> yet, mostly because I don't have the luxury of studying it, and I can't
> find any clear and comprehensive documentation.

These definitions are actually very clear, certainly they could not
be written in some normal programming language since they are essentially
denotational semantic definitions, for which a language like C would be
perfectly horrible. You need to invest the effort to fully understand
the machine definition language before you can do anything in this
area, and it is hard to see how it could be otherwise.
> Gentoo provides a mentoring system for developers. This is far better
> than GCC's "fix it yourself and send us the code" policy. There is no
> gentle way to become involved in GCC; it's a sink-or-swim, trial by fire
> environment. If I could get a half-dozen quick questions answered, and I
> could submit a couple of patches that are lying about on my hard drive.

There is no gentle way to become involved in any compiler, they are complex
beasts, and require a considerable investment of effort.

> I have submitted patches; I have tried to help with various aspects of
> GCC. I make no claim to having accomplished anything great, but I have
> tried, and watched patches die of bit rot while being told that certain
> bugs shouldn't be fixed.

I know of no bug (i.e. behavior non-conformant with ISO C) that someone
has said should not be fixed.
> Everything in life is a matter of give and take. People report bugs; you
> want someone to fix the bugs -- perhaps GCC should be more welcoming and
> helpful.

ANything to make it more welcoming and helpful is of course desirable, but
I think you are expecting too much if you expect an artifact of this
inherent complexity to be easily accessible, especially to people without
reasonably comprehensive training (i.e. at least a familiarity with compilers
at the dragon book level, and reading some of the crucial papers in the area).