Re: [avr-gcc-list] Wrong excution order in 4.1.1, but not 3.4.5, regression?

[David Brown]

Bob Paddock wrote:
> On Monday 19 February 2007 19:34, Eric Weddington wrote:
>
> > I can't fully tell what's going on with just the asm snippets you provide.
>
> I spent a while trying to get a reproducible version in a few
> lines, but that kept changing the results.

If you can't post a cut-down version, then at least post a compilable 
section of your code with the minimal necessary typedef's and other 
definitions included.  To be able to test your code, people will have to 
be able to reproduce the bug.

If the same code is generating assembly with different ordering despite 
the volatiles, then it is quite likely that there is a bug somewhere. 
However, I don't know if the C standard is clear on expressions such as 
"a = b = c", when some or all of these are volatile - it could be that 
both implementations are correct because the rules are not strict.  At 
the risk of sounding patronising, I'd say that almost any code with "a = 
b = c" expressions is incorrect code because it is far from clear what 
you mean, and if volatiles are involved then it is undoubtedly wrong. 
When the code is re-written to actually say what you mean, do you still 
get a difference?

Regards,

David


> > If you think that this is a GCC bug, then please fill out a GCC bug report.
>
> All I know for sure is the code compiled with 3.4.5 works, with 4.1.1
> it does not.
>
> > Thanks for checking the known bug list first. :-)
>
> > If you fill in a GCC bug report, feel free to put my email address on the CC
> > list of the bug report.
>
> Ok.  I'll try to take care of that in the morning.  For now I'll just keep
> using 3.4.5, the code produced there looked far less convoluted, plus
> the added bonus of working correctly. :-)