Re: Testcases that assume argc != 0

[Mark Mitchell <mark at codesourcery dot com>]

Richard Sandiford wrote:

> Two testcases added this year assume that argc != 0.  Unfortunately,
> the standard specifically allows it to be zero, and MIPS libgloss
> takes advantage of this.
>
> As always there are too many options ;)  We could:
>
>   (1) Skip the tests on targets where argc might be zero.
>
>   (2) Change libgloss.
>
>   (3) Pass a nonzero value in some other way that is too complicated
>       for the optimisers to propagate as a constant.
>
>   (4) Make the test pass if argc == 0.
>
> (1) means building up a list of targets, which seems a lot of effort for
> such a small thing.

Agreed.

> I don't like (2) because I think what libgloss is
> doing is sensible when no executable name or command line arguments are
> available.  (The simulator could make them available through semihosting,
> but they aren't necessarily available on real boards.) 

Agreed.

(3) might perturb the original test too much.   I suppose the same is 
true of any change
> to the test itself, including (4), but I thought (4) was safer and was
> probably the way to go.

I think (3) would be better, especially given that there are only two 
test cases to change.  The reason I think it would be better is that 
then the testcases will continue to test what they are intended to test 
on targets without a command-line.  (4) is essentially like (1), from a 
validation perspective, although it is better from an engineering 
perspective, since it automatically skips the test on all platforms that 
are affected.

As I understand it, the goal here is to get the value "1", in such a way 
as the optimizers do not understand it to be a constant.  So, how about 
just:

  volatile int one = 1;

?  This should be forever immune from optimization and seems a 
relatively simple change.  If that works, and if yu like that approach, 
it's pre-approved.

However, as I write this, I don't have the GCC sources at hand, so it 
might be that I'm speaking nonsense.  If so, just say so. :-)

Thanks,

--
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713